Thanks to Gordon Killebrew for the chart.

QUESTION: My ZR-1 runs hot, anything I can do to improve this?

ANS: For some applications it is known that the stock ZR-1 cooling system has proven to be inadequate. This has been born out through observations by many individuals on the ZR-1 Network. Various options have been explored with one option, two suppliers, proving the be the most viable fix to over heating.

The larger radiator from Doug Rippie Motorsports and the unit from Lingenfelter Performance Engineering both have proven themselves to be very well made pieces of equipment. They do an excellent job at keeping engine temperatures in a very comfortable zone under the most extreme conditions of operation. Typical operating temperatures run in the 90c-97c range, the upper end under track conditions. This is well below the 112c temperatures witnessed by several people.

With many members of the ZR-1 Net having installed one of these units, not one disparaging remark has been made, only glowing reports. We all highly recommend one of these units in addition to a Doug Rippie modified thermostat. In bang for your buck, this is one of the best values you can possibly do.

Thanks to Jim Milstead for this information.

More important for proper cooling, is a clean and unobstructed radiator, and possibly a modified prom calibration. Take a half day and remove the top shroud of your radiator from the top. Look down in between the AC condenser and the radiator and you'll be shocked. If car show judges could find a bent up mirror to get down in there, all you waxers would be in misery! It's filthy! As Corvettes are bottom feeders, we've found that the radiator's airflow is severely obstructed in many cars. This is not visible from the bottom but sometimes you can see a little through the oil cooler line cut outs in the passenger side of the shroud.  We've also made a pipe that screws onto a hose that is about 3 feet long. At the end, we put a 90 deg. elbow. After the shroud is removed, this pipe can be used to "reverse" flush the radiator fins with water. This will help. Just for info: We've also found that most ZR1's out here in furnace land will gradually start overheating after 3 to 4 years no matter what. With the addition of a new radiator, they run cooler than ever. Adding a Stant t-stat and recalibrated prom helps even more.

Also the stock cooling fans were manufactured with several air holes in the case. Wet climates or washing the shroud area will allow water to settle within the electric motor. Along with dirt and dust, this causes the motors to get weak over time. The new motors, part number 15-8484, do not have any breather holes and are a sealed unit which eliminates this problem. In addition, I believe they turn more RPM's.

You'll also want the new blades 15-8468 which flow much more air than stock.

Thanks to Jim VanDorn for this info.

More on cooling........

There is a coolant bypass device in the stock ZR1 cooling system which does compromise the cooling ability of the package, the same is true of the oil cooling system. My recommendation is to install an aftermarket radiator with sufficient flow capacity to cope with the 100 USGPM that the water pump is capable of. But I would strongly advise against altering the pressure setting of the radiator since the system is very sensitive to pressure variation. The typical failure mode with either too little or too much pressure is material erosion in the pump itself (caused by cavitations) and also in the cylinder liner and seat areas caused by nucleate boiling. Which is basically small pockets of super heated coolant near the metal surface flashing to steam and eating away at the part in question. During its development phases the LT5 was run at several dyno facilities other than Lotus, each time we had to ensure the correct parameters for the cooling system or holes would appear in the early running life of the engine. So if you wish to change the system pressures be warned, puddles of coolant may be prone to appearing on the floor and/or the oil level in the pan may rise.

In so far as the oil cooler is concerned, the stock unit is not capable of dealing with the heat rejected to the engine oil at sustained high speed operation, no matter when the waxstat opens. So fit a cooler that is and then it doesn't matter where the stat opens since the cooler is capable of coping with the heat rejected by the engine. If people insist on earlier opening of the oil cooler lines then simply buy and fit a lower temp waxstat, since the unit is pretty similar to many water thermostat devices, this should not be too hard to find. Furthermore there is a constant controlled leak across the valve to ensure that cooler opening in extreme cold conditions does not result in oil pressure loss due to the cold slug of oil being pushed into the engine.

P.S. the amount of power to coolant flow rate was 4bhp to 1 gpm as a rough rule of thumb.

Thanks to Graham Behan of Lingenfelter for the above info.

QUESTION: I need to touch up my '94/'95 wheels, what color paint do I use?

ANS: Go to your local hobby store the one that sells plastic models, and get a paint that is made by Tamiya. Its called Tamiya color, Acrylic Paint and the code number is X-11 (chrome silver). Don't worry about the color (chrome sliver) when it dries its the exact same color as the wheel. Just remember to stir the paint and do not shake it.

Touch up the ding with a small soft brush filling the ding to just higher than the surface of the surrounding paint. Let dry for 24hrs then lightly buff down with some polishing compound to the same surface level of the rest of the paint. Be sure that the wheel is cool before attempting to touch it up.

Thanks to Pete Bordonali for this info.

Another member has found Testors #1181 Aluminum FLAT ENAMEL in the little tiny bottle (like kids and dads use for model airplane building). It is very close and looks great. And it's cheap - $1.10 at Michaels craft stores. It makes the outside wheel weights almost disappear too.

Thanks to Randy Schulkers for this info.

QUESTION: I'm having problems with my INFL REST light coming on.

ANS: Well, it seems as if all us 90 owners have experienced the famous "INFL REST" problem. I have also had the problem, and in my case I was able to fix it for free. Mine was a code "25" which is a "Front Sensor #2 (RH); Open Circuit". The most likely reason for this failure is corrosion under the sensor. The reason for the corrosion is AC accumulator run-off. The water drips down from the accumulator and runs down the frame rail to the sensor. It wicks under the sensor, and corrodes the bolts and holes. This opens the connection to ground, and creates the error #25 condition. Mine goes out each summer (when I'm using the AC) and I have to re-clean the connection. Here's the procedure to fix.

1. Read the stored codes. (They remain, even after a battery is disconnected)

1a. Turn ignition switch to "Off". 1b. Ground ALDL terminal "K" to ground ("A"). Consult the manual pg. 9J-A-3 for picture of ALDL connector. (Too hard to explain)

1b. Turn ignition switch "On".

1c. The flashes of the "INFL REST" indicator lamp correspond to the digits of the two digit malfunction codes. Code 12 will be displayed three (3) times, followed by any other codes, which may be stored. Each code will flash three (3) times. After all the codes are displayed, the sequence starts over with "12" again. If you have a code "25", you can proceed. Here is a total listing of all the codes;

14 Front Sensor #1 (LH); Short to Ground

15 Front Sensor #1 (LH); Open Circuit

16 Front Sensor #1 (LH); Sensor Fault

24 Front Sensor #1 (RH); Short to Ground

25 Front Sensor #1 (RH); Open Circuit

26 Front Sensor #1 (RH); Sensor Fault

31 Inflator Squib; Current leakage to Battery

32 Inflator Squib; Current shorted to battery voltage

33 Inflator Squib; Current leakage to ground

34 Inflator Squib; Current shorted to ground

35 Inflator Squib; Open circuit

36 Inflator Squib; Squib fault

41 Indicator lamp circuit; Shorted to battery or ground

42 Indicator lamp circuit; Open circuit

51 Diagnostic unit faulty

52 Firing sequence confirmation set

53 Firing current confirmation set

54 Squib current has flowed

2. Disconnect the battery. (You don't want the SIR to fire when your working) You should also wait 30 minutes after disconnecting battery before working any SIR problem.

3.Remove the passenger side front tire.

3a.Remove the rear inner wheel well. It has an assortment of Torx and hex head bolts.

3b. You will now be able to see the sensor, which is mounted on the frame rail. (It is located towards the back of the wheel well area. The box is around 2x3".

3c.The sensor has 2 different bolts securing it. (13mm and 10mm I think). Remove them (Yes, it's is very hard to get the rear one out).

3d. Carefully work the sensor forward out of its position. The cable has some slack, and will allow a few inches of movement. It is just enough to get the sensor up out of the way, to allow for cleaning.

3e. Once removed, you can clean up the surface and apply some dielectric grease to the surface to keep the water out. Make sure you clean both the frame and the sensor. Mine was very wet and greasy. The main grounding comes from the bolts, so make sure they cleaned up. If the bolts show a lot of corrosion, replace them.

3f. Carefully reassembly everything. The back bolt again will be a real bear.

4. Re-connect the battery.

5. You must now clear the codes. (You may want to try this first, as the water may have evaporated. Sometimes my codes will go away for months, after simply clearing the codes.

5a.Turn ignition switch to "Off".

5b.Ground ALDL terminal "K" to ground ("A"). Consult the manual pg. 9J-A-3 for picture of ALDL connector. (Too hard to explain)

5c.Turn ignition switch "On".

5d.The codes will flash as before.

5e. Wait for the fault codes to flash. (Approx. 5 seconds). When they do, unground ALDL terminal "K" for 3 seconds +/- 1/2 seconds. (The timing here is critical, and you may have to try a couple of times). After ungrounding; ground it again for 3 seconds +/- 1/2 seconds. Unground again and wait 10 seconds.

5f.Code 12 should now be the only fault. If not, redo section 5 again.

It has been a while since I have performed this procedure, so use at your own risk.

Thanks to Mike Zeeff for this information.

QUESTION: What happens if I remove all my Low Tire Pressure sensors?

ANS: For the 1990 and 1991 ZR-1's nothing. You will not see any error indications on your dash. It'll be as if you never had the LTPWS option.

For 1992-1995 ZR-1's your LTPWS error light on your dash may light. Telling you your system has malfunction. Whenever you remove all 4 wheel sensors you will get a code 99. It may not appear right at first and can go up to 200 miles before it turns the light on and sets the code, but it will happen. There are two things that can be done and both require removing the DIC.

One is to remove the 2 lights in the upper right hand corner of the DIC and the other is to unplug the module. This can be done by using a hook to fish the connector out to where you can unplug it.. The module is attach to the right side of the speedo cluster and can be seen through the hole behind the DIC. It has a pink wire and a black wire going to it, after 91 there is a third wire, tan.

The easiest thing to do is to remove the DIC and remove the 2 light bulbs or you can also remove the cruise control fuse, which will also disable illumination of the LTPWS lights; of course, that option disables the cruise control function.

Thanks to Jim VanDorn and Jerry Watts for this information.

QUESTION: Sometimes I have problem with my ZR-1 not starting.

ANS: Could be one of several problems.

 
1. The VATS system.
2. A starter problem.
3. The clutch safety switch.

For number one, VATS, a quick way for a technician to diagnose a VATS problem is to hook up a Tech 1 scanner. When the vehicle fails to start, display the VATS parameter and note what it says. If it says "VATS enabled" then you've tripped the VATS system and have eliminated other possibilities. This will reset itself after 5 minutes provided NO OTHER ATTEMPTS TO START, OPEN DOORS, ETC OCCUR. A common cause of the VATS problem is the ignition cylinder, which has been updated. If this occurs, change to a new (spare) key and try it. Also, if the VATS system is the problem, try unlocking the driver's door with the door key a couple of times. As most of you already know, the door key switch deactivates the UTD alarm and this switch is known to go out after time (it's obviously the most used).

Also note if the security light is on while trying to start the ZR-1. If it is then it's your VATS system. Also if you wait 15 minutes and then try to start it and it starts that also says it is your VATS system.

From Jerry Watts: If the ccm sees the wrong resistance or no resistance when the key is turned to the start position it will set a code 54. Any time there is a ccm code that is active your cluster will flash. If the vats system fails, it will not turn on the fuel pump when you first turn the key on, this you should be able to hear; also you could not push start the car because of no fuel and the injector will not be pulsed.

For number 2, the starter, the most probable problem is that your starter has gotten wet. Have you rinse down the engine lately? If it is the starter, then you should be able to park it on a hill and turn it off, try the starter and if it doesn't start, then jump start it by rolling a little. This eliminates the PASS Theft deterrent system and leaves either the clutch safety switch, or the starter itself.

From Jerry Watts: G.M. issued a bulletin back in October of 92. While working at the action center we received a lot of calls concerning this problem. If you wash your engine or are in a high humidity area the starter can corrode because of its location. Later the drain hole size was increased to help with this problem but, it was found this was not a 100% cure. The starter can be taken out and cleaned and put back if you wish.

For number 3, clutch safety switch, to check the clutch safety switch use an ohm meter to make sure the switch is opening and closing right or the real fix for this problem is to remove the switch, re-crimp the wire connectors going to it, then re-install the switch. In many cases this should fix your starting problem.

Thanks to Jim VanDorn for this information.

Note: From another member on checking clutch switches. There is an easy way to check the clutch safety switch, assuming the starter isn't starting. Set the parking brake, put the shifter in neutral, and watch the voltmeter while you turn the key to the start position. The voltage will drop slightly. While holding the key in start , release the clutch pedal. If the voltage goes up and down in response to clutch pedal movement, the clutch switch works.

QUESTION: The feeling of loss power under heavy acceleration.

ANS: There can be several reasons for the feeling of loss power. One is the collapse of the air duct. But another possible problem as written by one of our members.

Since we are on the "loss of power" subject I thought it might be helpful to share an experience that I had a couple of months ago. I also experienced "loss of power" under heavy acceleration - she (LT5) just won't hookup. In addition, I also heard a "moaning" kind of noise that really sounded like a vacuum leak. So my mechanic, spent a couple of weeks, off and on, chasing the vacuum problem. He ended up replacing all of the vacuum hoses, tubes and MAP sensor, even those under the plenum.

