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We Test Yet Another of Chevrolet's Nasty Prototypes

©1991, 1999 by Hib Halverson

Wide open throttle.

Sixty-five hundred rpm.

Fifth gear...we were moving pretty god damned fast! My adrenaline pumped and my pulse raced. Hell, we were going ballistic at any second!

The beefed-up LT5, its howl barely quieted by some little-assed race mufflers, was primal scream therapy for believers in the Corvette mystique.

The Manager of Corvette Development himself, John Heinricy, was driving. His eyes were riveted on the rapidly nearing end of a four-mile long straight. His hands clenched the wheel in the racer's three-and-nine o'clock grip. His right foot was buried.

I stole a peek at the speedometer in time to see 185 come up. "This," I thought quickly, "is almost as good as sex!" Such was my first ride in the ZR1-SS.

"Super Sport," or just "SS," always signified a Chevrolet with a higher level of performance than the standard unit. Over the years, the Red Bow Tie guys have applied those letters to race cars, prototypes and even production models. The first time it was used was in 1957 on the Corvette SS.

Initially, I heard of the ZR1-SS on a trip to Michigan in December of last year. I was interviewing John Heinricy for an article for Corvette Quarterly. One day over lunch, he explained the ZR1-SS which is part of two Corvette development programs:

1) Research into weight reduction. The Corvette's weight will become a significant issue in the mid '90s. If this is not addressed; because of resulting decreased fuel economy caused by the addition of extra weight to meet new Federal Motor Vehicle Safety (MVSS) legislation; the car may become eligible for the "gas guzzler" tax and that won't fly with GM's policy of no guzzlers. Without weight reduction and with new MVSS pieces; the only way to keep Corvettes out of guzzler would be to gain fuel mileage by decreasing engine power and/or changing axle ratios.

Guzzler is unacceptable to GM management and reduced performance is unacceptable to the Corvette Group as well as we who buy their cars, so weight reduction is the alternative. The net result will be weight the same or hopefully a bit less than it is now. This allows the remainder of the car's fuel economy "window" to go to increased power, which, trust me, is definitely a possibility.

The first phase of this experiment is to take weight out of an existing car and see what effect that has on acceleration, ride and handling. That's where the ZR1-SS comes in.

2) A little-known (at least 'till now) project called "Snake Skinner" which, strangely enough...brings us to the Dodge Viper, a car that's been suggested as competition for the ZR1 and is Chrysler's resurrection of the 1960s Shelby Cobra concept emphasizing brutal performance, simplicity and light weight. With limited first-year production and the Shelby connection, after its introduction in early 1992, those of the I-wanna-be-first set with plenty of money will be like sharks in a feeding frenzy trying to buy the initial sale of these cars.

After the hoopla, how will Viper compare to the sophistication mainstream buyers in the "high-sports" market have come to expect from automobiles like the ZR1, the Acura NSX and others? Will they buy a car whose refinement is reminiscent of another built nearly a generation ago?

Regardless of the speculation on those issues that is undoubtedly going on amongst GM's marketing weenies, John Heinricy wanted to study a Corvette of similar concept...just in case a Chevrolet response to the Viper becomes necessary.

As these two research programs involve weight reduction, it made sense to use one prototype for both. An ample supply of '89 pilot cars was left over from the original ZR1 development program, so he appropriated one of those as the basis for the effort.

The first step in building a ZR1-SS was to consign several heavy accessories to the scrap heap. First to go was the air conditioning and the Delco-Bose sound system followed by the low tire pressure warning system and the spare tire. Lighter, base-level, manually-adjustable, cloth seats were substituted for the ZR1's leather, powered units. Stock wheels were pitched for cast magnesium Dymags. A standard flywheel replaced the heavier dual-mass unit and a magnesium bell housing was used instead of the stocker. At this point, the car weighed about 250 pounds less.

Once "King Light" had been "Jenny Craiged"; its LT5 was put on steroids. This was done in two phases. The first advanced the existing engine's camshafts slightly, removed the catalysts and fitted the car with Walker Dyno Max racing mufflers. Horsepower went up to about 405.

This was the Snake Skinner when Heinricy gave me the almost-as-good-as-sex demo at a Midwest testing venue two days after our lunch meeting. However, more work was to be done, so I agreed to secrecy back then in exchange for a full Vette road test six months later. Fast forward to May 1991...

