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We all should understand that the design and engineering of a vehicle is a long
and tedious process which involves thousands of man hours by highly skilled
engineers, and usually, an unprecedented financial investment. No one in the
world ever had a fleet of ZR1 test vehicles (other than GM and it's affiliates),
therefore, it is wise to say that usually, only the tried and proven systems
make their way into our production vehicles.
You might notice I said "usually"...
Imagine for a minute, what it must take to design, engineer, test, and
certify an automobile! The breakage characteristics of glass, the effects of
air bag (s) deployment, fuel economy, the crush effect of the hood under
impact, etc., etc., etc. It's fairly easy to assume that every square inch
of a vehicle and it's systems go under the closest scrutiny.
Because of this, several things occur as a result. First, naturally the
price goes up. Second, various and numerous considerations are given to cost
saving measures which of course include the substituting of lesser priced
items for the more expensive ones. This can clearly be seen with some higher
priced "luxury" cars receiving, say, a real wood treatment on the dash where
a lesser priced model may receive an imitation wood appliqu? In that case,
our $65,000+ ZR1's should have the best of the best , right?
Well...almost....
Remember that government requirements including safety, emissions and fuel
economy play a major part in the finished automobile. You might remember
back in '93 when the first ZR1's came in too heavy which resulted in some
quick engineering fixes (Styrofoam bumper absorbers) which were later used
in all regular production Corvettes. These requirements, while improving
certain specific details, may not be beneficial for optimum performance or
longevity.
The bottom line is this. The combination of cost saving techniques and
government requirements have left at least some level of improvement to many
areas of the production automobile, especially a "high performance" car such
as the ZR1. In the next issues of the Legend, we will be exploring and
discussing many areas which may benefit from at least some level of
modifications from stock. In these cases, we will attempt to focus on the
levels of enhancement aimed at the daily street driver, but also go as far
as the weekend track car. All of these changes will come with a price in
dollars but may also effect durability, driving comfort, or everyday
drivability. Remember, these changes are personal opinions and observations
based largely on years of research, personal experience and customer
feedback.
Starting out... Many of you have considered keeping your ZR1 in relatively
stock condition with the exception of possibly making small changes which
can be put back to stock at any given time. In fact, as the owner of both
one of the most exotic rides (The Weekndr), as well as a pristine 500mi 40th
ZR1, it is easy to see (and appreciate) both sides of the fence. Because of
this majority, we'll start out with the simple, easy to do enhancements and
later progress to the more major changes. After all, minor modifications is
exactly how most of us started out...
Exhaust Systems
By far, one of the most popular modifications is to the exhaust system which
is one of those areas heavily controlled by the Feds. Noise is a form of
pollution and is therefore highly controlled by the EPA. Of course, most of
us also know that an exhaust system can play at least a slight role in an
engine's performance but there are other factors to be considered as well.
Sound and appearance are also enhanced by an after-market exhaust system and
an exhaust system is easily changed back to stock if the need arises.
Contrary to most advertisements, the LT5's exhaust system does not harbor
huge amounts of hidden horsepower within. The simple fact according to
MerCruiser's own dyno testing was that an inch of exhaust back pressure is
worth approximately 3 horsepower (the earlier 90-92 systems yielded
approximately 5-6 inches back pressure). Subsequent testing by after-market
tuners, however, revealed that the LT5 responds favorably to at least some
back pressure.
There are several viable reasons to install an after-market exhaust system.
1-Change of exhaust tone
2-Appearance
3-Climate/Corrosion
4-Performance
The system you choose depends on your personal taste but remember, ALL are
considerably louder than stock. The louder the more horsepower but remember,
a 10-15 hp increase is all that you will achieve in benefits from a stock
engine from any system we've tested to date.
Many of you have purchased systems only to remove them later because of
"intolerable" increased resonance at cruise speeds. We highly suggest using
these three criteria when considering an exhaust system purchase.
1-Find one you like the sound of.
2-Find one you like the appearance of.
3-Find one you can afford.
Partial listing of some of the better known Exhaust Systems for ZR-1s today:
Headers
Many of you have heard rumors of huge horsepower gains to be had with the
installation of after-market headers. Here are some facts. First, Federal
law dictates that removal, disconnection or otherwise tampering with an
emissions control device on a street driven vehicle is a crime punishable by
fine and/or imprisonment. Removing catalytic converters falls under this
jurisdiction. However, if the vehicle is used as an "off-road vehicle", the
various laws governing such devices does not apply.
The combination of headers and an appropriate exhaust system will yield an
approximate 25 horsepower to the stock LT5. Headers will require the
disconnection of the AIS (Air Injection System) and will also require a MEM-
CAL change. Drivability will be effected with a noticeable backfire between
shifts, especially during cold operation.