None of this helped and the problem persisted. We did notice something, though, that when he pulled the plenum and looked at the secondaries it looked like they had not been operational in a while. As a last resort we called Jerry Watts and Gordon Killebrew. Yes, they diagnosed the problem - damaged fuel pump. Many thanks to the guys.

Solution: (or my understanding of it) The computer had damaged one of the two fuel pumps and therefore the engine was starved for fuel under heavy acceleration. Hence the loud sucking "moaning" sound. So my mechanic replaced the computer and fuel pump. Guess what.......yep, no more problem. Now she runs like new.

Thanks to Lauren Groth for this information.

Also on hard high speed turns like on the track you may feel a lost of power which can happen if your fuel tank is less than half full.

QUESTION: How many 1990 ZR1s were shipped with manual AC (C60)?

ANS: A total of 124 1990 ZR1s were built with Manual AC (C60). After 1990 Electronic AC (C68) became the standard.

QUESTION: Can the surface of the flywheel for a ZR-1 be machined?

ANS: The flywheel cannot be machined on the LT5. Get another flywheel and also order the weight kit (which nobody knows about at the dealer) for balancing purposes. You will need to look at your present flywheel and note where the weights are placed in the holes at the outer edge. Insert the new weights in the matching holes of the new flywheel.

Thanks to Jim VanDorn for this info.

QUESTION: Why is the cost for the valve cover emblems so expensive?

ANS: Nobody knows, but the 1990 emblems are around $22.00 while all other years are around $125.00. The 90 emblems had a red background behind the bowtie (84-90 emblem) while 91-95 had a black background.

QUESTION: I understand there is a build sheet somewhere on the ZR-1?

ANS: Yes in maybe two places. One on the fuel tank and one in the left front suspension area of the ZR-1.

First the tank sheet and build sheet are the same. It's basically a computer generated birth certificate for your car. It has the date/time built (actually its the date the sheet was printed) all the RPO codes, their explanations, and shows all your codes for the suspension components, seat belts, air bags, colors, dealership, the whole works.

I've never found one on the interior of a late model, but getting the tank stickers off is not difficult.

Start by removing the spare tire and tray from underneath the back of the car.

Lay under the car and look between the gas tank and the vertical piece of fiberglass where the rear compartment is. You will see the tank sticker the tank, you can gently remove the paper from the adhesive. How much glue is there depends on how good a mood the guy at the plant was in that day. I've seen some with virtually NO glue, to some that were completely glued on. Sometimes, on some prototypes I've seen, the guys would get cute and write "ZR-1" in the glue. Usually, ZR-1 is written across the sticker in Red marker. Maybe you will get lucky and have had someone at the plant leave a personal note on the sticker. "Kick Ass" and "King of the Hill" are popular themes.

It is definitely worth going after.

If that sticker is missing for some reason, and you really want to know.....

This is supposed to be a secret, but I was never charged with guarding it, so here goes....There are additional copies of the build sheet in the left front suspension area of the car. I'm going to take a closer look at one of the '89s later, but I think if you remove the lower A-arm, and maybe the spring on the drivers side, you can retrieve it. The paper is inside the cross member where it is bolted to the frame. A really bright flashlight will allow you to find it by looking into the oval holes in the cross member from the top (near the motor). You will see the paper in the hole, then you can figure out how to get to it. The only one's I've ever retrieved were by dropping the cross member, but its probably possible to do it without so much disassembly.

Thanks to Ed Simmons for this information.

QUESTION: How good is the clear coat on my wheels?

ANS: After working for an OEM aluminum wheel supplier in the capacity of production engineer in charge of the paint process, I can possibly lend a bit of light to the clearcoat durability issue. This problem is not in any way specific to either GM or Corvette, it is an industry wide problem that is being addressed in different ways by the different manufacturers.

As a side note, the company that I worked for supplied wheels to GM, Toyota, Mazda, Ford, Nissan, Subaru, and a few other companies. Of all of the companies, GM took the most aggressive approach to solve wheel durability problems found over the last 7 years or so.

SOME PROBLEMS:

1. Wheels are in the worst possible environment for paint. They get banged up, cut by wheel weights, go through outrageous temperature fluctuations (32 degrees out, you slam on the breaks in a panic stop, wheels jump 100 degrees or so in a few seconds, paint stresses as a result), and get hot brake dust spewed at them constantly.

2. Aluminum can be a bitch to paint, especially when the paint is a clearcoat over the machined surface. As you may know, water beads up on aluminum (it is not a really wetable surface). Paint also wants to bead up on the surface - this would be bad. To coerce the paint into sticking to the aluminum, a conversion coating must be applied. The most durable clear conversion coating is chromium chromate (not to be confused with chrome plating). A basic paint process is as follows: A wheel is sent through a pretreatment system (industrial washer) where it is cleaned with an alkaline detergent, rinse, converted either by spray or immersion in an acidic bath composed of chromic acid, accelerators (fluozirconic acid, for one), and etching agents (hydrofluoric acid, for example), sent through a series of counter flow rinses (each rinse is fed from the following stage), and finally rinse with pure deionized water to eliminate spotting. After all of this, the wheel is clear coated with either a solvent acrylic clearcoat (i.e. Japanese suppliers) or powder - polyester or acrylic - clearcoat.

3. The durability adhesion (paint film resistance to peeling from a scribe line after being introduced to a corrosive environment) tends to improve with both higher levels of the chromium conversion coating. The problem with this scenario is that the conversion coating tends to turn green or gold as the coating weight (area density) of the coating increases. As such, the ideal conversion coating weight is not always easily attainable when the machined surface is to be clearcoated. On fully color painted wheels and in the painted windows of machined wheels, the suppliers can load up on the chrome since the basecoats will cover the coloration.

SOME SOLUTIONS (PARTIAL LIST):

1. To ensure a more robust conversion coating, many manufacturers are mandating a deoxidation stage in the washer prior to the chrome stage. This will ensure that the conversion coating is more uniform and therefore more durable. This results in a better substrate for the paint to adhere to at any given coating weights because the weak areas are eliminated.

2. Powder clearcoat technologies (the most widely used clearcoat process for wheels) are being switched from polyester to acrylic paints. The acrylics are more resistant to environmental problems, such as peeling and filiform corrosion (this looks like worm tracks under the painted surface).

3. Some OEM manufacturers are moving away from clear coating machined wheels and sticking to base/clear wheels (Such as on the later ZR-1s, Indys, Grand Sports, and Collectors) until the problems can be better addressed.

<< Does anyone have any suggestions on keeping the clearcoat like new. >>

Treat it just like on any other painted surface. I would recommend staying away from the "wheel cleaners", as some of the ingredients of some of these cleaners can cause corrosion problems. This information was supplied by a leading paint manufacturer who tested all of the popular cleaning solutions. I'm not sure which are good and which are bad, so I avoid them all. I simply slap a coat of Liquid Glass on the wheels and keep them clean with a moist rag.

Thanks to Dan Stauft for this information.

QUESTION: How do I know if the odometer hasn't been changed or the ZR isn't a savage?

ANS: Odometer tampering....Hmm...This is a tough one to catch on any C4 Corvette...Tougher on the '90 and ups, but all anyone has to do with one of those is swap a CCM out of another car with lower mileage...The only roadblock in the way of that would be the VATS system...However, if someone is going to go to the trouble to swap a CCM, he will likely have the capability to scan the CCM and get its VATS code...It is then a simple matter of cutting a new key (with the existing pattern) with the right resistance...You can look for loose dash screws, but that won't tell you much...

The only way to really catch a "clocker" is with the documentation of the car...Get copies of all the previous titles from the DMV.. Get the previous registration slips, look for oil change and maintenance receipts....Find out if it was dealer serviced, and if it was, they can run a complete computer history of all the maintenance, with the mileages....With this information, it should be pretty easy to catch something...Look for the obvious signs of high mileage, such as worn pedals, ripped seats, etc..

I will say, however, that there is potentially nothing wrong with a ZR-1 that has 200,000 miles on it....It all depends on how well they are taken care of...

Previous wrecks and salvage cars are another valid thing to check for...The title search will show a salvage history in most cases...It is possible to buy a car with a "clean" title that has been totaled in the past...I think its good that you can, because if you buy such a car, assuming you know it was salvaged, you don't want the hassles of your bank or insurance company not treating the car with its proper value...

 Many will argue that a prior salvage car shouldn't have as much value, but personally, I disagree...Many cars get totaled and branded with salvage titles that shouldn't be...It is so easy for a body shop to inflate the damage estimate of a car they don't want to fix, and have it totaled, its pathetic...Whenever there is a hurricane or other natural disaster, for example, many cars with just paint and glass damage get totaled, simply because the body shops can't handle the load, and the insurance companies don't want to spend thousands on a rental car while they wait for repairs to be made...

There are also many cars that should be legitimately totaled, but don't get reported to the insurance, and are then sold with good titles, no matter how bad the damage...Unfortunately, cars like this sometimes have the Identification numbers removed and transferred to a stolen car...This is HARD to catch, but only if done properly.....If you have any doubt, look for the hidden numbers on the frame rail, look at the engine and trans numbers...Look at the VIN plate closely....Check the RPO label, and if you have any doubt, check the build sheet...Documentation, Documentation, Documentation....Most car thieves won't bother to change everything.. Unfortunately, some dealers end up with cars like this unknowingly, and then pass them on to the consumer...

You should have nothing to fear from a PROPERLY repaired ZR-1 that has been damaged, but you can get some leverage in the price, usually...Here are some clues I've encountered that would indicate that a car has been wrecked or repainted...

Look on the inner front corners of the front bumper cover where the wiring for the headlights and parking lights run....Bad repair work always shows up in UGLY wiring...Look for splices, or misrouted harnesses...This is a dead giveaway...Also look at the hardware on the radiator support, hood hinges, etc.. another thing body shops always screw up...Look for cracks in the inner wheel surrounds...look at the shims on the upper control arms...You will notice too many, or too few if bad framework was done....Check the tire wear...Look at the floors for obvious dents or fiberglass repairs...Look for over spray into the engine compartment...Look for paint on the front spoilers...Also look where the gaps in the headlight pods would let paint through to the area underneath...Take out the rear license plate and an inner taillight in the back bumper...If the gas tank, or a taillight socket is the same color as the body, its been repainted...Look under the hatch weatherstrip for paint, check the Federal label on the door, make sure it matches the VIN...If its missing, you may have had the door changed. Look inside the rear compartments for shattered hatch glass...You can never get it all out...Look at the door jambs....Ugly repair work always shows up where the quarters are bonded....Look under the car for anything obvious...Note, some cars had the paint touched up at the plant, so don't automatically assume that over spray means the car was wrecked...

If you don't see any of that, more than likely the car was :

A) never hurt, or

B) repaired properly....Again, talk to the previous owners, and get DOCUMENTATION....

Take a friend along, two sets of eyes are always better than one...

That's a few of my ideas, I'm sure there are more....

Thanks to Ed Simmons for this information.

QUESTION: What if I need a brake job, what should I look out for?

ANS: I ran across some interesting research GM-STG has done on brake servicing, specifically brake rotors and customer complaints of brake pulsation or "shudder" above and beyond ABS brake pedal feedback. Brake work is a huge business adding up to about 40% of all auto service work in the U.S. Complaints of "warped rotors", "shudder" and pedal pulsation are generating many of the repair orders. Recent industry investigating shows that much of the work being done to eliminate shuddering is actually making the problem worse causing customer dissatisfaction.

Question why shops fail to adequately repair disc brakes?

-Service techs need the skills of a trained, experienced machinist to machine disc rotors properly and many simply do not have this level of training.

-The fine finish on today's lightweight brake rotors is almost impossible to duplicate on many shop brake lathes, no matter how skilled the operator

-Too many lathes in too many shops are poorly maintained. If the arbors are nicked and worn, the mandrels damaged or dirty or the tool holders are not in perfect condition, future trouble with any rotors that are machine on that piece of equipment is a certainty.

When does rotor replacement make sense?

-In many cases machining rotors can create more problems than it solves.

-GM is considering implementation of a new warranty policy that will specify replacement rather than refinishing of rotors that are worn unevenly, badly scored (ie: to a depth of .060-in. or more), corroded or are below minimum thickness.

A perfect repair or replacement of a brake rotor is completely negated if the service tech does not use a torque wrench or impact gun with an appropriate torque limiter attached to tighten the lug nuts when remounting the wheel. Not using those tools invariably results in uneven torque on the lug nuts which will *always* cause warping or lateral run out of the rotor.

The distorted rotor makes intermittent contact with the pads leading to uneven rotor wear. The thickness variation resulting from intermittent contact is what causes the pedal pulsation. Improper tightening of lug nuts is *the number one* root cause of rotor warpage on all C4s. It is also an issue with C2/3s with disc brakes, but perhaps not as critical a factor due to the thick rotors used on those cars.

A recent survey of service techs by *Brake and Front End* magazine shows rotors are being machine in 75% or more of the brake jobs being performed. This means that most service techs are conditioned to always machine rotors during brake jobs...a notion that goes back to the days of heavy disc brakes and asbestos-based pads. Many of these service techs fail to realize that technology is, indeed, changing and that rotors do not need to be serviced every time one changes pads.

Many service techs routinely "rough up" the surfaces of brand-new rotors, apparently not knowing that today's semi metallic pads need a smooth surface to be effective. That old practice became inappropriate when the brake parts industry stopped making asbestos-based pads that used to glaze rotors.

