Road Testing a 1991 ZR-1

For three years, 1989, 1990 and 1991, the Road&Track Specials division produced an annual called Road&Track's Corvette. All three were very high-quality publications devoted solely to Corvette and each contained several ZR-1-specific articles because of the car's significant newsworthiness in the early 1990s. Nowadays all three are highly sought after by collectors of Corvette literature.

ZR1 at Age Two: Still the King

©1991, 1999 by Hib Halverson

It is now unnecessary to use the words "world-class" to qualify the ZR1. In the "high-sports" market, there's no longer any question that this car is a major force and among American-built entries in that category; it has no match, in fact, nothing even comes close. A standard by which to judge the Chevrolet Corvette ZR1 is superfluous, because it is now a standard. It has become, unequivocally, what its designers intended all along "the King of the Hill".

A goal of the ZR1 program (during development, the project's nickname really was "King of the Hill Corvette") was a "bi-modal" automobile that could move softly, but with its performance capabilities, "carry a big stick." I'm always amazed by how well the ZR1 excels at this bi-modalism. Much of this excellence comes from a four-cam V8, a six-speed gearbox and a ride-adaptive shock absorber system.

The LT5: 375 horsepower, 5.7-liters, four valves-per-cylinder and the first engine wearing the Red-Bow Tie to break the one hp/cu.in. barrier in more than two decades. Though not the first aluminum, DOHC V8 in a production car; it is significant for the quantities in which it has been built (to date, more than 3500) and its level of refinement. The latter is a credit to Lotus and Chevrolet, who developed the LT5, and Mercury Marine, who manufactures it.

It idles so smoothly you'd think it belonged in a Cadillac. Try the now-famous "five-cent test." Park on a level surface, slip a nickel out of your pocket and, with the engine idling; stand it on edge atop the fuel injection plenum. Smooth enough for you?

The LT5 is a typical of a DOHC engine because it can be as drivable as that in any family sedan. Low-speed response is extraordinary. Ample torque is available just off-idle. Incredibly, this engine's torque curve is above 300 lb/ft. from 1000 all the way to 6500 rpm. A non-turbo, four-cam engine with the LT5's abilities has never before been in a road car.

This powerplant bi-modalism comes from some sharp engineering work. The 16 intake ports are divided into "primaries" and "secondaries". The secondaries have larger port volumes and are fitted with throttle plates. There is an injector in each port. The camshaft profile of the secondary intake lobes is more aggressive than that ground on the primary lobes. Engine management controls secondary induction system operations. The driver has a manual override in the form of the ZR1's famous "valet switch" or "power key."

Below 3500 rpm, the LT5 runs on the small, primary ports and with the mild valve timing of the primary intake cam lobes. Lower port volumes and modest cam profile ensure sharp throttle response, substantial low-end torque and efficient fuel economy. At this point, if the power key is left in the "normal" position, the engine continues to run on the primary induction system which limits the LT5 to about 210 horsepower.

Above the 3500 mark, if the power key is in the "full" position; the engine management system commands the secondary throttle plates to open and the secondary injectors to come on-line. The secondary intakes - more radical cam timing further increases power and we're done moving softly it's time to swing that 375 horsepower big stick!

Driving the LT5 for all its worth is the most fun you can have with your clothes on. It begs to be run hard between 4000 and 6500 rpm. Its sound - the snarl of 16 intake valves sucking in 11 cubic feet of air each second along with the mechanical "clattery-hiss" made by a V8 at high rpm–and its feel–acceleration that comes with a rush available from few other cars are the essence of the Corvette Mystique. Plant your foot on the floor and, if you dare, keep it there through the first five gears. At the top of fifth you'll be around the 180 mph mark.

The six-speed manual transmission is another reason ZR1 is equally a racer and a cruiser. Built for GM by Zahradfabrik Friedshafen A.G., (no wonder everyone calls 'em "ZF") in Germany, its first five gears have their ratios and ratio-spreads selected for maximum performance. The sixth gear, a long-legged 50% overdrive, is a "cruising gear" intended for best fuel economy.

The "Zed-F" transmission also is equipped with a CAFE sleight-of-hand trick called "computer aided gear selection" or "CAGS". When certain engine temperature, engine speed, vehicle speed and throttle opening criteria are met; the King's ECM closes off the second gear gate forcing a first-to-fourth upshift. CAGS exists to get the ZR1 under the gas guzzler limit. Initially, the system received some "boos" from the press, but actually; I find it acceptable. When it operates, the car is always loafing and the LT5's abundant low-end torque makes a first-to-fourth gear change easy to drive. Looking at the car's mileage; I'll take CAGS.