Partial listing of some of the better known Headers out there for ZR-1s:
PROMS
Proof of GABBS as stated on bold print in the GM service manual: "ALL
GENERAL MOTORS VEHICLES ARE CERTIFIED BY THE UNITED STATES ENVIRONMENTAL
PROTECTION AGENCY AS CONFORMING TO THE REQUIREMENTS OF THE REGULATIONS FOR
THE CONTROL OF AIR POLLUTION FROM NEW MOTOR VEHICLES. THIS CERTIFICATION IS
CONTINGENT ON CERTAIN ADJUSTMENTS BEING SET TO FACTORY STANDARDS."
The LT5 is controlled by an Electronic Control Module (ECM) which relies on
sensors designed to monitor it's functioning. Data is received and
adjustments made every millisecond the engine is in operation. These
adjustments are dictated by the Memory Calibration assemblies or MEM-CALS
installed within the ECM which contain Programmed Read Only Memory. Hence
the terms "PROM's" and "chips".
As per the service manual: "This engine has controls to reduce exhaust
emissions, while maintaining good driveability and fuel economy."
Notice it doesn't say "while maintaining the best derivability or fuel
economy." Factory MEM-CALS are made as safe as possible in order to reduce
customer complaints and extend durability (which also reduces warranty
costs). In addition, federal regulations mandate that all engines be made
capable of operating with oxygenated and alcohol enhanced fuel, and the use
unleaded regular gasoline. How is this accomplished? A knock sensor monitors
or "listens" for a frequency of sound then relays the "knock signal" to the
ECM which in turn retards the spark timing drastically and immediately. This
can be as much of a severe reduction as 30+ degrees! The problem is, in many
cases, knock sensors relay faulty signals to the ECM causing a major
reduction in performance. We've seen many cases where cars surge noticeably
as a result of this problem.
All PROM programmers use their own formulas but most include many of the
same functions. Disconnecting the Computer Aided Gear Selection and
enhancing coolant fan operation are common benefits of an after-market
MEM-CAL. Other benefits include fuel and timing calibration changes and
quicker secondary throttle operation. In conjunction with one programmer, we
have also accomplished an extensive re-writing of the spark retard addresses
as well. Again, a MEM-CAL change is easily done and easily un-done in less
than 10 minutes.
Performance Proms for ZR-1s:
Air Filters
As we've previously discussed, the K&N filter is a very popular replacement
and although it flows air only as well as a clean AC stock filter, it will
begin to exceed the AC filter's capability once the AC begins to dirty.
Another asset of the K&N is that it is a cleanable, reusable filter.
Anyone who races knows the performance advantage of cool air into the intake
system. Most of you have already noticed the remarkable difference in the
way your LT5 operates in cooler temps than in warmer. Cold air systems were
actually tested briefly by GM during the early stages of development.
Although gains were seen in horsepower, the concern became water ingestion
under severe climate conditions. In theory, the cold air "box" is actually a
duct which pulls air from further front area of the radiator inlet than the
stock air filter housing. The downfall is that if the vehicle is subjected
to large amounts of water (or puddles), it may ingest the water causing a
multitude of problems, with some being catastrophic.
The systems which aim air directly into the induction system may use a scoop
installed in the front facia license plate area. This is an ideal location
for an air intake, however, several problems come as a result. First, the
system requires cutting (thus weakening) the frame cross-member which is the
major support for the entire front body group. Second, the unobstructed
airflow also allows debris or water to directly contaminate the filter or
even proceed beyond in some cases.
Special Note: The combination of the three bolt on
enhancements list above (exhaust, MEM-CAL, and free flowing filter) can
result in an estimated 15-18 hp gain in certain power ranges depending on
the vehicle.
Performance Filters:
Brakes
Although equipped with air cooled 13 inch rotors, the ZR1's brakes leave a
lot to be desired. With just a few harsh applications from higher speeds,
the brakes begin to fade and rumble. The most popular street upgrades
include changing to an after-market reinforced factory caliper or simply
purchasing the 1996 Corvette front brake caliper available on the Grand
Sport models. These factory calipers are not only stronger than those
originally installed on the ZR1, but they look terrific especially through
the 5 spoke wheels. Also recommended are the replacement of the rubber hose
brake lines to those of stainless braided steel. When refilling and bleeding
the brake system, the use of a high performance brake fluid (i.e., Castrol
SRF) can also help achieve positive results.
High performance brake pads are readily available in a variety of compounds.
Basically, the better the pads work, the dirtier and noisier they are. That
is, the harder compounds make more noise when applied and produce much more
brake dust which tends to coat the wheel. Also, the harder pads will wear
the rotors significantly faster than stock pads.
For the more track oriented enthusiasts there are a number of complete brake
packages available all the way up to full competition packages. These
packages range from $2,500 to $6,000 and vary greatly depending on
manufacturer. In some cases, the front steering knuckles must be modified to
accommodate the larger calipers, only selected wheels will clear the
calipers, and certain rear brake upgrades require the parking brake be
removed. Others, have a custom park brake package available for a mere $750.
If you are going to drive aggressively, you'll certainly need a brake
upgrade.
Companies that offer Brake packages:
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