To add to the challenge, GM specifications in most cases limit runout to just .003-in. on today's rotors and 65-82 rotors ought to be held to .002 in. Precision machining of this kind also requires removal of all visible rust that accumulates on the wheel hub flange or on the hub itself because rust flakes are more than thick enough to cause future pulsation problems.

Any service tech or DIY who thinks the rotors they've worked on are machined well should put them to test using a profilometer, a stylus that accurately measures surface irregularities. Rotor faces that look smooth and ready for reinstallation are routinely shown by profilometer testing to be very poorly refinished and out of spec. Current rotors are final-machined during the manufacturing process on precision grinders to ensure proper surface finish, a finish so fine that it is almost impossible to achieve with most of the brake lathes currently in use by the service trade.

Lots of information in circulation today has predisposed many people to rotor refinishing rather than simply not doing any thing with the rotors at all or, if there is a problem, just replacing them. A 1994 story in *Consumer Reports* advises readers to "...question whether you really need new discs particularly if the car is new and the discs have not been machined before." As a result of this conditioning, many people will demand the rotors be refinished because they have been taught to do that.

C4 service manuals give specific data as to conditions under which rotors should or should not be machined and when they should be replaced. I would advise everyone to consult that information before doing anything with rotors during a brake job. That has always been my policy on brake work.

For example, my 1988 Chevy Beratta *never* in 100K miles and three sets of front brake pads ever had the rotors machined. Each time, I inspected the rotors and measured runout to find all within specs. When it came time to replace the fourth set of pads, the rotors measured under the minimum thickness so I replaced them, too, but I did not machine the rotors before installation. I simply installed new rotors and new pads. My 95 Corvette is not in need of brake service yet, but when it is ready for pads I will observe the same service procedure.

Thanks to Hib Halverson for this info.

QUESTION: I'm having a problem with my ZF 6-speed transmission, how do I repair this?

ANS: 1. Send transmission to ZF. They would require a deposit of about $500, and would tear down and inspect the transmission. They would then call you and tell you the diagnosis and an estimate of repair.

Labor rate is approx $80/hr. Repairs have run from $1500 to $4000 depending on amount of damage and parts required.

ZF America, located in Atlanta, Georgia

Mike Patterson 847-634-3500 ext 263

2. Order a rebuilt ZF through GM STO(or could be SPO). Cost of their rebuilt is $3300 and $1850 for the core (a deposit until they have yours back)

3. Or go to an independent contractor with ZF that sells both new and rebuilt units - Melrose T-Tops in Illinois.

Melrose T-Tops Inc.
4310 Ellwalk
Courtland, Ill. 60112

Thanks to Dave Wheeley for above info.

Also you can contact one of the 5 regional distributors listed below:

ZR51 Performance- is a ZF 6-speed repair shop. Bill Boudreau is very knowledgeable in the repair and care of our 6-speed transmission. His costs are ~60% that of GM/ZF. He also offers fast turn around in as little as 3 days. For ZR-1 Net "Gold" members Bill is offering 10% off any parts used in the repair of your transmission. For more info contact Bill Boudreau at (602) 740-6277 or send him an email at:

 bill777@inficad.com

ZR51 Performance
5612 East Almeda Court
Cave Creek, AZ 85331
1-602-740-6277

Here's a great article on troubleshooting your ZF transmission.

FORTE'S PERFORMANCE TRANSMISSIONS
474 Moody Street
Waltham, MA. 02453
1-781-647-1530

CONSOLIDATED TRANSMISSIONS
5606 Carder Road
Orlando, FL. 32810
1-800-578-8726

MIDWEST TRANSMISSION CENTER
40312 County 8 Blvd
Zumbrota, Minnesota 55992
1-507-824-2012

ALL TRANS PARTS
1814 N.E. Argtle Street
Portland, Oregon 97211
1-800-237-8601

Another great source for parts and ZF repairs. White Racing Products has ZF parts as well ZF rebuilds.

For more info contact Kurt White by sending him an email at KNJW1@aol.com

QUESTION: How do I enter diagnostic mode for my A/C and how to get digital readout of various engines parameters and settings?

ANS: To enter diagnostic mode, push and hold the fan up arrow and down arrow at the same time until the LCD shows -00. You are now in diagnostic mode and may select any parameter using the up and down arrows. To see the value for that parameter, press the fan "auto" button.

Note: A minus sign on the display range means to add 100 to the value displayed. So -155 actually is 255.

Thanks to Marc Randolph for this info.

QUESTION: Does moving the MAT sensor help in performance?

ANS: The idea behind relocating the MAT sensor is to delay the onset of air temperature based spark retard. Put in simpler terms the software that controls the spark advance has a modifier applied to it after a certain air temperature that reduces the amount of ignition advance the engine runs.

This is done so in high ambient temps you don't run into wouldn't, what you are doing by moving the MAT sensor is to increase the chances of running the engine into detonation.

The favorite trick by some tuners is to also move the temperature threshold in the software as well and increase the det sensor limits which means you are running very close to the det borderline all the time.

If you live in an area like the southwest for instance, with this set up you run a greater risk of engine damage, LT5's are not prone to piston damage from detonation but do blow head gaskets due to denotation and in extreme cases damage the cylinder head face (I can send you some nasty photos if you like!!!).

In short, lots of people do but personally I wouldn't, the problems far out way the gains. Five years of development and testing decided that the MAT sensor should go where it is!

Thanks to Geoff Jeal for this information.

From Graham Behan on same subject:

The control system, part of which controls the spark timing, of the LT5 is a relatively simple thing by today's standards only 32 K as opposed to over 2mb on some trucks. Basically there is a 8 inj table and a 16 inj table for the spark control along with several algorithms that add or subtract spark depending on sensor inputs. One of these sensors is the manifold air temp sensor (MAT). Since a high inlet temperature can lead to a change in the detonation characteristics of a given mixture we monitor the air inlet temp and modify the commended ignition advance accordingly. Now with a relatively high compression ratio engine, such as the LT5, the rate of applied retard for a given temperature increase is somewhat aggressive. The sensor location in the air horn is not an ideal place, since the surrounding heated metal can soak heat into the sensor and give a false high reading, thereby causing a false retard condition. This placement was largely driven by the philosophy that the LT5 should be a complete assembly by the time it left the production facility, there are many sound reasons that support this approach; checking system integrity and reducing installation time at the vehicle assembly plant to name but two. Now a more representative place to pick up the actual intake air temp is somewhere that is relatively thermal insulated from the heat source i.e. the engine, yet is still in the inlet air flow. So the relocation of the MAT sensor to the filter housing is quite a valid solution since it is measuring inlet air and the high temp protection is in place. However modifying the software to minimize the control system response to a high air temp signal is, in my believe not such a valid solution. Since the protection algorithm is put there for a reason, high inlet air temps = tendency to detonate. With the advances in the modern engine management systems engines are now calibrated closer to the detonation limit of the fuel. Given this it is correct say that the LT5 was calibrated conservatively and could tolerate more ignition advance under some circumstances, as the track results show measure a more representative air temp and effective spark advance is increased Limit system authority and the same can be said (at what potential cost). So why not get a representative measurement increase spark advance and let the system take care of itself in the way it was designed. PS this cal was set to run on 89 Oct (RON+MON/2) fuel and be safe with 87, i.e. some detonation allowed but to be controlled by the Knock sensor, up until the 91 MY when a Premium fuel recommended logo was put in place on the gas filler.

QUESTION: Does installing a lower temperature thermostat help performance?

ANS: The EMS software contains many tables and functions that are temperature based, the warm up fuel table for instance has an input directly from the temperature sensor to give fuel enrichment on start and warm up.

The calibration of these functions and tables is based around the stock thermostat so lowering the temperature that the engine would normally run at has a detrimental effect on the calibration and long term the health of the engine.

The engine may appear to produce more power running at 65/70deg C (sorry cant work in F!!) as the engine is probably receiving more fuel through warm up enrichment (I would have to look at the source code listing to be sure - can't remember where the enrichment runs out).

There are numerous temperature references in the software this is only one example. Apart from the software angle there is also the mechanical disadvantages of running too cool.

The cooling system itself is marginal, always has been. If the car is being used for high speed work in high ambient temperatures the best solution is to improve the system itself.

Hope this makes sense.

Thanks to Geoff Jeal for this information.

QUESTION: I have an oil leak somewhere?

ANS:  Those of you who see oil leaking on the right side of the engine need to check the oil pressure sensor under the oil filter. It leaks out the top/connector end of the sensor. The only way to check this is to clean the area with simple green then drive the car to trace the oil. I would suspect this long before I would suspect the oil pan. (Been there done that).

The ZR-1 has three sources of leaking oil sensors. Two in the right front top of the engine listed in the manual and one located under the oil filter, not listed in the manual!!

The part #s are:

The one in front is the oil gauge pressure sensor updated part # 10243574

The one below that is an oil temp sending unit part # 10096136

The one located under the filter is #25036935

From my experience the first and third above are prone to leaking and the one under the filter is not easy to change. There is a special socket you can buy to change these sensors (I bought mine at Pep Boys) that helps but if you have a large hand you might want to enlist some help.

Thanks to Tyler Townsley for this information.

QUESTION: My oil temperature sensor is a 3 terminal sensor but the shop manual shows only 2 terminals?

ANS: The correct oil temperature sensor P/N is 10096136 ($20.90 list), and this is a 3 terminal sensor. The '90 shop manual does not show this correctly - the 3 terminal sensor was new for '90, and has been used since then. The "C" terminal provides a variable resistance to case ground for the IP temperature gauge, while terminals "A" & "B" connect to the thermistor used by the ECM. ("A" = black wire to ECM internal ground, "B" = dark green wire).

Thanks to Ted M. Godett for this info.

QUESTION: My ZR-1 gear shift knob rattles?

ANS: Remove the center console and the large plastic piece by the shifter. This will give you access to the shifter. Pull the shifter boot up and out of the way. (I did not remove the boot, just pulled it up and out of harms way) On my '91, there are four chrome nuts on the shifter plate. All four nuts were very loose, causing a very loud rattle upon acceleration. I tightened all four nuts, pulled the shifter boot down, replaced the plastic piece, replaced the center console, tightened all screws in and around the shifter/console areas.

Thanks to Greg Moreland for this info.

QUESTION: How can I get a copy of my window sticker?

ANS:  Contact Triple A Enterprises at 317-875-7635. Or call or call the National Corvette Museum at 1-800-53vette or visit their web site at http://www.corvettemuseum.com

QUESTION: What is that keyhole below the radio for?

ANS: This key is known as the "power key" or "valet" key as it's referred to sometimes. In the off position the ZR-1 only puts out about 1/2 the hp by disabling the second set of fuel injectors, valves and what could be described as your secondaries from coming on. A sort of safety feature that GM felt was necessary when you have drivers who are unfamiliar with driving automobiles with that much HP.

QUESTION: What kind of Dyno results should I see if I Dyno my ZR-1?

ANS: It will depend as no two LT5 engines are the same but here are some results from one Dyno shop. Remember these numbers reflect rear wheel HP which is what really counts.

QUESTION: When I removed my LTPWS from my wheels I get a code 99?

ANS: When ever you remove all 4 wheel sensors you will get a code 99. It may not appear right at first and can go up to 200 miles before it turns the light on and sets the code, but it will happen.

There are 2 things that can be done and both require removing the DIC.

One is to remove the light in the upper right hand corner of the DIC and the other is to unplug the module. This can be done by using a hook to fish the connector out to where you can unplug it.. The module is attach to the right side of the speedo cluster and can be seen through the hole behind the DIC. It has a pink wire and a black wire going to it, after 91 there is a third wire, tan.

Thanks to Jerry Watts for this info.

QUESTION: It seems my Bilstein shocks are leaking, does this mean they are bad?

ANS: Bilstein Gas Pressure Shock Absorbers, due to the extremely high pressures exerted on the oil chamber, must use a seal which is extremely tight. To prevent deterioration of this rod seal due to high temperatures and wear resulting from the friction between the piston rod and seal, a self-lubricating seal is used. By design, a small amount of the shock absorber oil is allowed to pass by the seal onto the piston rod, thus creating a constant film of oil on the rod. In fact, approximately 10% of the total oil capacity of the shock absorber is intended for this purpose.

After long periods of service, this oil will create a film on the shock absorber body. The appearance of this film of oil is normal and should not be taken to indicate a defective Bilstein Shock Absorber. This gradual oil loss will not affect the performance of the shock absorber over its service life.

Bilstein Gas Pressure MacPherson Strut Cartridges operate in a completely unique manner compared to standard types. The large diameter, metal portion visible inside the dust cover of an installed cartridge is actually the body of the shock absorber, not the piston rod as on standard types. This part of the Bilstein cartridge passes through sliding bearings thus requiring very high quality grease between the sliding bearings inside the cartridge.

This grease is, of course, picked up by the moving body chamber. The appearance of this lubricant is normal, and in fact essential for the proper operation of the shock absorber cartridge. This should not be misconstrued as oil on a piston shaft, as is the case with the standard cartridge designs.

This also should serve to stress the importance of proper installation of the supplied dust covers, as contamination of the lubricating grease by road dirt or water will seriously affect the proper performance of the cartridge.

BILSTEIN CORPORATION OF AMERICA

Terry Kane
Technical Manager
Detroit Office
313-354-8181

QUESTION: Why is my clutch pedal at a different height than my brake pedal?

ANS: About a month ago, I noticed the car was hard to shift, especially getting into gear at rest.

