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Turbocharged Corvette Prototypes - Early Aspirations

Think the '87 B2K was the first turbocharged Corvette?

Wayne Ellwood Mar 30, 2007

The Phase I Turbo Corvette featured a louvered hood and a Randy Wittine-designed pinstripe package.

In automotive engineering, as in life, there are few absolute and enduring truths. What seems impossible today may become practical in 10 years. And, 10 years from now, what once seemed like a revolutionary idea may prove to have been just another outlandish folly. Is this the story of the turbocharger?

A Swiss engineer named Alfred Buchi invented turbochargers in 1905. Development was accelerated by military imperative, especially during World War II. Hot-rodders experimented with turbocharging after the war, but it was not until the early '60s that significant automotive applications were tested. Both the '62 Oldsmobile F-85 "Jetfire" and the Corvair Monza/Monza Spyder were fitted with turbos. The Olds was the first to break the one-horsepower-per-cubic-inch standard.

Corvettes have historically made poor candidates for turbocharging. The restricted space of the car's engine compartment means that installing the extra plumbing is more difficult. Additionally, the cost of the special exhaust manifolds (to place the turbocharger near the exhaust source) and extra-large pipes (to evacuate the exhaust after it has been used) simply cannot be justified without a significant power increase. There are also implications for service life and maintenance expense. Finally, underhood heat is a critical factor.

Back in the '70s, when the Corvette group began its in-house research into turbo applications, it contemplated the use of a smaller engine-possibly a V-6-to generate V-8 levels of performance. But this idea was not popular with the Corvette community. So, while other GM groups worked on smaller engines, Corvette engineers stuck with the basic 350 as their preferred platform.

By 1976, Jim Ingles had developed several turbocharged 350s (see sidebar by Gib Hufstader). Then, in 1978, Vince Piggins' Product Promotions group took this early engineering work and began testing the concept for production. Piggins' group reasoned that a turbo car would be fast enough to breathe new life into the aging C3 design. Turbos offered more power at little or no cost to fuel economy, and in milder states of tune, the whole system could be made virtually transparent to the user.

The first "Piggins" car would become known as the Phase I Turbo. Photographs of the car, based on a silver '79 L48 Corvette, began appearing in magazines at around the time of that year's new-model introductions. Shortly afterwards, a second turbo car-sporting new red and black pinstriping penned by Randy Wittine-began appearing at major auto shows and race events. Engineering for both cars was conducted under the leadership of John Pierce. (Interestingly, the Phase I car also prefaced the idea of a functioning hatchback, using a Cars and Concepts kit.)

The Phase I turbo system had three basic components. First, a Bendix EFI "batch injection" package was adapted from Cadillac. This system would trigger four injectors on one pulse from the distributor, then trigger the other four on the next rotation. A Garrett AiResearch T3 turbocharger was also fitted. The key to effective engine management was a prototype Delco closed-loop knock sensor and control system, which provided information on ignition within the cylinder. All components were coordinated by an electronic "brain," which also monitored engine rpm, manifold pressure, engine and air temperature, and the readings of a closed-loop oxygen sensor.

The results were encouraging, if not extraordinary. Quarter-mile runs came in at 14.38 seconds at 95.64 mph using 6.5 pounds of boost.

Introduced in late 1979, the Phase II car utilized an L82 engine fitted with an L48 camshaft, which had less overlap on the intake and exhaust sides. An AiResearch T3 turbo, set at 7 psi and fitted with an integral wastegate, was again utilized. This system fed the engine through a new throttle-body-injection system from GM's Rochester Products division. Upgraded Delco electronics monitored the interaction of the package's components, and a knock sensor allowed for ignition retard when detonation was sensed.


The last of the turbo C3 prototypes, the Phase III, featured aluminum heads and other performance-enhancing features.

A notable innovation was the method used to reduce turbo lag. In contrast to a blow-through (carbureted) system, the TBI engine's throttle blade, which controlled incoming air, was upstream of the turbo. This meant that when the throttle was shut off, the turbo effectively ran in a vacuum, creating a backlog of pressure. When the throttle was again opened, the vacuum created a ram effect, speeding up response time.

All other mechanicals were stock Corvette, including the Turbo 350 transmission and 3.55 axle ratio with Posi-traction. The suspension was Chevrolet's FE7 Gymkhana option, and the tires were 255/15s mounted on 8.5-inch rims.

An updated look accompanied the new car. The base body color was rich metallic silver and was embellished with a striping scheme combining claret (reddish maroon), deep red, and flaming orange. A similar color scheme adorned the seats and door panels.

The last of the turbocharged C3 prototypes, the white-and-blue Phase III Turbo car was unquestionably the most advanced and sophisticated of the series. Piggins' group had continued to refine the existing turbo design, adding aluminum heads and other trick parts to pare weight and enhance performance. But the package's high cost, combined with tightening federal emissions regulations and advances in naturally aspirated engine technology, spelled doom for the project.

Obviously, these cars were not the last of the artificially aspirated Corvettes. Turbo work was reactivated with the C4 and the Callaway-produced RPO B2K. But there was to be one more twist for the turbo C3s.

