The Turbo GT
by Mike Guyette

In 1976, a prototype "turbocharged" (it wasn't) fastback coupe was built to showcase even more radical aerodynamics. By 1978, the Greenwoods chose a blow-through design versus a draw-through approach to turbocharging because of its superior performance, despite the intracasies involved in making this fledgling technology work consistently and reliably. While the rest of the Corvette world was playing with the simpler of the two turbo systems, the Greenwoods decided the inherent performance gains of the fully pressurized arrangement warranted further development.

The 1976 Turbo prototype featured more smoothly integrated fenders than the Sebring GT and the short vertical rear spoiler of the GT gave way to an integrated wing. The notchback design of the last Stingray was filled in and became a “fastback” with a large rear, non-opening glass window. The prototype was painted a two-tone silver-over-gray, as was their #77 “Batmobile” racer -a color scheme that would debut on the ’78 Silver Anniversary model (along with a large glass backlight). Taller sport style mirrors were prototyped (but didn't make it to production) in order to aid in over-the-fender rear vision, a shortcoming of sport-mirrored Sharks.

Sidebar by Norm Bogiel

The "turbo" cars were started shortly after the GTs. I remember seeing some skinny guy walking around the shop every once in a while. I asked one of the other guys in the shop who that was and he said, "That's your real father". I asked him what he meant and he told me that it was Zora Arkus Duntov. He and John were consulting on the turbo car. I guess his shop must have had something going inside GM and they were using (helping) John to see if it would work and what reaction would be. I guess I should mention another name that kept cropping-up too. All of the street cars (and most of the prototypes) were built on brand new Corvettes. As I recall they all came out of Mancuso Chevrolet in Chicago, IL. People who have followed John's work with the street cars will be familiar with the fact that Mancuso was into a lot of these deals. And he raced some of the Greenwood cars, too.

The first one we built as a prototype wasn't really a turbo at all. It was a stock automatic that we did the mock-up body work. We didn't have much idea of where the car would go so we just filled the gas tank and then I started working on the rear glass area. I filled-in the rear deck with styrofoam and mocked-up the new rear glass design. Then we simulated a turbo bubble on the hood, did the turbo-style fender cut-outs and glass everything. We painted it red and silver and sent it out on the show circuit with a van called "Future Shock". The car wasn't really intended to be driven around much but, by about half way through the show circuit, in the middle of winter in Kansas City, it ran out of gas. They couldn't figure out how to refill it so we had to send out one of the kids from the shop with an electric fuel pump and a gas can. When we got the phone call, he didn't get to go home or anything. John just put him on a plane and sent him out to fill up the car. I thought that was pretty funny.

Another thing that happened with the turbo mock-up was that BFG picked it up for part of the tour and used it in magazines as part of their Radial T/A promotion. We got a lot of orders and inquiries from that ad. Enough orders that the car should have sold more! But marketing a car and actually getting up an organization to deliver can be two very different things.

The Turbo prototype was well received by the motoring press, but Sebring GT production became more of a priority. Cash flow dictated that all efforts be directed toward finishing the cars already ordered, so R&D of the Turbo program was back-burnered for more than a year while the GTs were finished. After tooling parameters were established, the lone Turbo prototype was rebodied as a Sebring GT and sold.

Refinements were made to the orginal Turbo design and in 1978 three production models were built. A few styling changes were necessary; the most significant due to the new glass back of the 25th Anniversary edition. The fastback design was no longer an issue, so the rear wing was made wider to flush-fit the extended fenders. It was also made thicker with an upturned trailing edge to better manage the airflow off the new rear window. Fenders were unchanged from the prototype, featuring five vertical slots at the rear of the front fenders which matched those on the new Turbo hood. A single NACA duct on the right side of the hood allowed additional cooling to the warmer-than-usual engine compartment.

Although the engine of choice was the L-48 model due to the lower compression ratio, Turbo GT #1 has the L-82 engine option. The additional boost pressure could cause premature detonation, and the 8.5:1 compression ratio of the stock L-48 engine didn’t totally resolve all problems relating to the 7 psi of boost. A water injection system was devised to help alleviate potential self-destruction. Fed from the windshield washer reservoir, this primitive charge cooling setup could be considered the precursor to today’s intercoolers.