Additionally, the car would start only with the clutch pedal hard on the floor. At first, I suspected air in the system and shortly thereafter I suspected a component problem in the hydraulic clutch system. Anyway, though I read in the service manual that clutch pedal travel was 6.25 inches after measuring mine and finding it about four inches, having nothing else to compare with, I decided such a disparity between actual and specified was a misprint in the manual...after all, the pedal didn't look bent and I verified there was nothing preventing the clutch pedal from coming up the the 6.25 inch level. The fact that the car wouldn't start except with the clutch was pushed real hard, ie: the clutch switch was not closing, should have been my best clue that the manual was, in fact, correct and there was no problem with air or components.

Once I had bled the system profusely, replaced the master and the slave, the pedal was still low but the car was now shifting ok, but clutch engagement was just off the floor...still not right. Obviously, there was some air in the system but not enough that the system would have failed to work with proper travel.

For the twelfth time, I slid the seat all the way back, put the tilt wheel up and crawled in the foot well on my back. This time I just lay there with the shop light studying the clutch pedal and thinking. I finally decided that the pedal had to have been bent somehow, but where? As I looked up, I noted that the pedal arm, makes an "s" bend about halfway up to the pivot. That is the only place it could be bent such that the pedal is two inches lower than the brake.

I got 15 responses to my query about clutch pedal height. The interesting thing was the wide disparity in heights. Only six cars, mostly 95s and 96s had the pedals at the same height. The others were all over the place. I had five with the clutch was higher and three with the clutch lower. The largest disparity was one inch. Three cars has clutch pedals one inch *higher* than their brakes.

My conclusions are that 89-up, C4 clutch pedals can bend and can do so fairly easy. Those who have clutch pedals that sit more than one inch lower than the brake, should pull the floor mat out and measure clutch pedal travel. If it is 5 inches or less, you could have a problem with clean clutch release and shifting due to lack of pedal travel. You should first verify there is no problem in interference due to wiring or other stuff snagging the pedal under the dash. Then verify that the clutch master piston is coming all the way back and resting against the retaining ring at the rear of the cylinder. If those tests are passed, consider that your clutch pedal may be bent.

As for Barney the SLPT with a 4.5-in. pedal travel, the clutch pedal comes out this week. I am sure it is nothing that a big damn pry bar and a vise will not fix.

The next question is, how does a pedal get bent. Well, hydrolocking the clutch system by mistake during bleeding didn't help, in fact, it twisted the clutch pedal such that I have had it out once already to fix that. However, the height problem was pre-existing. I suspect that, because I bought this car used and I am familiar with its history, that a significant amount of aggressive driving (i.e. pounding the clutch during quick shifts on the drag strip) in the past may have bent the clutch pedal over time.

The clutch pedal bending over time is more evidence that one need consider all sources of shift trouble before convicting the lubricant.

Lastly, this clutch pedal height survey along with my own experiences tells me C4 owners can change the position of clutch engagement within a range of maybe as much as two inches. I am sure a slight bending of my pedal such that travel is 5-in. rather than 4.5 will reestablish enough travel for good drivability. However, My legs are such that raising clutch travel back to 6.25 inches will be even better.

Thanks to Hib Halverson for this info.

QUESTION: I hear a lot about after market brakes, how do they compare?

ANS: Product Comparison Table

QUESTION: Are head gaskets a problem on the LT5?

ANS: The LT5 is prone to head gasket failure if allowed to get really hot. This is because of the extremely small clearance between the coolant passage and the combustion chamber at the lower side of the cylinder. Simple solution. Don't run it hot (250+)

Thanks to Jim VanDorn for this info.

QUESTION: Can the ZR-1 dual mass flywheel be machined?

ANS: The dual mass flywheel can not be machined and this is mentioned quite clearly in the service manual. The flywheel will have numerous blue spots and other wear marks but if the surface is smooth and ungrooved, leave it alone. Replacements are $800 and are un-necessary. These blue spots occur within a few minutes of operation of a new clutch anyway.

Thanks to Jim VanDorn for this info

QUESTION: I want to buy a ZR-1 but I've heard so many stories about cost of parts and other issues?

ANS: Many new potential owners of ZR-1s have the same fears. They hear stories about how expensive it is to repair a ZR-1 or actually the LT5 engine. As it's true that the LT5 engine can be expensive to repair if you have a total failure, it is also true that it is rare for these engines to have serious problems. If for some reason you should have a blown LT5 engine you can get them rebuilt at a cost from $10,000 to $20,000 depending on who does the work and what needs to be done. Dealers may quote you $25,000 or more for a new engine but you can find engines on the market for a lot less. If you are really going to lose sleep over this than you should either walk away or try and find a late model ZR-1 that is still under warranty.

Remember this is a limited production high performance automobile, less than 7,000 were built and one of the fastest production automobiles in the world. Also remember that when you could buy a new ZR-1, sticker cost was $70,000. Today you can buy used ZR-1's with very low mileage for as low as $30,000.

Parts availability and costs also seem to be another factor in the decision making. Stories are that parts are hard to find and cost a lot. First remember that 85% of the ZR-1 is the same as any C4 Corvette. The only thing different about the ZR-1 is the engine, outside the body being wider and bigger tires. So most parts are available and prices are very fair. It's when you get inside the LT5 engine that prices get high and may be a little harder to find. But also remember that many ZR-1 owners are having their engines modified to push more HP and most of these cars are low mileage when they hit the performance shops. What this means is there is a stock pile of low mileage used ZR-1 parts out on the market.

Keep in mind you're not buying a mass production automobile. ZR-1's were built for those people who wanted something unique and very fast. I promise you that if you drive one you will want one. It's the best bang for the buck you can buy today on the market. It's a car you can drive in traffic with the radio and AC on and a car you can take straight to the track and beat the hell out of. Like any car that is taken care of properly you will see a 100,000 miles and more.

Believe me when I tell you most ZR-1 owners are not rich, we make payments and sacrifice a lot to own these cars but to rephrase a famous saying, "they can have my ZR-1 when they pry my cold dead fingers from around the keys!"

QUESTION: Bilstein shocks are expensive to replace. Is there a way to rebuild them?

ANS: If anybody out there is thinking about purchasing new shocks for your Corvette, you may want to think about having your factory Bilstein shocks re-valved. {Most C4s came with Bilstein shocks from the factory} Bilstein will rebuild/re-valve your shocks, per your instructions, for $55.00 per shock. The turnaround time for the rebuild/re-valve service is about 2 weeks. This service is performed at Bilstein in San Diego, CA. I too was flabbergasted by the dealer price. Trying to find Bilstein products at retail (or a salesman with any insight on performance shocks) was not easy. Bilstein has a web site at "http://www.bilstein.com". Great information available in the motor sports section on how to shock tune your chassis and trouble shooting the car on the track. Bilstein has a complete dealer list available at the phone number listed below. I have found the staff very pleasant and eager to help. They also sell the Bilstein FX3 Controller, Slalom & Road Race chips, and front/rear actuators for selective ride Corvettes.

Bilstein
8845 Renco Road
San Diego, CA 92121
619-453-7723
Fax 619-453-0770
http://www.bilstein.com

Thanks to Greg Moreland for the info.

ADDITIONAL INFO when dealing with FX3:

1. If you see multiple codes (more than 2), clear the codes and start over. I suspect there is a software bug in the controller which causes the "all codes" indication.

2. If you have to drive the car with a system fault, disconnect the indicated actuator and manually adjust the affected shock to full firm because you might have an actuator stuck in the soft position.

3. The replacement actuators are very pricey (try over $400, can you say "gouging"?) from GM, but you can find them for $150 to $200 (new) from Delco/Bilstein distributors. Direct from Bilstein costs more.

4. The FX-3 actuators are not rebuildable, but

5. Bilstein will continue to rebuild shocks for the foreseeable future at a much lower cost than for new ones.

6. The code reader and manual sold by MidAmerica for about $90 was designed by Gordon Killebrew and has proved to be a great addition to my tool supply, and it now goes with me on every trip. It's almost as good as a shop manual, but

7. You really need a shop manual for the diagnostic trees.

8. Front actuators are a common part from 1989 thru 1995 as are the rears, but front and rear are not interchangeable. The ZR-1 shares these parts with the narrow car.

Thanks to Glenn Breitung for this update.

QUESTION: My ZR-1 stalls after a few minutes or when it reaches 177 degrees?

ANS: One annoying problem I had that may be useful to someone, is that the car would stall and not run after reaching 177 degrees on the temp gauge. The problem was consistent and repeatable. As much as I hate instructions, I picked up the service manual, and found the problem in about ten minutes. I found the paragraph (under LT5- engine won't start) that said "At 176 degrees F, the secondary fuel pump relay de-energizes" it kind of made me think....Hmm.. If the primary fuel pump croaks, and the secondary pump doesn't run after 176 degrees, then maybe that's the problem.. Fortunately, I had a spare fuel pump/ float assembly laying around and the swap was made. I have never been so happy to see the number 178 before. Summary....If you have a problem with your ZR dying after it warms up (symptoms are the same as running out of gas) check and see if the magic number where it dies is 177 degrees.

Thanks to Ed Simmons for this information.

QUESTION: What's in the '93-'95 owners kit?

ANS: You receive a standard Corvette owners manual, Corvette flashlight, Corvette pen and 2 1/2 x 3" Corvette note pad, LT5 power curve chart, standard tire and warranty booklets, a black ZR-1 keychain in '93 owners kit (no key chains in '94 or '95)  and ZR-1 video that closely resembles the base model version with "some" additional ZR-1 specific info in a leather zippered case with Corvette and emblem in the center and bowtie and ZR-1 embossed in the lower right corner.

QUESTION: Are the 6-speed transmissions in the ZR-1 the same as in other 6-speed C4s?

ANS: No, the unit in ZR-1s is specific to the car and unlike those used behind L98s, LT1s or LT4s. The difference is longer input shaft (~$550) and longer guide tube (~$110). This conversion requires unit disassembly (~4 hours labor). Also there are two different units (torque rating) used in the ZR-1: 1990-93 1/2 and 1993 1/25-95.

QUESTION: Are the roof panels stamped with a VIN number?

ANS: Yes, the factory did start numbering the see thru roofs, because they were a high thief item. Look on the left front corner of the frame, if it is an original factory top it should have the same last 8 numbers as your vin number on the dash.

Thanks to Jerry Watts for this info.

QUESTION: What is this ZR-1 "Black Motor I hear about?

ANS: The Black Widow Project
In December 1992, at the 40^th Anniversary Corvette Show in Palm Springs, California, Doug met Gary Cline the LT-5 Project Engineer for MerCruiser. At first they chatted. Then, as the evening grew longer, they started talking about ideas. Rippie listened and thought. He asked, "Whatta you think?" and "What if?" more than a few times. They agreed that the best idea of all would be to do more than talk.

"I think anyone who’s tops in his field wants to see what he’s created be all it can be," says Rippie. Cline, other MerCruiser LT-5 project engineers, and Lotus engineers who were involved in the project knew their engine was capable of higher performance than it had powering the ZR-1 Corvette. Doug Rippie was a kindred spirit. It was decided to work with him to produce a special LT-5 engine, the DRZ-500, also known as the "Black Engine" because each of the DRZ-500 engines produced was painted with special black paint and the "Black Widow" engine, from the nickname given by Jim Van Dorn to the eight DRM-converted ZR-1 Corvettes that are powered by DRZ-500 engines, one of which he owns.

The DRZ-500 engine resulted from the cooperative effort of Rippie, Cline and other MerCruiser engineers, Graham Behm of Lotus Engineering in England and Tim Holland of Lotus Engineering USA, and Chevrolet’s blessing. There were four versions:

Total qty was 8:

QUESTION: I understand a second design head was introduced in late production engines?

ANS: The latest two head designs had recast pockets for providing better oil retention for the cam timing chains. This reduced even further the possibility of chain rattling during startup, providing better dry start lubrication, especially after long periods of the engine not running. These heads were are referenced as the "A.L. Dunn Cylinder Head, First Design and Second Design" ( The latest Second Design Lotus Part Number was 550.4005.878A-RH and 550.4005.877A-LH) These second design heads were a design year change occurring sometime just before the final '95 designated engines were completed. The model year change specification documents were "ECH=3D 550.2680; MY=3D95A; ECA=3D1.0285". These heads did not include the CNC machining of the port runners when installed on the motors. The improved port matching technique was the same as the first design heads. GM's part numbers are 10228866-RH and 10228865-LH (Service part numbers are 10168655-RH and 10168654-LH. These are the numbers used internally for the construction of the motor).

The first design Dunn head included the CNC machining and better port matching technique to the manifold for '93-'95 applications, and also the revised oil retention pocket.

Again, the second design heads did not have CNC machined runners, and the casting walls were thicker. GM argued there was very little difference in flow rates between the cast runner and CNC machined runner sets of heads. Most of the horsepower increase in stock applications, anyway, was supposed to be from better port matching. When replacing heads, GM may inadvertently send one of each rather than a matched pair, i.e., both machined or both cast runner. These heads are not uniquely distinguished by GM part number, so be careful when you buy to at least check for comparable runner treatment. The second design Dunn head is not uniquely part numbered from the first.

Note: the thicker casting walls on the second design heads might be advantageous for machining out to even greater flow rates than achievable with any of the other head designs?

