Turbocharged Corvette Prototypes - Early Aspirations

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.