Other pieces and systems were custom made to overcome the problems associated with the blow-through setup. A right side exhaust manifold was cast to hold the Air Research T04 turbo and wastegate; a cross-over exhaust pipe connected the right manifold to the left; and a custom bent pipe connected the turbo to the stock exhaust. A cast aluminum bonnet fed by the turbo sat sealed atop a Holley 650cfm carburetor, specially prepared to handle the pressure. To insure adequate fuel delivery, two electric pumps took over the duties of the original mechanical unit. The TH350 transmission was tweaked to handle the extra power that would be generated.

The suspension didn’t go unnoticed as this was John Greenwood’s forté. Rear Koni coilover shocks and heavy duty sway bars were a given, while the rear suspension utilized a unique upper and lower A-arm configuration, not unlike that of the 1997 Corvette. This “radical” configuration virtually eliminated the dive and squat associated with hard braking and acceleration. The physical location of these suspension pieces necessitated the formation of a fiberglass interior rear floor. The rest of the interior remained stock except for the boost guage neatly integrated into the dash. The serial plaque on the ashtray door indicated which of the three Turbo GTs you were riding in.

The first two built were black with red interior, the third, burgundy with saffron interior. I purchased serial number 1002-78 in 1991 from the original purchasing dealer. Since then a friend, Lou Pittack, and myself found #1001-78 at Corvettes @ Carlisle 2000. Lou purchased the car from the second owner. As it turns out, the first owner of Turbo GT #1 was also the owner of Daytona #2, which Lou also owns! After spending many years apart, both of these cars became reunited again! Turbo GT #3 had been "missing" for many years, but just recently turned up (Nov. '04). Car collector Roger Abshire, who also owns a widebody Greenwood-style race car purchased the elusive #1003-78 from a gentleman in New York, where the car has been since new. The car was in shoddy form, and several changes had been made to it over the years, including ACI "Duntov" style rectangular headlights, aftermarket gauges, an opening hatch and later model seats. Fortunately, Turbo #3 still has its original turbo setup. Roger plans on restoring this car to its original specifications, although he plans on retaining the headlights and opening hatch.

Like the Sebring GTs, the Turbo GTs had similar badging and serial plaques, although the Turbos’ plaques proclaimed the forced induction with the word “Turbo” on it. Because all three Turbo GTs were built as 1978 cars, the plaques indicated such with serial numbers stamped as “1xxx-78” , where the “xxx” refers to the serial number. The Greenwood GT wheel discs were intended for the same American Racing Vector wheels as used in the Sebring GT, however, no pictures to this date indicate that they ever made it on the Turbos.

Logos consisted of the word “Turbo” above the vents on the front fenders and also underneath the rear wing. The circular Greenwood logo discs adorned the B-pillar as they did on the Sebring GT. On the dash was a neatly integrated boost gauge, and two small lights were incorporated into the speedometer face. These lights indicated when the water injection system was low on fluid, and when it was actually being utilized.

Besides the unique blow-through turbo installation, all Turbo GTs had unique upper/lower A-arm and coil-over suspensions in the rear. This setup required “massaging” of the floor panels where the battery and storage bins were located. Because of the custom rear suspension used in the Turbo GTs, the stock parking brake cable and brake hoses were replaced with longer units. American Custom Industries continued to make several virtually identical cars after the departure of the Greenwoods in 1979, and were renamed the American Turbo. At least one of these had the blow-through turbochager setup and special rear suspension. As a selling point at that time, a few American Turbos were sold as Greenwood Turbo GTs, complete with leftover serial plaques but with incorrect serial numbers. Although virtually identical to the Greenwood version, these cars are considered replicas. I have seen pictures of a couple of these cars including a Turbo Sportwagon and a big block-equipped Turbo body style. No cars would be built in 1979 by the Greenwoods, but 1980 saw the beginning of develpoment of their next race/street car, the Daytona.