The high flow head work done early on by the fellows at Mercury consisted of refinements on the cast runners and port matching done by hand. From this work, patterns were developed for the horsepower bump work marketed through the rebuilders. This early modification work was all subcontracted to the two fellows at Mercury, Scott Skinner and another fellow named Greg ( I can't find his last name), returned and then installed on customer motors.

Thanks to Mark Broin for the above information.

Additional info: You can check your 1995 ZR-1 to see if it has A. L. Dunn heads by looking at the side (near the front) of the passenger side head (look in with light just beside the right front shock, high on the side of the head). If the plate covering the cam tensioner has three black bolts ... two on top about 1 1/2 inches apart and one on the bottom you have A. L. Dunn heads. Birmal heads have two bolts, one on top and one on the bottom.

Thanks to Paul Dehnert for the info.

QUESTION: How come you can't buy just the cam covers without the heads?

ANS: One reason LT5 cam covers are not available separately is that there are no cam bearings in an LT5. The cams ride directly on the head and cam cover material which, of course, is aluminum.

To set the cam bearing clearance, the cam covers were torqued to the head then align bored by MerCruiser on very special equipment designed and built specifically for that process. Because of the length of the bores, alignment and bearing clearance is very critical.

Thus, one can not simply change cam covers because the new cover will not be align bored to match the head.

This is why cam covers come with heads.

Thanks to Hib Halverson for this info.

QUESTION: How does one pop out the opening to the non functioning exhaust outlet in an early stock ZR-1?

ANS: The production Corvette mufflers with two "tailpipes" on each side are actually designed as single tailpipe mufflers. The dummy tailpipes are the result of Styling's wet dream. We have told them many times that if they put two tailpipes on a muffler it will cost us power if we make them both active. While I'm sure this isn't obvious to someone outside the business, the reason is simple: we have to pass the same noise laws regardless what the exhaust system look like. If we give up volume inside the muffler to create an additional exhaust path, we have to restrict the flow internally to have the same noise level as measured by the required tests.

So, the pipes you see with "disks" blocking them are not blocked at all; they are strictly dummy tailpipes welded to the ends of the muffler. The small bleed holes in the muffler shell were a compromise to let a little bit of exhaust out so they appear to be working. (Note: this applies to all production Corvette mufflers, not just ZR1s.)

If you drill through the muffler shell at the base of the dummy pipes, you will effectively destroy the primary tuner which resides in that part of the muffler. you won't like the result. It will create a strong "boom" between 1200 and 1800 RPM that's a real headache producer. Further, you won't improve the performance.

Thanks to Jim Ingle for this info.

QUESTION: When do the secondaries open on a ZR-1?

ANS: The secondary port throttle strategy on the LT5 is that on all model years prior to 93 the secondary port throttles will open at all RPMS at WOT, the 93 and later cars will not open even at WOT until the engine RPM is at or above 1500. The reason for this is that the 93 engine actually makes more torque on 8 injectors at the lower RPM'S than on 16 injectors. This was largely due to the revisions which were incorporated in the intake ports to aid airflow. This actually led to a slowing down of the air charge in the secondary port. The use of a more radical camshaft on the secondary profile is perfectly feasible and several engines have been modified in this manner and do show significant gains, however the use of longer durations typically leads to a reduction in the bottom end torque so this configuration would probably be best suited to later opening of the secondaries, ie keep on 8 injectors until the two torque curves cross.

Thanks to Graham Behan for this info.

QUESTION: I'm seeing a loss of platinum pads from my spark plugs?

ANS: Let me attempt to clear the air on the 41-907/41-913 issue with the ZR1 community. By the way, please pass along info as to the member composition of "Team ZR1". Please distribute as you see fit.

After the 907/913 discussion, I need to explain a few things about the AC long-life design families and their evolution. I also would like to describe the failure mechanism at work when a platinum wear element is lost from an electrode.

The 41-907 and the 41-913 are identical designs except that the 907 (original equipment) has the addition of topical compounds for anti-seize and anti-stick benefits. A graphite based anti-seize compound using an alcohol carrier was added to the thread body of the 907. Commercially known as "DAG", this compound was selected based on its' anti-seizing capabilities, minimal influence on installed torque vs. shell stretch interactions, and processing concerns. The insulator butt of the 907 was coated to reduce the potential for the silicone boot to stick to the glazed insulator butt. This compound was a Teflon polymer commercially known as Vydax and was supplied by 3M. Both of these compounds were removed from service plugs because of non-synchronous processing requirements and environmental/health concerns.

The 907 and 913 designs were from a family known as the "Dual Pad" family. This means that both electrodes had disc-type platinum wear elements welded to them. While these early 100,000 mile designs were very erosion resistant, their electric field characteristics were not optimal.

In 1996 and later production a new design family known as "Hi-Efficiency" was released. These designs addressed some of the shortcomings of the Dual Pad family in that fine-wire platinum elements were attached to the center electrodes to improve electric field and combustion characteristics. Some designs included a fine-wire element welded to the sidewire as well. Both variants included a larger cross-section side wire material with a larger bend radius (to reduce the overall length of the wire) resulting in reduced operating temperatures of the wire.

Which brings us to the dominant failure mode of the platinum to inconel interface. Basically, the weld junction fails from thermal fatigue. Reducing the peak temperatures, the rate of temperature change, and the number of thermal cycles all are keys to retaining the platinum element(s). The shorter, heavier side wire of the HE plugs runs cooler and is more stable than the lighter, longer wire used on the Dual Pad series. Centerwire temperatures increase with insulator temperatures; meaning that the center wires of "colder" plugs run cooler than those of "hotter" plugs in a given application. In general, higher specific output engines with higher BMEPs result in higher spark plug operating temperatures. Therefore, a colder platinum plug of any design family is more likely to retain the center electrode platinum element longer than a hotter plug will.

All of this leads me to make a recommendation for a service plug (unofficially at this time) for the LT5; the 41-950 AC (service package #25312442). This is an HE design used in the Northstar. It has a .050" gap (which should be retained), "2" heat range (same insulator as the 907/913), and a very durable resistor of a tighter specification. This is an excellent product with performance characteristics that are unsurpassed in the industry. There is, however, one caution. Since the plug is no colder than the original, the center electrode operating temperatures are the same. If the 1.0 mm fine wire platinum element of the center electrode is lost due to thermal fatigue the spark gap will open to .090". Demand voltage of this gap will exceed the voltage available from the coil resulting in misfire. The present solution would be a colder HE plug, but AC does not offer such a plug to the service community. A future (one year?) electrode design will offer a solution to this problem.

In general use, ZR1 owners no doubt change their plugs long before they've worn out. Owners exercising their vehicle in a performance environment may be better served by using a non-platinum design and "clipping" the side wires to 50% center electrode coverage to improve e-field characteristics or using a design having "trimmed" electrodes to start with, like the AC RapidFire product. Non-platinum plugs are available in both tapered and flat seat families in the "2" heat range grade in both standard and RapidFire designs. The R42LTS or #8 RapidFire designs are both "2" heat range plugs having tapered seats. The FR2LS and #5 RapidFire "2" heat range and the FR1LS and #9 RapidFire "1" heat range offer flat seat options. I would gap any of these plugs at .042" - .045", always using a pin type gauge.

Additionally, always remember these three things when installing new plugs:

1) Gap is important!

2) Installation torque is critical for proper heat dissipation. Tapered seat plugs should be installed at 11-15 lbs/ft and flat seats at 18-22 lbs/ft in cold aluminum cylinder heads. Reduce these specs by 30-35% if using a light coating of nickel or copper based anti-seize compounds.

3) A light coating of silicone grease inside the spark plug boot will increase the protection against arcing over (flashover).

Thanks to Mark Weaver of Delphi Spark Plug Engrg for this info.

QUESTION: EPROM & Learning Procedure

ANS: Learning Ability:

"The system has a "learning" ability which allows it to make corrections for minor variations in the fuel system to improve drivability. If the battery is disconnected, to clear diagnostic trouble codes or for other repair, the "learning" process resets and begins again. A change may be noted in the vehicle's performance. To "teach" the vehicle, ensure that the engine is at operating temperature. The vehicle should be driven at part throttle, with moderate acceleration and idle conditions until normal performance returns."

Clearing Diagnostic Trouble Codes:

"To clear any Diagnostic Trouble Code (DTC) from the memory, either to determine if the malfunction will occur again or because repair has been completed, power feed must be disconnected for at least thirty (30) seconds." (Note: If this mode is used to clear a DTC.)

"Depending on how the vehicle is equipped, the system power feed can de disconnected at the positive battery terminal "pigtail," or the inline fuse holder that originates at the positive connection at the battery. (The negative battery terminal may be disconnected, but other on-board memory data, such as preset radio tuning, will also be lost.)"

"NOTICE: To prevent system damage, the (ignition) key must be "OFF" when disconnecting or reconnecting power."

The above is from the service manual. The procedure serves much the same purpose as rebooting a computer to (re)initialize the system firmware's software parameters. This should be accomplished, as an example, whenever an EPROM is replaced. The battery should be disconnected prior to replacing an EPROM or other electronic components; one reason, amongst others, is that the EPROM, like other electronic components, is an ESDS component subject to electro-static discharge. Under certain climatic conditions, I use a wrist grounding strap when handling ESDS components.

Contrary to others, changing an EPROM is not a 5-minute procedure if done correctly and completely. Prior to repair, replacing the EPROM in this instance, I use a diagnostic grounding tool to interrogate the CCM/ECM for the presence of current or history DTCs as these codes, if present, will be lost when the battery is disconnected. I also use a scanner to determine/compare other engine management parameters before and after replacement of the EPROM.

I also plan to drive the vehicle to implement the "relearn" procedure immediately following the repair while the engine is at normal operating temperature; as such, as the first step, the engine is started and brought to normal operating temperature prior to disconnecting the battery. The second step is to remove the ignition key and disconnect the battery.

Next, remove and replace the EPROM taking care to ensure that it is evenly and completely seated and that the retainer clip on each end of the receptacle is returned to "lock" position. Once the EPROM is replaced, reconnect the battery and restart the vehicle. The A/C will default to "ON" upon restart; turn it "OFF," and also enable the secondary injectors (power key "ON"). While at idle, monitor all gauges and the DIC for "NORMAL" operation and allow the engine to again reach normal operating temperature.

Next, the vehicle should, as the service manual states, be driven at part throttle, with moderate acceleration and idle conditions until normal performance returns. Avoiding traffic congested areas, I drive about 30-45 minutes alternating between periods of moderate acceleration, using 1st through 4th gears, and periods of idle to complete the learning procedure. It is not necessary to test the rev limiter. Finally, I again interrogate the CCM/ECM for the presence of current or history DTCs, and scan the engine's management parameters for a before/after comparison.

Thanks to Bruce Wolfe for this information.

QUESTION: Are the "power keys" special or coded for each ZR-1?

ANS: The Power Keys for the ZR-1 are not special or unique to each ZR-1 (except for the 1990 ZR-1). All '90s will work with all other '90's and all '91's thru '95's will work with each other. For some reason the 1990 is different, maybe keyed different then all the other ZR-1 years.

The part numbers are as follows:

1990 part number 12505009.
1991 - 1995 part number 12508275.

Also for some reason the 1990 key is twice the price of the '91 thru '95 keys.

QUESTION: Can I put Dex-Cool in my ZR-1?

ANS: This is a letter from Ron Moser and in the October issue of Motor Trend should help.

Thanks to Al Kindler for this info.

Additional info on this subject from Hib Halverson:

I had started last month to research this subject at GM.

The first source told me that the reason the disclaimer about pre-94 vehicles was put on the packaging of GM-branded Dex-Cool, was that GM has some theoretical engineering data that said some of the components of the Dex-Cool anticorrosive chemical package might not be friendly to the silver solder used to manufacturer copper brass radiators. What's funny about that is that Corvette has not used a copper-brass radiator since 1982 and in other GM lines the copper brass radiators are long gone.

Anyway, this guy went on to say that testing work is underway now, but that started after the aftermarket version of Dex-Cool was introduced as both GM-branded and Texaco-branded products, seems to show that any damage to copper-brass radiators, if it occurs, would only happen after a time in service far longer than virtually any car would run--he threw out numbers of half-a-million miles or more.

Now, the one thing you must be cognizant of when using Dex-Cool in a cooling system previously filled with any coolant using a silicate-based anticorrosive package---which means all antifreezes other than Dex-Cool--and that is the silicate-based chemicals coat the inside of the system with a silicate "scale" that seals and protects the system. Some things in Dex-Cool, particularly the chemicals that give Dex-Cool the 5yr/50,000 mile service life factory- or fresh-fill applications, are partially degraded by the silicate-coating. Thus, when you change coolant in an engine previously filled with an antifreeze having a silicate-based anticorrosive formula, you cannot get Dex-Cool's long life. I believe GM says you can run it 2yrs/24000 miles.

I was told by another person at GM who works with coolants that a number of flushes with straight water can remove a lot of the silicate coating but he also said that these flushes must be accompanied by running the car awhile with straight water.

Bottom line on Dex-Cool is that, in engines previously filled with coolants using an antifreeze having a silicate-based anticorrosive package, it is best to use a 2-3 yr/24,000-36,000 mi. change schedule. Even though the change schedule is not as good as the factory-fill situations, that Dex-Cool is much more easy on the water pump seals makes it worth the change.

QUESTION: What about oil break in for '90-'92 ZR-1s vs '93-'95 ZR-1s?

ANS: The 90-92 engines were designed to be "run in" and operated with standard 10W30 high quality oil. The piston ring material is different from the 90-92 engines, but not the sole reason why the '93-'95 engines were shipped with and run with synthetic oil.