Late spring afternoons at the GM Desert Proving Ground (DPG) in Mesa, Arizona are always pleasant. The days are longer, but temperature is still tolerable. Sunsets on the Superstition Mountains to the east are an exquisite sight. The ZR1-SS, another 100 pounds lighter and with the "phase two" motor was parked at the edge of DPG's acceleration test strip sitting for photos. It seemed a bit weird (maybe it was those Superstition Mountains, eh?) shooting this car. It was as if its Royal Badness, King Light, didn't "like" being parked..."Snake Skinners are runners not lookers." was the message. It's white paint was a sinister contrast, too, as this car was anything but virginal.

The ZR1-SS had been trucked out to Mesa for the winter so Corvette Project Coordinator, Scott Leon, and his crew could finish the car. Its backlight had been replaced with plexiglass in an aluminum frame. The stock hood had been switched for a light-weight, aftermarket, Kevlar unit from Toledo Pro fiberglass. The factory headlight assemblies were nixed and their doors fixed in place. "Mini-Quad" headlights and turn signal units, both from the Pontiac Grand Prix GTP, were installed where the stock turn signals and fog lights usually go. The rear compartment doors behind the seats were replaced with a Lexan panel.

The engine was now a special unit supplied by the manufacturer of the LT5, the MerCruiser Division of Brunswick Marine Power. All modifications were aimed at increasing airflow. The cylinder heads were ported and polished then fitted with more aggressive camshafts. The secondary throttle plate hardware was discarded and the injector housings between the intake plenum and the heads were siamesed. The plenum's outlets were siamesed to match and its interior was modified for increased volume and improved airflow. Lastly the sizes of the throttle body's two main barrels were increased.

The engine's lower end is plenty strong and was run as is. Special assembly procedures were unnecessary as LT5s are essentially hand-built engines already.

After the installation of the new motor, four-into-one, tuned headers from Morrison Motorsports were added and the exhaust system center resonator was removed. The ECM software was updated to work with the new motor and its rev limit was raised to 7500 rpm. After this round of engine tweaks, the Snake Skinner had a 425 horsepower punch.

In addition to the engine modifications, the stock 3.54:1 rear gears were exchanged for a set of 3.91s. S-Compound, Goodyear ZR Eagle tires were fitted to the Dymag wheels and the software used by the ride-adaptive shock absorbers of the FX3 Selective Ride and Handling Package was altered slightly. Otherwise the ZR1 suspension and brakes were left alone. Lastly, the stock fuel tank was replaced with a unit having slightly more capacity and special baffling to prevent starvation at low fuel levels.

Scott Leon, a true Corvette enthusiast in that he pays attention to ascetics as well as performance, felt the car needed a couple of class touches. He installed four-louver fender vents from the Chevrolet Raceshop's Corvette Aero Kit and he added a set of 1992 LT1 exhaust outlets.

The other reason we were on the acceleration strip at sunset that evening in May was to get some good air for a few quarter mile passes. One thing about King Light is that with 3130 pounds, 425 horsepower, 3.91 gears and street tires, launching is a trick. I made six passes and still couldn't get it right...but I had a hell of a lot of fun!

Fire up the ZR1-SS and it's immediately apparent that this is not a car for the faint-of-heart. It's exhaust note is assertive, the idle has a race motor lope and the throttle response is so crisp as to be almost too quick. Nice guys don't drive cars like this. As I sat waiting for the engine to warm, the car's sound and feel had me daydreaming...

Somehow, we've gotten away from one aspect of the Corvette mystique: raw-edged, hard-to-handle power. Maybe there should be a ZR1-SS, i.e.: A Corvette for hardasses. Just maybe Chevrolet's "deproliferation movement" has gone too far towards techno-wizardry and mandatory option packages. Between 1985 and 1990, Corvette sales dropped 11,000 units and '91 may prove to be the worst sales year in two decades. Something needs to be done. Maybe we need to go back to a lot of choices in Corvettes...something for everyone: those who want the look, but can afford little more; those who want the performance, but can afford little more; and those who want it all. This daydreaming stuff was getting too complicated.