Under aggressive pilotage, the six-speed shines. Shift feel is delightful precision. The closest contest may be the Muncie four-speeds of twenty years ago. It is close-gated but, once you get used to that, the quickness with which you can shift because of it is welcome. This gearbox's only problem is acoustic. In neutral and first, the transmission has gear-rattle. Functionally, the Zed-F is a brilliant piece of work, but considering the king's ransom one pays for a ZR1; we figure it could be just a little quieter.

In my late-teens I had a neighbor who owned a Big-Block Corvette. All of us gear head kids on the street saw this guy as bigger than life for his thundering 'Vette and its three two-barrel, 427/435. Though the foundation of the Corvette Mystique is built on horsepower; the current platform, introduced in 1984, has gained just as much a reputation for impeccable handling. Every time I hustle the King over some choice twisties I know; afterwards, I always draw the same conclusion: people who drive ZR1s fast are bored by even the nastiest of roller coasters.

At speed, this car instills a level of confidence in its driver that few others can because its handling is predictable, has no vices and always matches driver input. The steering feel and effort are just right. The grip provided by Goodyear's Gatorbacks is substantial. Suspension tuning is ideal for aggressive driving: at high speeds, just on the understeer side of neutral and, at lower speeds with the LT5's torque, slight power oversteer, but never enough to upset the car's polished demeanor. Regardless of speed, once the car's limit is reached; moderate understeer sets in. In short, we know of no other mass produced road car that drives fast so well.

A sports car's handling must provide its driver with a high level of control or the car is really not a sports car. One of Chevrolet's objectives with ZR1 is to provide this high level of control yet have the car as comfortable as possible for driver and passenger. How well this control/comfort compromise is achieved is a pleasant surprise.

An important factor in this success is a system called the Selective Ride and Handling Package. Known by option code FX3 and engineered by Bilstein and Chevrolet, it consists of a set of shock absorbers with electrically-operated, adjustable valving and a small computer device to control them.

Typically, the higher a car's speed, the more forceful shock valving must be. The FX3 computer commands electric motors at the top of each shock to adjust shock valving in six steps according to the car's speed. The driver can skew the aggressiveness of the steps and the speeds at which they occur through the three-position Selective Ride Control switch on the center console. These ride-adaptive shocks are, without a doubt, the King's most pleasing ride and handling feature.

Brakes, does this car have brakes! Veritable retrorockets, they are indeed stop to match the go. The fronts are massive, heavy-duty discs developed for the ZR1's near-180 mph terminal velocity and rigorously tested during the '87 season in SCCA Showroom Stock racing. The package consists of 13-inch rotor/two-piston caliper assemblies. At the rear are the standard, but certainly adequate, 12-inch/single-piston discs. In combination with the Corvette's ABS, this system made for maximum braking in abbreviated distances. The car's zero-scrub radius front suspension, introduced for 1988, had the ZR1 stopping with excellent stability regardless of road surface. Lastly, we saw little evidence of fading.

The King is more than just powertrain, suspension and brakes. ZR1 must offer driver and passenger a functional yet pleasing environment. The car comes standard with every comfort/convenience option available on a Corvette. Standouts are a pair of fully-powered, adjustable sport seats and automatic climate control. Additionally, the windshield is coated with a substance which reduces heat radiation. As it also blocks radio waves, Chevrolet thoughtfully added a little uncoated rectangle at the base of the glass to allow radio signals out to your garage door opener and radar in to your detector.

However, the ZR1's only shortcomings also show up inside. The interior was redesigned last year. While its overall style, particularly the door panels and dashboard and the placement of switches and controls is a quantum leap over the '84-'89 interior; the new instrument panel is a failure. Its gauges are hard to read and are often obscured by the steering wheel.

Another disappointment is the continuing use of a Delco/Bose sound system. I have never cared for it due to lack of a speaker balance control and the fact that Dr. Bose feels all Corvette drivers like jacked-up right channel volume. It was further degraded when the interior restyle moved its front speakers from the base of the windshield (acoustically good) to the kick panels (acoustically bad). The "non-Bose" stereo in my '88 Beretta is better than what's in Chevrolet's sixty-four thousand dollar flagship car. Lastly, although there's nothing intrinsically wrong with plastic; the lack of texture on much of the plastic pieces gives the ZR1 interior a look that is not commensurate with either its royal standing or its price tag.