From Graham Behan:

"The tangential force of the oil ring changed (in '93), we always had an asymmetric barrel top and a tapered second made by Goetze from their F14 cast iron material. Once again no changes were made specifically for the change in oil (synthetic oil). Typically the engine does not reach stabilized oil economy for up to 25000 miles. By the way the tangential force of the oil control ring was actually lower on some 93 & later engines."

QUESTION: Why does the LT5 engine have two different PCV valves?

ANS: Well as in most of the stories from the early days of development it is a long'ish one. Yes the system is the way it is based partially on cost. The fresh air recirculation type of system utilizing PCV'S was the way that most GM products were and the way that the LT5 was specified. The problems with this were that with the LT5'S relatively high output coupled with the lack of internal crankcase volume the requirements for the PCV system was very different from the norm . The engine exhibits very different characteristics at part load/no load than it does at WOT, this is true of most engines but the massive blowby at no load required a very different PCV characteristic than the WOT condition. During the development process Allan Nobbs, of Lotus, came up with a variable orifice PCV valve which was well suited to the large changes in the engine. Well after the design was shown at one of our many vendor meetings it was decided that tooling a completely different valve was not on, so the system was changed to the current spec, using two valves with differing characteristics in an attempt to establish a good compromise. We can all see the results, the system actually exhibits reverse flow at WOT.

I wonder if there is an alternative that would work better?

One other way is to eliminate the fresh air recirculation and use an orifice controlled system. This method shows good crankcase depression under most engine operating conditions.

Thanks to Graham Behan for this information.

QUESTION: I've heard that early ZR-1, 90-92, exhaust manifold were better than later model, 93-95, manifolds?

ANS: For some time there has been a little confusion and a little controversy over which stock exhaust manifolds are better for power, the '90-'92's or the '93-'95's. This is probably because it is an established fact that some of the nominal power increase for the '93 MY was achieved through an improved exhaust system. Intuition suggests that the manifolds have something to do with it. The fact of the matter is, that the '93-'95 manifolds cause a loss of about 3 to 4 horsepower. This info was brought to us a while back by Graham Behan. The power gains from the exhaust system result from changes that were made to the mufflers. Graham was the release engineer for the '93 MY upgrades.

As was explained, the late model manifolds include a feature that addressed a potential problem. It was discovered that a catastrophic failure of the ceramic element in the catalyst could lead to serious engine damage if the engine ingested ceramic debris from the cats. A restriction was purposely placed in the manifold as a safety measure. I have often wondered what form this restriction took.

Over the weekend, I removed my '93 manifolds in the course of installing headers. Once the heat shields were removed, the restriction became apparent. The manifolds are a tri-y design. The collector tube is 3" in diameter. Where the tube enters the catalyst chamber there is a 1/2" deep dent across the tube. Apparently this pinch in the exhaust flow causes a venturi effect that prevents loose material from traveling upstream.

Thanks to Marc Haibeck for this info.

QUESTION: Can the starter in a ZR-1 be rebuilt?

A starter rebuild is pretty straight forward. The procedure is disassemble, clean everything, bead blast, if possible. Brushes generally do not need replacement, however, they can be obtained from Jap starter rebuilders. The 2 bearings for the armature are NSK 6000D and NSK 6200DW. The 2 large bearings in the main case are Fafnair 9104PP. Try to use a waterproof grease on the gears. Paint is Krylon #1613 semi flat black.

Thanks to Vicky E. Robinson for this info.

QUESTION: What is the best way to jack up a ZR-1?

ANS: Do not jack a C4 at the center of its side frames. If you do, the biggest risk is cracking the front glass.

There are only two places to properly lift a C4 with a floor jack.

At the front, you lift on the cross member just ahead of the engine. It is best to use a block of wood (4x6x1.5 works best) on the jack pad. Many C4s will have to have their front wheels driven up on blocks (12x2x2 works good) to get the jack under the car. Once you're up on the blocks, turn the wheels to full lock and come in with the floor jack behind whichever tire is turned in. Only floor jacks with long, low frames typical of 2-ton jacks will be able to do this. It works very well if you have the right floor jack and a block of wood.

You also can come in from the front with the floor jack but then the blocks you drive the front up on must be much higher.

At the rear, you need the "Jack-a-Vette" tool. It bolts to the jack pad and its vertical leg goes between the exhaust pipes and lifts on the rear axle housing. This method is not documented in the factory service manual but had been used in the service trade for many years and, according to the makers of Jack-a-Vette, was used at Bowling Green during the C4 era. On cars that are lower than stock, the rear may have to be driven up on blocks to allow enough room to get the floor jack and Jack-a-Vette underneath.

To support a C4 on jack stands, place the stands on either side at the front right where the frame turns inward behind the front wheels. At the rear support the areas of the frame just ahead of the rear wheels. In all cases, I use small blocks on the jack stand pads. Take extreme care to avoid crushing fuel or brake lines.

Thanks to Hib Halverson for this info.

QUESTION: What's the story on the Birmel vs Dunn heads on later model ZR-1's?

ANS: All the engines were produced substantially before the 1995 and about 1/3 the way into the 1994 production periods (i.e.., Fall of 1993). The motors were stored at the plant and assembled into the cars by some methodology known only to the guys who brought them to the line. There is no guarantee the last 1995 cars built got the latest engines built, or that some of those engines may not have found their way into earlier serial number cars. Also, some motors went to SPO for replacement or sale requests while cars were being built. As we all know, many other engines made their way into the public's hands.

So, the only way to determine if a car has A.L. Dunn heads, is to be able to recognize them when you examine the car. Vehicle production S/N is no guarantee. To see if you have Dunn heads using a mirror look for a triangular shaped tensioner cover on the passenger side heads with 3 bolts and a center adjuster that lies under the cam cover. Look for a little casting mark with a mirror just under the cam covers of A.L. Dunn heads - left of the dipstick as you look through the wheel well on the passenger side. You will see a sort of rolling scroll (a similar font is bauhaus 93 if you look in WORD or AOL) that reads "dunn" in all small letters; and then what appears to be an "l" on the left side head, and an "r" on the right side head. The Dunn casting mark is also present on the driver's side in about the same position.

Also, it is possible to get one head of each design from SPO if you order a replacement pair. They don't open the boxes when the heads are shipped to see if the surfaces are machined or cast. There is also no part number difference between the two heads. GM's rationalization is there is no performance difference.

Thanks to Mark Broin for this info.

QUESTION: Why do I see oil in the plenum area?

ANS: The breather system of the LT5 is certainly not one of the LT5's strong points, stories from the dark early days of development were akin to the striking of an oil deposit for the first time. There were many strange contraptions which were intended to keep the LT5's running, one of which was a four inch diameter tube connected to the oil filler cap, which when under wide open throttle, a column of oil would raise three feet into the air, since this would have been a severe packaging problem other solutions were sought for the vehicle. Basically there is insufficient crankcase volume and the system which exists is a serious compromise. So all LT5 engines carry a small amount of oil through the breather and it is perfectly normal to see oil in the plenum. With increasing blow by this situation will get worse, but typically not enough to cause detonation problems. In most race applications we recommended running a quart over full to minimize the effects of oil surge. Basically don't worry it typically isn't that bad.

Thanks to Graham Behan for this info.

QUESTION: Are there any durability differences between the 2 bolt '90 - '92 LT5 engines and the 4 bolt '93 - '95 LT5 engines?

ANS: For 90-92 production engines the durability target was 200 hours of GM's Corporate Durability test cycle, which consisted of cycling the engine between peak torque and peak horsepower rpm at WOT, with a 2.5 minute ramp up and down between the two speeds. For the 1993 and up engines the requirement was 400 hours on the same cycle. The biggest single improvement from the 4 bolt blocks was actually a process upgrade made at Central Foundry which eliminated porosity in the main bearing webs. When Lotus actually started to run the first 4 bolts, with cases from Dennison Foundry, they split up the # 2 & 4 main bearing webs. When Dennison went chapter 11 they moved to Central Foundry and reaped the benefits of better process control leading to less gas entrapment.

Thanks to Graham Behan for this info.

QUESTION: How do I replace the battery in my ZR-1?

ANS: 1. Turn ignition switch on (without starting engine) and turn wheels fully to the left (as though you are making a left turn). This will provide plenty of clearance to the torx fasteners at the rear of the left front wheel well. Once wheels are turned, shut ignition off and remove key.

2. Using a T30 torx head wrench, remove the top three fasteners at the rear of the left front wheel well liner. These are located just in front of the left front fender at the outer side of the wheel well liner.

3. Using a 10mm socket, remove the bolt at the rear and top of the fender. You can now carefully "tilt" the fender panel outward.

4. To provide additional clearance for the fender, use an open faced 10mm wrench and loosen the bolt at the bottom of the fender. There is a narrow slot through which you can insert the wrench. I small flashlight is helpful in seeing this bolt. Since the bolt is upside down, make sure you turn it in the correct direction to loosen and later re-tighten it. Once you have loosened this bolt a few rotations (without removing it), you can now tilt the fender outward enough to have plenty of clearance to lift out the old battery.

5. Using a 13mm socket, remove the battery hold down clamp located at the bottom middle at the rearward-facing side of the battery. There is pretty tight clearance on this, and I had the best results using an 8 inch 1/4" socket extension bar, approaching the hold down bolt from the top.

6. Disconnect the cables from the battery using the correct size metric socket 8mm. Remove the negative cable first, which is the outward cable, followed by the positive terminal cable.

7. Once the cables are disconnected, carefully lift the outward side of the battery slightly upward to lift it above the retaining nubs in the battery tray (in other words, you can't just slide it straight out). Once you have cleared the battery tray, you can now lift out the old battery.

8. Remove the battery insulation sleeve from the old battery and transfer it to the new battery (AC Delco 75-7YR).

9. Lift new battery onto the battery tray and slide it inward into place. There are some wires running down the back which are very tight clearance to the battery, so make sure you hold these rearward while sliding the battery in so that don't catch the battery insulation.

10. Reinstall the hold-down clamp.

11. Connect the negative battery cable.

12. Connect the positive battery cable.

13. Lift the fender panel back into position and just start to thread the top 10mm bolt.

14 Reinstall the three T30 torx fasteners in the wheels well splash panel. Make sure the fender panel is aligned correctly so there will be no interference with the driver's side door's range of motion.

15. Tighten the top 10mm bolt with the fender panel in correct alignment.

16. Tighten the bottom 10mm bolt.

17. Start car and be happy again ;-)

A couple of notes. On my car, the battery was definitely dead. The engine fired right up with the new battery. Also, the correct AC Delco replacement battery (75-7YR) has the condition "window" located on the wrong side (near the positive terminal), so it is not visible once the battery is installed.

Thanks to Steve Castle for writing this up.

QUESTION: What is the difference between each year?

ANS:  CHANGES AND REFINEMENTS FROM 1990 to 1995 ZR-1 / LT5 CORVETTES

1990

EXTERIOR

1) The first year front end had the same body design as the base Corvette with the distinctive black rub strip that encircled the car sporting the “TUNED PORT INJECTION” wording indents. The 3-inches-wider than base Corvette rear had a new, dynamic convex shape and all new "square" tail lights that were only available on a ZR1. The center high mounted stop light would continue as a ZR-1 exclusive through 1995 even though the 1991 base Corvette assumed the rear convex identity of the King of The Hill. But only for the ZR1, did it include widening of the doors, rear quarters, rocker panels, rear fascia, and rear upper panel. Two black 1-1/2 spacers are noticeable on either side of the license plate, between the back up lights. It is difficult to notice the 0.9” difference in length between the ZR-1 and base Corvette. The 3465 pound weight of the ZR1 is 236 more than the coupe. The ZR-1 purple tint solar-block windshield is slightly different from the base car with a larger, clear opening for "electronic garage door openers". The 1990 front and rear emblem has a Black Ring and the right hand side "Bowtie" background is Red with a Black "Bowtie" outline - Gold filled. (same as 1984-1990).

2)  In the books All Corvettes are Red, and The Heart of The Beast, there is mention that 10 or 12 ZR-1 narrow body convertible Spyders were built. Some had DR-1 on the license plate in honor of Don Runkle, the LT5 chief engineer. He was presented with a silver ZR-1 convertible with yellow interior built by ASC and Chevrolet at Bowling Green.

3) Mid-year exterior color introductions were: Medium Quasar Blue Metallic, Turquoise Metallic, and Yellow. These colors do not appear in the 1990 dealer catalogs.

INTERIOR

Leather Sport seats with 2 lumbar controls, one on each side of the seating surface.

DRIVETRAIN

1) The ZR-1 engine, designated LT5, is all aluminum for the block and cylinder heads, has 4 overhead camshafts, 32 valves, and is a 350 cubic inch V8. The HP rating was 375 at 370 ft lbs of torque from 1990-1992 and 405hp at 385 ft lbs of torque from 1993-1995.

2) Trans gear ratios: 2.68 / 1.80 / 1.31 / 1.00 / 0.75 / 0.50 : Reverse = 2.50 : [610 (Nm) / 450 ftlb. torque capacity]

3) The 1990 – 1992’s used one piece exhaust manifold/cat assemblies.

4) From the start of production in 1988 (MY89) to 01/01/89, all 6-speeds had a 3.54 axle. After 01/01/89 the ZR-1’s received a 3.45 axle.

