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."