Evolution of the Species
Thanks to the C6.Rs' brilliant performance in last year's ALMS series, this year's cars are largely carry-overs in the mechanical sense. Some rule changes have been enacted for the new season, however, forcing the Corvette Racing team to respond accordingly.
For 2007, ALMS regulations require that the gasoline used in competition be laced with 10 percent ethanol. The change required the GM Powertrain staff at Katech, under the direction of Roger Allen, to reach back into their computers and come up with an alternate mapping plan for the C6.R's engine-management system. According to GM engineers, if series officials decide to increase the ethanol content-to, say, 15 percent-an extensive (and costly) engine-hardware makeover will be required. Fortunately for the team, there appear to be no plans to proceed in that direction.
The other effect of the ethanol mandate is that power output has increased, as compared with the '06 fuel prescription. The tradeoff is an accompanying decrease in fuel mileage, an important factor in endurance racing. By spending untold hours in the computer lab prior to the season, GM engineers were able to achieve an operating envelope similar to that of last year's configuration, despite the fueling changes.
Another big factor in engine function and output this year is the use of a 5mm-larger air intake. The Automobile Club de l'Ouest (ACO), the sanctioning body for the European Le Mans series, is attempting to improve driver conditions by offering the larger intake size to teams running closed cars equipped with full (not suit- or helmet-contained) air-conditioning systems. The larger air-intake aperture should more than make up for any performance degradation caused by the additional weight of the A/C system and the increased load of powering an auxiliary system.
The C6.R's A/C system was designed by the GM HVAC group at Corvette Engineering, utilizing hardware virtually identical to that used in the third-row seating area of the Cadillac SRX sport-utility vehicle. The compressor and ducting systems are basically off-the-shelf parts from the GM parts bin. Fresh air is picked up from a filtered duct in the right-hand door, then sent through a finned condenser mounted in the tail of the car and into the passenger compartment.
The drivers receive cold air in several ways. There is a cabin outlet, just like in the SRX, mounted at shoulder height to the right of the driver. Air is also fed to the driver's helmet and to his back by additional ducting. All of these ducted outlets are augmented with their own fans, which force the air through the system. The system's compressor is mounted in the tail section and powered by the transaxle in tandem with the alternator.
As you might imagine, one of the potential problems with an A/C system is that the car's cabin essentially must be sealed in order to maximize the effect of the cool-air input. Because of this, a system failure is likely to be murderous on the drivers. After all, the only thing worse than driving in high-heat conditions is doing so in a closed up car with no flow-through air.
While the engineers are still working out the bugs that are inherent to any new system, the improvements in cabin comfort are already being felt and appreciated by the drivers. It's yet another way Corvette Racing is further refining the already formidable C6.R.