Okay, are you sitting down? The ZR1 is not really "a car" at all. It is a "Special Equipment Package," a collection of optional equipment that, if you write a big enough check, can be fitted to a Corvette coupe. The only pieces specific to the King are: the LT5 and its accessories, bigger rear tires, bodywork to house those tires and a uniquely-sized rear antiroll bar. The rest, while mandatory options, are also available on any other Corvette.

This may be why the exterior of the King is controversial. Other than a badge and 315/35s on the rear; you look hard to tell the difference between a ZR1 and a standard Corvette. I like that understated effect. It goes right along with moving softly, but carrying a (concealed) big stick.

However, folks on the R&T Specials staff and many others expressing opinions about the car felt, that for the sum one pays for a ZR1 and its obvious position in the automotive pecking order; the King ought to dress a bit more distinctively. Once suggestion was to make the ZR1 a specific model then fit it with the hood used on the ZR2 prototype, (discussed elsewhere in this magazine) a different set of wheels and go back using square tail lights on the ZR1 only.

Regardless of the outcome of the exterior controversy and in spite being a bit shy on interior appointments, the Corvette ZR1 is indeed the standard that other very high performance GT cars will be judged for years to come. To those supporting the competition, all I can say is, "Tough luck, guys. You can always try for "Queen of the Hill!"

ZR1-SS: King-Light Carries a Bigger Stick

©1991,1999 Hib Halverson

The Dodge Viper has been suggested as future competition for the ZR1. The Viper will be a Chrysler resurrection of the Shelby Cobra concept emphasizing brutal performance, simplicity and light weight. Standout features will be its 7.4-liter, 400+horsepower, all-aluminum, pushrod V10 and styling that recalls Shelby’s wildlife.

Viper will generate tremendous interest upon its debut in early 1992. With limited first-year production (predicted to be as little as 200 units) and the Shelby connection; those of the I-wanna-be-first set who have plenty of money will be like sharks in a feeding frenzy trying to buy the initial sale of these cars.

With introduction half-a-year a way, there's no point in guessing the Viper's acceleration, speed and handling abilities. Nor does it make sense to speculate on how successful Chrysler's entry in the high-sports market will be at that all-important control/comfort compromise.

However, after the hoopla dies out, how will Viper compare to the sophistication mainstream high-sports buyers have come to expect from cars like the ZR1, the Acura NSX and others? Will they buy a car whose refinement is reminiscent of another built nearly a generation ago? I suspect that once the feeding frenzy is over, Chrysler could be glad the Viper is in only limited production.

Regardless of how Viper succeeds, the people in the Corvette Development Group at Chevrolet are adopting a "Norman Schwarzkopf defense": prepare a merciless offense. John Heinricy, Manager of Corvette Development and Validation, and his staff are preparing a prototype, lightweight, "SS" version of the ZR1.

At present, most of the car's performance increase comes from weight reduction through: removal of air conditioning and sound system, substitution of manually-operated cloth seats for the powered leather units, use of standard front brakes, magnesium wheels, a magnesium bell housing, a Kevlar hood and a Lexan rear hatch. These and other minor reductions have taken about 350-375 pounds off the car.

A diet was Phase One of the "Snake Skinner" project. Phase Two, powertrain modification, is just barely under way. So far, the LT5's camshaft timing has been altered slightly, a low-restriction exhaust system has been fitted and a 3.90:1 axle ratio has been substituted for the standard 3.45:1 unit.

Corvette Development Engineer, Jim Ingle, has run quarter-mile acceleration tests to the tune of 12.42 sec. at 119.1 mph in the ZR1-SS. Recently, I took a racetrack ride in the car with Mr. Heinricy at the wheel. Where a regular ZR1 is working hard to make 180 mph; this prototype was already at 185 and still pulling strong. I'll guess the Snake Skinner's slightly-tweaked LT5 is generating about 405 horsepower. Phase Two will continue until the engine is at the 450-500 horsepower level.

Will a "King-Light" see production? I’m not going to speculate, but 300 less pounds and 100 more horsepower sound like fun to me!

—Hib Halverson