The new C6.R is based on the Corvette ZR1 production car, and, as seen in the photo here, the latest racer bears much more in common with the road car than did the dominating GT1 machine it replaces. As for the GT1 class, the ALMS will phase it out in favor of a unified GT2 beginning in 2010.

For the remainder of 2009, the cars are powered by a 6.0-liter small-block V8 based on the 7.0-liter LS7.R found in the GT1 version. To reduce displacement, engineers shortened the stroke from 3.875 inches to 3.320 inches. Also, air-intake restrictor diameter decreases from 30.6 millimeters to 28.6 millimeters. Horsepower drops from 590 hp to 470 hp, while torque decreases from 640 lb-ft to 535 lb-ft, according to Corvette Racing.

To comply fully with GT2 rules next year—sporting authorities granted the team an exception allowing the 6.0-liter engine for this season's five races—the team will use a 5.5-liter production-based small-block V8. Horsepower and torque are yet to be determined. Both engines continue to be powered by E85R ethanol racing fuel.

Other highlights mandated by GT2 rules include:

-- ZR1 body design, aerodynamic package,

aluminum frame and chassis structure, steering system and windshield.

-- ZR1 hydroformed aluminum frame featuring

a fully integrated tubular steel safety cage; GT1 C6.R used a steel frame.

-- Production-based ZR1 fenders and wheel flares; GT1 featured wide, louvered custom fenders.

-- Rear-wing width reduced 25 percent; flat-panel rear diffuser without fences or strakes; front splitter extends only as far as the ZR1's.

-- Steel brake rotors replace carbon discs; wheels are now made from aluminum rather than magnesium.

-- Overall weight increases from 2,580 pounds to 2,745 pounds.

-- Wheelbase (105.7 inches) remains unchanged; overall length decreases by 2.5 inches because of a splitter change; overall width decreases by 0.1 inch as a result of a fender change.