5) As stated in the dealer catalog and ZR1 owner’s kit book, the 1 to 4 lockout (CAGS) on the 6-speed transmission was part of a strategy for meeting E.P.A. fuel economy requirements. 1990 through 1994 requirements included the following: Coolant temp: at least 120 degrees; M.P.H. - 12 to 19; Throttle Angle - Less than 35%.

6) A few of the first 1990's sported steel half shafts while later production was aluminum. The half-shaft was changed during the 1990 model starting with VIN # 800621. Known VIN #’s = 208 / 410 /

7) The early 1990 LT5 engines prior to VIN #913 came with "screw worm drive" radiator hose clamps. These were changed to "spring type" later in the Model Year to correct a possible coolant leak problem at the radiator hose attachments due to torque loss. A new Service Kit P/N 10157951 became available which included 6 new radiator hoses and 12 new "spring type" hose clamps to correct this potential problem. Known ZR1NET member VIN#’s = #357 / #410

8) Early 90 ZR1’s have an additional "Air Foil Bar/Wing" bolted to the radiator air intake opening, just above the center front spoiler that is painted the same color as the car. After 1990 models, this is not reported.

9) Some early 90 ZR1 owners report having glass headlight bulbs (the rest of us have plastic).

SUSPENSION

Selective Ride Controls

DIMENSIONS

http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1)  Manual AC (C60) was standard, with electronic control AC (C68) as an option. Only 124 ZR-1’s were produced with manual AC. Known Production Numbers are: #418 / #713 / #969 / #1040 / #1766 / #2086 / #2838/ #1039 / #1562 / #2431

2)  In the first half of the 1990 model year, the CD radio came with a lock-out feature (Delco-Loc II). “Loc II” was printed on the face plate. The owner was instructed to program a six-digit number into the radio. Whenever the radio lost complete power, the number had to be used to unlock the radio, otherwise the CD and cassette players were locked. If the numbers were lost or forgotten, the radio could be re-programmed by the dealer.

3)  A big “pizza box” ZR1 Owner’s kit was sent to some. This contained a leather portfolio case, copy of the window sticker, driver’s manual, coffee table sized ZR1 book, keychain, video, and emergency key case.

INSTRUMENTATION

1) The early models had a shift light (separate from the 1 to 4 light).

2) There are two different types of DLCs on ZR1s. 90-93 uses the 12-pin DLC
seen on all GM cars since 1982.

3) There was no low oil light option on the 1990 model, but the bulb position was in the DIC (Driver's Information Center).

WHEELS

The exclusive, directional mag-type rear wheels and tires are 1-1/2” wider.

1991

EXTERIOR

1)   Curiously, some yellow 1990 and 91 Corvettes were photo-chromatic - (Not on purpose...). If you were to leave an object on the car in the sun and remove it later, the paint would be darker under the object. Sunlight actually changed the color of the paint – but it changed back later like photo chromatic sunglasses do. The paint was reformulated when discovered to eliminate this "unique characteristic".

2)   It's rumored that on 4/23/91, a special color 1991 ZR1 was made for a dignitary - WA-9795 Green/gray.

3)   New horizontal front fender "gill" panels.

4)   In 1991, ZR-1 maintained its own unique personality with the CHMSL stop light over the glass hatch - and the wider rear stance. All base models of Corvette now had the ZR-1 style convex rear with square tail lights and a new wrap-around, streamlined front end with color-coordinated rub strip around the body.

4)   Only the 91s had the 24 hour endurance champion sticker from the factory on the bottom left side of the rear hatch glass. (The L98’s have it too.)

5)   New version of the crossed flags emblems. The 1991 emblem has a Black Ring and the right hand side "Bowtie" background is Black with a Red "Bowtie" outline - Black filled. (1991-1996)( except 1993-40th anniversary -Chrome Ring).

6)   New “delay” feature meant power is continued for the entertainment system and power windows up to 15 minutes after the ignition key is turned to OFF, or until the driver’s door is opened.

INTERIOR

1) Interior was pretty much the same, but the mid-dash sweep was a bit less squared.

2) Seats were almost identical except the 91 included only one built-in left side lumbar control switch per seat, while the 90’s seats had 2 controls - on left and right sides of driver’s and passenger’s seats.

DRIVETRAIN

1) The dealer brochure incorrectly says that Tuned-port fuel injection was replaced by Multi-port fuel injection in the 1991 – it was 1992.

2) Cylinder head Valve oil seals were added.

3) LT5 cam cover emblems change from red background to black.

4) In '90 only the intake valves had seals. In '91 and up seals were used on all of the valves.
NOTE:  If an exhaust valve stem gets too dry it could stick or seize.  The '90 exhaust guides can be machined to accept seals.
 

SUSPENSION

1) Steering Overall ratio went from 15.6:1 to 15.7:1.

2) New Bosch ABS IIS

3) Among the options were heavy duty suspension components so the ride could be adjusted from firm to very firm, rather than from soft to firm found in earlier systems

DIMENSIONS

http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1)  Manual AC went away after the first year and electronic control AC became standard.

2)  The C-note horn was replaced with an F-note beginning with the 1991 model.

3)  A big “pizza box” ZR1 Owner’s kit was sent to some. This contained a leather portfolio case, copy of the window sticker, driver’s manual, coffee table sized ZR1 book, keychain, video, and plastic emergency key case. The only difference from the 1990 was the video and the coffee table book contents.

INSTRUMENTATION

1) The power-key default was changed to OFF with each restart of the car. The actual key is different from the 1990 key. The Full Power light was relocated on the Drivers Information Panel from the Upper Right Hand side for the 1990, to next to the Full Power Key for 1991.

2) Manual AC went away with electronic control AC becoming the standard.

WHEELS

1991 The new design “turbine-look” aluminum mag wheels appeared to be moving even when the car was standing.

1992

EXTERIOR

1) The ZR-1 badge emblem was added to each side front fender.

2) Exhaust tips changed from the two per side, to one large rectangular per side.

3) New colors - Black Rose Metallic, Arctic white, Bright Aqua Metallic, Polo II Green Metallic. Deleted colors were Old Polo Green (less blue-ish), Turquoise, Old White (identical color), Charcoal.

INTERIOR

1)  Saddle leather interior was discontinued, and Light Beige was the replacement. Blue leather discontinued. Light Gray replaced the slightly darker gray interior color.

2)   Steering wheel horn buttons changed from gray to black.

3)  An option that was standard in the earlier RPO ZR1 package was dropped 1/2 way though the 1992 year. The power passenger seat RPO AC1, which had always been packaged into the ZR1 option was pulled and had to be ordered separately.

4)   The little triangle buttons below the console seat switches for the 1990 and 1991 models is discontinued.

5)   There are reportedly 12 White ZR1’s with white interior, one White/White is # 502. Plus there is one Red exterior/White interior '92 ZR-1 with VIN #392.

DRIVETRAIN

1)   Acceleration Slip Regulation (ASR) is introduced.

2)   92-up cars use a two-piece exhaust manifold design where the cat bolts to a flange at the exhaust manifold outlet. Also the design of the exhaust manifold was changed to prevent back-flow under deceleration.

SUSPENSION

Suspension tuning change- reduction front spring rate from 96.2 N/mm to 75.4N/mm,

reduction in rear spring rate from 39.9 N/mm to 33.0 N/mm.

DIMENSIONS

See http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1)   The master cylinder bore was increased. In addition, the front brake calipers were changed to increase the brake pedal height.

2)   The big box ZR1 owner’s kit is discontinued.

INSTRUMENTATION

No changes

WHEELS

Tires went from Goodyear Gatorbacks to Goodyear GS-Cs.

1993

EXTERIOR

1) A 40^th Anniversary Ruby metallic ZR-1 package was available only in 1993 with 245 ZR1’s made (5 were pilot-test cars).

2)  Bright Red became Torch Red, Yellow became the reformulated Competition Yellow code 53

3)  A special order for Dark Red Metallic (75U) with black leather was reportedly applied to only two cars. One of those two '93s is VIN #0062. The color is very close and could be confused with the "Dark Ruby Red Metallic" reserved for the 40th Anniversary Edition. There is a 40^th dealer poster error of a convertible in the plant with code 75U doors.

4)  In '93 the plant switched to a new clear (two-component polyurethane) that was typically applied thicker than the previous flavor... The smoother “orange peel” appearance is due to the paint technology change. The 2 component paint has a longer wavelength (wider) peel than the previous 1-component, which was quite short (tight).

5)  New Styrofoam inner bumper absorbers were a midyear change. The cars were slightly overweight by EPA standards, so this was one of the changes made late fall or winter 93.

6)  For the model year 1993 the BG plant began putting VIN's on the glass tops.

7)  The Bowling Green emblem under the hood was replaced by the Mobil 1 emblem on Sept. 28, 1993, according to factory info. But, 93-40th Anniversary ZR1 #381 has the Mobil 1 emblem.

8)  The `93 offered an Arctic white interior for ZR-1's.

INTERIOR

1)  In 1993 GM once again included The power passenger seat AC1 as part of the RPO ZR1 option.

2)  The interior seat design was slightly changed to a wider, more comfortable style and entry – exit became easier. In 93, all seats of every color had the 40th anniversary emblem embroidered into the headrests.

3)  Torch red interior replaced bright red.

DRIVETRAIN

1)   Horsepower increased for the LT5 engine to 405HP @5800RPM and 385lb. ft. of torque at 5200RPM. The increases came from Head work; Revisions to the valves; Revised exhaust cam timing; a reduction of restrictions in the exhaust system and an electrical - linear exhaust gas recirculation (EGR) system for improved emission control; Revised injector housings and injectors; Altered plenum for increased flow; Smog Changes; Reduced rotating mass; 4 bolt cylinder case; Revised PROM; Oiling system improvements; Platinum Spark Plugs; Synthetic Oil.

2)   The part # was changed on the ZR-1 transmission from 10186865 to 10255122 starting on VIN #800232 in the 1993 model year. Trans gear ratios stayed the same. The most significant internal changes found in the ZF S6-40 540 Nm version is the increase in helical pitch of all the drive gear teeth to be more quiet. Included in the 400 lb ft change, the 2nd, 3rd, 5th and 6th speed gears went to a crimped spline-fit method of fastening the synchronizer clutch body to these speed gears.

3)    Wiring change that the 93 and newer Vettes had, which was to have the clutch switch moved from the high current starter solenoid circuit to the coil side of the start relay circuit.

4)    SEQUENTIAL PORT FUEL INJECTION

SUSPENSION

No change

DIMENSIONS

http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1) New ABS IIU

2)      Sometime between '93-94 model years the advanced computation power of something called the "P8" ECM first came into existence in the ZR-1. A full blown upgrade to the earlier 8 bit microcomputer, AKA the "P4" design. With the later cars, LT5 engine RPM could now be resolved into +/-1 rpm increments. Prior to 1993, ZR-1 ECMs could not resolve any better than +/-25 rpm using the "P4" CPU architecture.

3)      From 1993 on, there are only four grease zerks on the entire car- upper and lower ball joints.

INSTRUMENTATION

The 94 and 95 cars use the 16-pin "OBD2"type DLC. The pin designations are not the same. They are located differently and use numbers instead of letters.

WHEELS

Although the same in design as 1991- 92, the 1993's wheels had a different surface appearance achieved by a flat machining on the fin tips.

1994

EXTERIOR

1) Two new exterior colors were available, Admiral Blue and Copper Metallic. The Copper did not make it the whole year due to problems with color match -116 were built when the color was killed; and Medium Quasar Blue Metallic was discontinued.

2) In 1994 two one of a kind ZR-1's were built. One was an Admiral Blue with Red interior and the other was a Competition Yellow with Red interior.

INTERIOR

1)  Interior revisions included addition of a passenger-side airbag and knee bolster (and removal of the instrument panel glove box), new seat and door trim panel designs, finer-weave carpeting, "express down" driver's power window, and a redesigned two-spoke airbag steering wheel.

2) With sport seats, a single set of power assist controls for both seats was console-mounted. Also, individual motors adjusted the lumbar support for sport seats and these controls (and the side bolster control) were relocated from the seat to the console for 1994. The leather “hand” changed from a smooth texture to a rough, pebble patina.

3)   The tire jack was relocated from the exterior spare tire well to an inside compartment behind the passenger seat.

4)   White interior is discontinued.

DRIVETRAIN

No change

SUSPENSION

No change

DIMENSIONS

http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1)      Air conditioning systems were revised to use R-134A refrigerant, a non-ozone depleting CFC substitute.

2)      On the owner’s Video, Dave Hill states there are over 280 small refinements or improvements for 94/95.

INSTRUMENTATION

New white instrument graphics turn to tangerine at night.

WHEELS

New, non-directional spoke mag type wheels were introduced.

1995

EXTERIOR

1) New front fender side vents reminiscent of the golden age 1958-61 fender side coves. (also a little like the 1973 to 82 side cove)

2) A new exterior color, Dark Purple Metallic, was added, but 1994's Copper Metallic

and Black Rose Metallic were deleted

INTERIOR

1) Sport Seats had stronger "French" seam stitching

2) Out of sight are numerous Velcro straps to reduce rattles

DRIVETRAIN

1)  The 6 speed manual was redesigned by replacement of the reverse lockout with a high-détente design for easier operation.

2)   RE: The 1 to 4 lockout on the 6-speed. In 1995, these requirements were reduced to the following: M.P.H. - 15 to 19; Throttle Angle - Less than 13 Coolant temp: at least 120 degrees.