At the time, the National Council of Corvette Clubs (NCCC) was deeply involved in fund-raising initiatives in support of the Spina Bifida and Hydrocephalus Association. From 1980 through 1982, the council contracted some very accurate replicas of GM's Phase II, Phase III, and '82 Collector Edition cars for the annual raffle.

The 1980 raffle featured the Phase II car. John Gibson, of Corvette News, provided the contacts at Piggins' group, and NCCC president Tom Henry challenged his many organizers to finance the deal. By the time the whole package was approved, it included not just the car, but matched Mid America Designs apparel and a full set of leather luggage as well.

The job of preparing the car was contracted to several partners. Cars & Concepts, in Brighton, Michigan, installed the gas-strut hatch system. The car was then sent to American Custom Industries, in Sylvania, Ohio, for paint, interior, and turbo installation.

The replica car was different from the original Phase II in a few important ways. Instead of the prototype's developmental engine, the replica featured a regular L48 fitted with an off-the-shelf Martin turbocharger kit. This system provided a reasonable power increase and was easy to maintain.

In addition to the extensive leather work performed on its interior, the replica's console-mounted instruments were swapped out for a set of Javelina Digitron II digital gauges. By the time the whole car had been assembled, it made for quite an attractive package. The Phase III replica, which was raffled in 1981, was not quite as sophisticated but followed essentially the same pattern.

As suggested at the start of the story, few viable technologies ever really disappear. Turbocharging work continued with the C4, as customers clamored for more power to keep pace with the Vette's international competition. Corvette chief Dave McLellan continued developmental work on the turbocharger option even as the ZR-1 was being developed. This work led to the Callaway-designed RPO B2K package.

Separately, the IMSA GTP race car, based on a Lola chassis, was being used as a live test bed for both the turbocharger and a pair of newer-generation engine-management systems. Many of the lessons learned here were applied to the twin-turbo LT5 developed for the 1990 CERV III engineering concept.


Dave Mclellan On C3 Turbo Development
"Supercharged Corvettes were being developed even before my time. The technical issues always centered on package space, heat, fuel control, ignition timing, and octane demand versus detonation. [This was a] virtually insurmountable set of obstacles in those days of analog control systems.

"John Pierce, working in Vince Piggins' Product Performance Group, did a carbureted turbo Corvette. Jim Ingles tested this and all subsequent generations of turbo Corvettes. [Magazine-listed] horsepower numbers for these cars are at best unreliable. But . . . Jim's acceleration times don't lie and can be trusted as an accurate indication of how these cars were actually performing.

"Having to pressurize the four-barrel carburetor was our worst nightmare with these early turbo cars. A backfire through a pressurized manifold full of fuel could literally blow the lid off the engine. The lack of sophisticated fuel and spark management forced us to control detonation with not much more than a very rich fuel mixture and 103-octane fuel. We could gas up only at the GM Research pump. This drastically limited the range of the car and made it useless for touring. These cars were, however, great fun to drive while the fuel lasted and the engine held together.

"These were definitely not cars that could be turned loose in the hands of a customer. Nor did we have any hope of selling them as emission-certified automobiles. Later in the C4 program, we continued with the development of turbochargers as one option, but by that time we had developed much more sophisticated electronic emissions controls."


Gib Hufstader On C4 Turbo Development
"Developments for the new C4 took place against the same regulatory background of restraint. But we did have some significant achievements. For example, I worked on the stainless-steel tubular headers for the California engine to help meet the emissions requirements. I also worked on the throttle body for the L98 package with Fred Langenstein, and then we moved on to develop the first LT1 aluminum heads.

"One special project we developed was the 1983 to '85 C4 twin-turbo program. You will recall that Callaway eventually delivered a turbo car. But during the developmental stages, we also did some work on this concept. Our car was developed using Creative Services, in Troy, Michigan. My job was to work on the packaging for this engine.

"I should also step back for just a second. I had built another turbo for Jim Ingles back around 1976. It was a Switzer unit, right-hand mounted, up high. It blew into the carburetor, which was a source of complication. You had to seal all the shafts and linkages; otherwise, you just blow gasoline out. It was also a manual transmission, which isn't the best configuration. Still, it worked quite well, and when you stood on the gas, you would lay rubber for 80 feet or so. Jim burned that car to the ground . . . literally.

"The 1985 turbo C4 project was a bit of a learning experience for us too. We had started by using small Warner-Ishi [Borg Warner-supported] units. But . . . Mitsubishi wanted into the program very badly and had leveraged our purchasing group. So we switched to the Mitsubishi product, which was larger. Still, we designed the intake, intercoolers, fresh-air intakes, and turbo placement. Then we set about doing all the drawings for parts release.

"Callaway's design differed from ours in several respects. We had placed the turbos up high, to assist in oil drainage, which was the opposite of Callaway's design. Of course, the lower placement had more space, and wherever you place a turbo, you do concentrate heat. There were tradeoffs in each layout."



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