Anyway, sitting there in the Snake Skinner listening to the rumbling LT5 was definitely a deja vu: I closed my eyes for a second and could see, almost touch, the thundering L88 that a friend owned back in 1969...

I rolled up to the start line, brought the revs up to 2500 then, sidestepped the clutch. Yo! What a rush. The beefed-up motor revs very quickly producing plenty of wheelspin if you're not ready. Right away you gotta lift a bit. In a fraction of a second; I banged the rev limiter at the top of first gear. I shut off right there, mashed the brakes, then backed into the start line again.

The lag of the digital tach was such that, in first gear, to shift at 7400 you must do it when you see 6200. The one-two shift comes so quick ( I walked the tire marks and found the gap about 60 feet out) that, on the first two runs, reacting a bit slow; I tagged the limiter both times. The next four, I managed to get it right.

Even then, making a hard pass in the Snake Skinner depends on launching with a careful balance of rpm, wheel spin and shift point. But, hey, you gotta grab hold of that snake before you can skin it!

My best, though only an average performance, was 12.36/116.8. With darkness approaching, I put Scott Leon in to see if one who'd driven the car a lot could do better. He did...to the tune of 12.22/118.6. Bottom line: this car is quite nasty in a straight line.

That morning we used this same strip and DPG's vehicle dynamics pad for some additional tests. On the skid pad, the car, expectedly, due to its weight, sticks well. We averaged 1.01g and I felt the car could have done even better, but a byproduct of the King Light diet plan was increased ride height. A higher center of gravity may have affected skid pad performance a bit. The only modification not performed in time for our test was the installation of different springs that would set it to the proper level.

In the slalom, again, light weight was an advantage. Additionally, the car was balanced with less understeer. This slight looseness is a plus in the slalom. Lastly, the car felt crisper in the constant, transitional handling situations characteristic of slaloms. This was partly due to less weight and the better response of the S-tires.

Not all of my impression of this car came in the controlled, proving ground environment. The next day, Scott Leon and I took it on a 75 mile ride and drive over public roads. The first part went up Arizona State Highway 88 into the Canyon and Apache Lakes area northeast of Mesa in the Tonto National Forrest. It's a great road loaded with plenty of twisties linked to short straights mixed in with elevation changes.

Doing AZ88 in the Snake Skinner was a sporting driver's delight! The car's crispness in transitions and more neutral balance combined with good predictability to make it easy to drive near the limit. On the short straights, power and gearing had it a rocket ship. In fact, squeeze the gas a bit too soon or too hard exiting a turn–you got wheelspin and power oversteer, but then, that's what driving a real fast Corvette is supposed to be: a bit of a challenge that...separates the real Corvette drivers from persons with just big wallets.

The asphalt part of Highway 88 ends at a little village called Tortilla Flat that's about 30 miles northeast of the Grounds. There is a small restaurant and bar in Tortilla Flat whose main claims to fame are walls papered with dollar bills (according to local history, the place burned down a few years back–must have been a hell of an expensive fire!) along with cold lemonade and some of the best chili anywhere. Scott Leon, a veteran of this establishment, described it, "Hey, you guys from L.A....most of the chili you've eaten comes out of a can and is seasoned with smog. This stuff...this stuff, here, is chili for serious professionals!" Indeed, it was chili...only more so.

After lunch, we drove into Mesa to see what the Snake Skinner was like in a more civilized setting and it proved to be reasonably friendly. Throttle response and acceleration were great from stoplight-to-stoplight and in passing. The exhaust note was not loud enough to be annoying or attract the attention of the local constabulary. I like cloth seats over leather in warm weather. The car never ran hot and drivability was generally quite good. On the downside, I wish Heinricy had left the stereo–doesn't have to be a Bose (which I dislike anyway) just a standard Delco-Electronics unit will do. When you can't drive fast; you need rock'n'roll to keep you occupied. The lack of air conditioning was not a big problem. Most of the time the windows were down. In the heaviest traffic, however, I found myself wishing the current platform had floor vents–you know those things you pulled in an old big block car when your feet got hot? Lastly, the plexiglass backlight had about as many distortions as the does the copy you read in other Corvette magazines. Seriously, in traffic, you had to look carefully–you could see everything, it just looked a bit weird sometimes.