3)   Added the latest anti-lock/traction control (ABS/ASR-5) system.

4)  Aluminized Stainless Steel exhaust.

5)  Possible A. L. Dunn heads in the last few (estimated at 130) ZR1’s produced. Some have mistaken the non-triangular cover having 2 bolts with center screw as being 3 bolts. There is also a little casting mark you can see with a mirror just under the cam covers of A.L. Dunn heads - left of the dipstick as you look through the wheel well on the passenger side. There is sort of a rolling scroll (a similar font is bauhaus 93 if you look in WORD or AOL) that reads "dunn" in all small letters; and then what appears to be an "l" on the left side head, and an "r" on the right side head. The dunn casting mark is also present on the driver's side in about the same position.

6)  New plenum flow work is reported, but needs definition.

7)  ABS controllers have a manual brake fluid bleed fitting on the side of the controller, in the well behind the driver seat.

SUSPENSION

No change

DIMENSIONS

http://www.zr1netregistry.com/ZR1_dimensions.htm

ACCESSORIES

1)      A drip-tube was designed into the A-pillar weather-strip for improved water intrusion control.

2)      A stronger radio mount installed for less CD skipping

3)      Windshield wiper arms were redesigned with revised contact angles and higher contact force to reduce chatter at all speeds, and lift at high speeds.

INSTRUMENTATION

No change

WHEELS

No change

Thanks to Randy Schulkers & Jerry Watts for putting this together.

QUESTION: I understand there are some differences in transmission gears and torque in late MY ZR-1's?

ANS: The following is an explanation from ZF regarding the HELICAL gears and gear noise. I emailed my question to ZF Ind., as to my concern over ZF gear noise when in first......I received several responses from the ZR-1 Net regarding my concern, and they seemed very plausible. However, I decided to ask ZF about the noise and the comparisons. This is what they said:"

"Dear Marshall,

You have been mis-informed. All S6-40 transmissions installed in the C4 Corvette contain 100% helical gears. In fact, all of the gearboxes ZF produces for passenger car applications contain helical gears, the primary purpose of which is to increase gear contact ratio and thereby minimize gear noise.

There is one major difference between the model year (1989 - 1992) and (1993 - 1996) C4 Corvettes - the contact ratio for the later years was further increased in order to reduce the gear noise. There, however, was a very slight reduction in torque capacity of the gearbox (from 610Nm to 540 Nm) when ZF increased the gear contact ratio in the later year transmissions.

The noise you hear in 1st gear is commonly termed "1st gear growl". This noise is inherent to the design of the 610 Nm gearbox and in no way is detrimental to the reliable function of the transmission and your ZR-1. With the increased gear contact ratio in the 540Nm gearbox, ZF also was able to reduce the "1st gear growl".

Thanks to Marshall D. Vernon and ZF for this info.

Additional Info on the ZF:

Another note to remember is that if you have a ZF 6-speed which is mid '93 or newer, 2nd gear nitrous bursts will eventually loosen the 2nd speed gear mounted synchronizer clutch hub. This spells probable catastrophic damage after 50 - 150 juice cycles. ZR51 Performance can modify the weaker 540 Nm spline fit hubs of these gears so that the separation will not occur ever. We Tig (digitally controlled) weld a narrow bead over the spline fit producing a much more durable ZF 6-speed unit. This is a very important thing to remember when considering who to choose for rebuilding/modifying your ZF S6-40 6-speed transmission.

Thanks to Bill Boudreau from ZR51 Performance for this info.

QUESTION: Is the AC compressor in the ZR-1 the same as in the other C4's?

ANS: No, the AC compressor in the ZR-1 is a Nippondenso, similar to the one used on L98 Corvettes, but smaller in displacement. The L98 compressor is 12.7 cubic inches, while the LT5 is 10.0 cubic inches.

QUESTION: What is the weight of the LT5 engine?

ANS: The LT5 engines weighs 741 lbs. including shipping crate.

Here are some other weights:

L98 - Auto 431 lbs, Manual 592.2 lbs
LT1 - 452 lbs
LT4 - 1003.5 lbs
LS1 - Auto 457.6 lbs, Manual 497.2 lbs
LS6 - 497.2 lbs

QUESTION: Did GM build any right hand drive ZR-1's?

ANS: No, GM never built any right hand drive ZR-1's. However there are several out there in the world that have been converted. For example almost every American car shipped to Australia are converted.

This info came from Colin Wolf:

1. About 95% of all American cars on Australian roads are converted. This includes ZR-1's and C5's. Corvettes that are not converted are basically show cars or special interest cars. If you were to offer a left hand drive C4 (including ZR-1) for sale in Australia, it would be regarded as a project car for conversion, and not a drivable car suitable for registration. The price you would obtain would reflect this.

2. Australian laws vary from state to state. However, in all of the most populous states on the east coast, you cannot obtain a full vehicle registration for a left hand drive vehicle. You can obtain a classic registration (or similar), which allows you to drive on public roads to motoring events or to workshops in your vicinity. Traveling interstate requires special permits. South Australia, Western Australia and Northern Territory are more relaxed but have only small numbers of Corvettes. The laws have changed just in the last year in Queensland to allow cars over thirty years old to remain LHD and be road registered.

3. Conversions from LHD to RHD are very common, and have been carried out for more than fifty years by many companies on all manner of American and European cars. One small part of the conversion scene is Corvettes, where about ten major companies do most of the work. This includes C5's and less technical conversions such as the basic rack and pinion C4's and even less technical again C3, C2 and C1. Our largest local Corvette converter does about 150 cars a year, including Vipers, all model Corvettes including C4 and C5, light commercial trucks, mainly GMC etc.

4. The job of converting a ZR-1 includes converting the steering plus accelerator, clutch, brake, mirror the dashboard, and completely rewire the car. Most companies will have a complete set of fiberglass molds for fire wall, floor pan, the many dash board components, air conditioning and ventilation ducts etc. These are all finished to match the original ZR-1 finishes. The list goes on to carpets, handbrake, decals, upholstery etc. As with all jobs, the devil is in the detail. Things which separate the conversion of the interior are the correct mirroring of the arm rest controls for windows and door locks, the mirroring of the side which the center consoles swings from, correct functioning of air conditioning ducts etc etc. Steering column stalks are not mirrored usually and this can be confusing for a few miles. And yes, foot room is a big factor.

5. The ZR-1 rack and pinion steering cannot be inverted, because the pinion would be in the wrong place. You need to find a suitable rack and pinion set from another car, which when rotated will approximate the mirror placement of the pinion. The route for the steering shaft is tortuous, and too large an angle at any of the universal joints will produce some startling non-linearity in the steering. Steering feel and responsiveness is always a big issue.

6. There are other road worthiness factors, such as the orange rear turn indicator lights, the need for additional side indicator lights and the need for Engineering compliance with Australian Design Rules. The present, fairly strict system of licensing of converters is being further upgraded next year to include quality assurance requirements to ISO 9001. Known as the RAWS (Registered Automotive Workshop Scheme), one it's components will be the prohibition of conversion and registration of vehicles with significant structural damage. After May 2003 it will not be possible have cars which are written off or have substantial structural damage resurface in Australia legally).

7. I paid about $20,000 Australian dollars for my conversion. $A1.00=$0.54US

8. Why would you do it? Simply so that you can drive your Z on the road. Would you do it if the law allowed you to drive LHD? Difficult question. A late model (C3 onwards) is worth more money if converted. You can recoup some of the investment when you sell the car. A solid axle or a midyear is devalued by a conversion, particularly no longer necessary. Me, I am comfortable with my right hand drive ZR-1, which I drive to work a few days a week and my wife drives occasionally.

QUESTION: Why do stock fuel injectors go bad and leak?

ANS: Stock injectors can experience problems, some do some don't. One common problem is leaking injectors caused by either fouling by combustion byproducts or rust inside the injector. Any ZR-1 that sees lengthy periods of non-operation, such as winter storage, may have problems with rusted injectors. You can't see the rust, because it's internal but the symptoms of a rust problem with be the same as leaky injectors due to fouling.

Another problem with the OE injectors is inconsistent flow rates. The ACDelco Multec injectors can vary across a set of 16 by as much as 10% in flow rate and it's common to see 6%.

If your injectors don't leak or have fouling problems, it is typical in a case where you're looking for extra performance to flow test and mix/match as set of stock injectors to get the flow variation down as low as possible. To do this you need to deal with a service facility that has a pool of Multec injectors to use in mixing/matching. Unfortunately, you also have to find an injector service vendor that has a large pool of LT5 injectors because of the difference between pri. and sec. injectors.

Bottom line: stock injectors will work ok but only if you have a set that flows consistently across the set and doesn't leak.

Second bottom line: a better choice are RC Engineering/Lucas injectors. They have stainless steel internals so they never rust. They typically come off-the-shelf with a 1-1.5% range in flow variation.

The rotating disc fuel metering system Lucas uses (compared to the ball-and-socket system inside the Delcos) is said to be quicker to respond to changes in injector pulse width. That improves throttle response.

Thanks to Hib Halverson for above info. .

QUESTION: Does Plenum & Injector Housing porting make a hp difference?

ANS: On the 90-92 engines, porting the housings is more beneficial than it is on the 93-95s. Porting the plenum has the same effect on both engines. If the porting is done right and you use one of the better exhausts, you'll see about 20-25hp a two-bolt motor and perhaps a bit less on four-bolt motor.

Thanks to Hib Halverson for above info.

QUESTION: What type of thermostats do ZR-1's use and at what temps do they run?

ANS: AO Engineering LT5

160° start
168° partial
175° full

Stant LT5
178° start
195° partial
205° full

OE LT5
190° start
205° partial above boiling full

Thanks to Hib Halverson for above info.

QUESTION: How do I reset the security code in my radio?

ANS:

 
1. The factory did not install a code. The owner had the option of installing one.

2. If it is a code problem, LOC should show on the driver information center (DIC).

3. You are correct about the antenna (aerial) not extending if there is a code in the radio.

4. The reason for the owner putting the code into the radio was that it made the components of the radio only workable in that car. Therefore, if the radio was stolen, it was of no use to the thief.

The radio cannot be fixed by taking it apart. The code has to be erased by a long process of entering a decoding sequence that was only available from General Motors. The dealers were not even allowed to have a copy of it. The dealer had to call Detroit and they would talk him through decoding the radio.

Since you have no way to decode the radio that is in the car, your only option is to replace the control head and receiver box with another one. Preferably not another 90. A 91 will work.

Thanks to Gordon Killebrew for this info.

ANS: You can visit one of two web site to get both keys made and a new keyfob:

http://www.streetkeys.com/

or

http://www.keylessride.com/

The Resistance Value for each Key Pellet is as follows:

1. 392 ohm (or 402 ?)
2. 523 ohm
3. 681 ohm
4. 887 ohm
5. 1.13 K ohm
6. 1.47 K ohm
7. 1.87 K ohm
8. 2.37 K ohm
9. 3.01 K ohm
10. 3.47 K ohm
11. 4.75 K ohm
12. 6.04 K ohm
13. 7.50 K ohm
14. 9.53 K ohm
15. 11.80 K ohm
 

You would need to know your "value" to get your key made to match your ZR-1.

QUESTION: What is this "Active Suspension" on the ZR-1?

ANS: For info and pictures check out:

http://corvetteactioncenter.com/cgi-bin/archives/imageFolio.cgi?direct=1984_-_1996/ZR-1/Active_Suspension

ANS: The 405 hp heads fit the same as the 375 hp heads except for the addition of dowel pins to align the injector housings. The dowel pins were added as an upgrade in '93 as part of the 405 hp porting upgrade. The 375 hp injector housings are not drilled for the dowel pin holes. For compatibility, simple remove the pins from the 405 hp heads to sort of downgrade them to the 375 hp standard.

The 405 hp heads will accept 375 hp and 405 hp spark plugs. They have dual spark plug seats.

The 405 hp heads have slightly larger exhaust ports. They probably allow +3 hp over the 375 hp heads.
 

Thanks to Marc Haibeck for the above info.

QUESTION: I heard the first year for the ZR-1 was actually 1989?

ANS: Correct, GM built 3 production 1989 ZR-1's. One went to Rick Mears, a second to Hendrix Motorsports and we believe the third is at the National Corvette Museum.

QUESTION:  Are the Exhaust systems the same on the early and late model ZR-1's?

ANS: The exhaust systems follow the same pattern. The '90 - '92 cars have the original very restrictive exhaust system. Going to a Corsa system adds 15 hp. The '93 and up cars received the benefit of the LT1 mufflers. Going to a Corsa system adds 5 hp. Here's a picture showing part of the problem with the early system. http://www.zr1specialist.com/HAT%20Web/Tech%20Info/High%20Exhaust%20Backpressure%20On%20Early%20Cars.pdf It might be interesting to note that the '93 and up LT5 exhaust system is the universal fit ZR-1 exhaust system. It will fit '90 - '95 cars. The '90 - '92 cars have a three bolt flange on the right side exhaust manifold. The '93 - '95's have a slip fit on the right side. The three bolt flange on the right exhaust manifold on the early cars is attached with a clamp. The flange can be removed. After the flange is unbolted, the '93 - '95 exhaust system will slip fit onto the exhaust manifold pipe where the flange was attached.

QUESTION: I've heard the NCM has all the ZR-1 Dyno sheets, can we get a copy?

ANS: Here is the Dyno sheet story.