The 2015 Corvette Z06 and Corvette C7.R were developed alongside each other and thus, have many things in common. One area where the racecar differs from the street car, though, is under the hood. The C7.R actually produces less power than the 650 horsepower supercharged Z06, and Chevrolet’s Senior Manager of Performance and Racing Engines, Russ O’Blenes, recently explained why that is.
The TUDOR United Sportscar Championship series in which the C7.R competes mandates that all cars must not have an engine larger than 5.5-liters for competitive reasons. This forced the Corvette Racing team to forego the supercharged LT4 engine in favor of the naturally aspirated 5.5-liter Pratt & Miller unit.
“The TUDOR rules are developed to allow for parity between many vehicles and engine packages. They use engine displacement and restrictors to manage this,” explained O’Blenes. “The supercharged 6.2L LT4 in the Z06 makes well over 100hp more than we currently compete with in the GTLM cars.”
Despite the difference, the Corvette Racing team is still able to learn from the 5.5-liter engine and relay any information they may have gained to the production Corvette team. This is because the two engines share technologies such as their direct fuel injection systems.
“Even after development finished, we still work closely with the production team to share lessons learned and discuss engine and development techniques that help the production and racing engines improve,” O’Blenes said.
The Corvette Racing team is constantly making fine adjustments to the 5.5-liter engine in order to gain small amounts of power, however due to rule restrictions, they are only able to squeeze so much power from the engine without breaking certain regulations.
“We do not find 5hp gains, it just is not there. Instead, we are looking for 0.5hp gains, but if we find 10 of them then we’ve gained the 5hp that we hoped for,” O’Blenes said.
“That is why the details are so important. From how the engines are built, to how the data is collected. It is very difficult to consistently measure half a horsepower. Everything in the test cell must be monitored and controlled to be able to trust the data,” he added.
Corvette Racing engineers can’t just keep adding horsepower without thinking of the other aspects of racing, though. Having lots of power on tap is great, but they also need the reliability to tackle 24-hour endurance races while maintaining good fuel economy
“It is all about the details,” said O’Blenes. “Every component in the engine must be perfect and the right part. We have developed this engine for many years and continue to push each component to get the best performance and reliability possible. It is important to break parts from time to time on durability to ensure that you are not leaving anything on the table. Too heavy of a rod or too much valve spring pressure for example, you need to be near the edge but not fall off.”
The Corvette Racing team will fire up their 5.5-liter engines for the next leg of the TUDOR United Sportscar Champinship, the Tequila Patron Sportscar Showcase at the Streets of Long Beach on April 18.