After reading all this Snake Skinner stuff, your inevitable question must be: will Chevrolet go to production with a Corvette like this? If the Dodge Viper falls on its face, though we may see some weight reduction; chances of a lightened-up, de-contented, high-horsepower car being built are nil.

If Viper proves to be a credible player in the high-sports market, we just might see a ZR1-SS, but a factory unit would have to address some of the criticisms discussed above. Right now, this is all speculation. There's been no official word and there probably won't be for a while. In the meantime, John Heinricy and the Corvette Group will sit back, watch Chrysler and test their nasty Snake Skinner.

After our evaluation, the the car returned to Detroit to begin a summer-long test regimen. Just before deadline for this article, a friend in the Corvette Group, Jim Ingle, called to discuss results of some testing he'd done. Now Jim, "Jingles" to those who know him well, is a Development Engineer who's specialty is test driving. On a drag strip, he is no doubt the fastest production Corvette driver. Using the acceleration strip at the Milford Proving Ground, which has better bite than does DPG's, and on a 60° day, he turned a 12.04 at 122.2 in the Snake Skinner. Damn! That's a majorly bad car!

Advantage: Chevrolet.


Vehicle specifications and test data

VIN: 1G1YZ21J0K5800081

Base price: $32.455
Price as tested: n/a
As tested includes: Standard equipment plus: ZR1 Special Performance Package ($31683) consisting of 5.7L dohc V8, 315/35ZR17 rear tires, 11x17 aluminum rear wheels, HD brake system, electronic air conditioning, special bodywork, selective ride and handling package, 6-way power leather adjustable sport seats, low tire pressure warning system, Delco-Bose sound system. The following items were then deleted: air conditioning, 6-way leather seats, low tire pressure warning system, Delco-Bose sound system.
Wheel base: 96.2 in.
Curb weight: 3130 lbs
Test Weight: 3305 lbs.
Engine: 5.727-liter, dohc V8, aluminum block and heads, port fuel injection.
Bore x stroke: 99.0 x 93.0 mm
Compression ratio: 11.0:1
Power: (s.1) 405hp@5800 rpm, est.
Torque: (s.1) 385ft/lbs.@4800 rpm, est.
(s.2) 425hp@6800 rpm, est. (s.2) 400ft/lbs.@5200 rpm, est.
Maximum engine speed: 7500 rpm.
Transmission: six- speed manual
Ratios: 2.68, 1.80, 1.31, 1.00, 0.75, 0.50
Rear axle ratio: 3.90:1 w. limited slip differential
Suspension ft/rr: control arms, transverse leaf spring, anti-roll bar, ride- adaptive shocks/control arms with lateral links, transverse leaf spring, antiroll bar, ride-adaptive shocks
Wheels ft/rr: Dymag cast magnesium 9.5x17"/Dymag cast magnesium 11x17".
Tires ft/rr: Goodyear 275/40ZR17, S-compound shaved/Goodyear 315/35ZR17, S-compound, shaved.
Steering: rack and pinion w. power assist
Steering ratio: 15.6:1
Turns, lock-to-lock: 2.25
Brakes: four-wheel disc w. power assist and ABS

Acceleration,
0-60: 3.87 sec.
1/4 mile: 12.04 sec. /122.2 mph
Lateral acceleration: 1.01g

Braking, 80-0 and 60-0 at impending lock-up: 228 ft. and 126 ft.
Slalom speed, 700 ft.: 65.8 mph.
Top speed: (w. s.1 engine) 185 mph, observed.
(w. s.2 engine) 190 mph, estimated.
MPG, EPA combination: n/a MPG, observed: n/a
Fuel capacity: 22 gal.

On August 5, 1992, the Snake Skinner ZR-1 was stolen in Canada. It was there for a GM of Canada promotional event at Mosport and was missing from the parking lot of the hotel where the GM employees driving the car were staying. It was recovered in Toronto by Regional Police the next day after a short pursuit. The driver’s door had been forced open and the steering column was extensively damaged, but otherwise, the SS was no worse for wear. Two teenaged suspects in the crime were arrested a short distance from where the car was recovered. Today, the Snake Skinner ZR-1 is on permanent loan by Chevrolet to the National Corvette Museum’s collection of ZR-1s.