The Corvette Racing crew had a challenge: make sure that one of the most technically advanced sports cars ever developed by General Motors could flat-out race on ethanol fuel. Developed to compete in ALMS races on E85 racing fuel, GM's LS7.R engines were modified from the E10 specifications of the 2007 race season.
"Fuel system O-rings were specified to be compatible with E85," noted Roger Allen, Engine Program Manager for the C6.R (Corvette 6th generation, Racing) program. "The fuel injectors and fuel pump were specified to handle the additional fuel flow requirements. Ignition spark advance was optimized for E85, and the fuel calibration was optimized."
Through 2007, Chevrolet's factory team won 63 races, seven consecutive ALMS GT1 manufacturers and team championships, and six straight drivers championships. Corvette Racing also has had five class victories in the 24 Hours of Le Mans since 2001. The 2008 race season marked Corvette's 52nd year in international road racing.
The C6.R program continues the tradition of racing production-based vehicles. "The lessons we're learning in how to continue to develop the horsepower while improving fuel economy and making sure all of the parts are durable—that's something that we're talking to the powertrain engineers about every day," said Steve Wesoloski, Road Racing Group Manager for GM Racing.
Although the advanced engineering group is kept in the loop on the lessons learned from LS7.R development work—such as optimizing wide-open-throttle performance with E85 fuel—not every technical tweak is directly applicable to today's production applications. "Their focus on emissions, idle quality, and part-throttle fuel economy is much more critical, (so) a direct transfer of our hardware or calibration is not logical," noted Allen.
The practical approach heavily influences Corvette Racing's engineering decisions. "While specific E85 engine tuning—i.e., compression ratio, camshaft, inlet lengths—would certainly be something to look at in a highly competitive environment, it was not considered necessary in terms of the additional budget requirements for our (ALMS) GT1 program," Allen said.
Running the 7.0-L Small Block V8 engines on E85 racing fuel proved to be a relatively easy technical feat. "The transition from E10 to E85 was seamless and uneventful," noted Allen. "If I had to say what area we had to work on the most, it would have to be fuel economy. With the reduced energy content of E85, much work was done to be as efficient as possible. Calibrating the fuel control to maximize the air/fuel ratio and optimizing areas like deceleration fuel cutoff became important enablers to reduce consumption."