Though the CTS-V has a 100hp advantage over the GXP.R, Steve contends the 3,100-lb sedan is no match for the 2,808-lb tube chassis coupe. Thankfully, the Cadillac has only Porsches and detuned Corvettes to compete with in the SCCA SPEED World Challenge. The Brembo brakes are kept in the tradition of the production car, but utilize heavier-duty race calipers and 355mm front and 325mm rear rotors for decreased brake fade. Don't mistake the chassis for stock, either, as in addition to the rollcage and carbon fiber body panels, the CTS-V sports a Corvette-style double-wishbone suspension with fabricated control arms, beefy sway bars, and coilovers. The modified rear cradle, aluminum radiator, Fuel Safe 22-gallon fuel cell, and the lower/rearward orientation of the motor also separate the race car and production car. OZ Racing one-piece forged 18x11 front and 18x12-inch wheels are housed in the extended wheelwells, and use spec Toyo Proxes RA-1 275/35R18 and 335/30R18 tires to make the long wheelbase sedan "feel like a go-cart," according to driver Andy Pilgrim.
In comparison, the 2,435-lb ALMS C6.R really is a go-cart, especially with 640 lb-ft of torque. The slender poundage is attributed to the use of a completely carbon fiber body, polycarbonate windows, ATL 90L fuel tank, stripped interior and amenities, and a very efficient truss structure. Believe it or not, the C6.R uses the base Corvette's hydroformed steel chassis (to which the rollcage is welded)-and not the Z06's aluminum frame-for strength and welding compatibility. A substantial set of carbon disc AP Racing four-piston brakes halt the Vette at an alarming rate while also working in concert with super-strong one-piece forged magnesium BBS 18x12.5 and 18x13 wheels to keep unsprung weight to a minimum. The short and long arm (SLA) suspension (based off the stock Corvette setup), which the other two race cars were modeled after, employs fabricated chrome-moly upper and lower control arms, a machined aluminum knuckle, adjustable coilover shocks from Penske with remote reservoirs, and carbon fiber sway bars. A close partnership with Michelin has enabled extremely consistent and predictable grip with various sets of 290/33R18 and 310/41R18 slicks.
Perhaps the Corvette's greatest advantage, at least over the other two race cars, is its aerodynamics. Though it also uses a flat bottom (like the other two), it has a much more substantial front splitter and undertray to reduce front-end lift, plus a rear diffuser to reduce turbulence behind the car. Depending on the adjustments to the wing, the C6.R generates anywhere from 700 to 900 lbs of downforce at speed, which is enough to enable almost 2Gs of lateral acceleration. The trademark heat extractor hood is also used to reduce lift from the high-pressure area created from the air passing through the grill and aluminum radiator. No fans are used with the radiator, as it actually creates a restriction. Meanwhile, the air intake for the motor, as well as the oil cooler and brake ducts, take full advantage of this airflow. Underbody and side airflow is scooped up by the rear brake ducts and coolers for the transmission and differential, which in conjunction with Mobil 1 high-temperature lubricants, is how the C6.Rs not only manage to survive 24 hours of driving at 10/10ths-but also how they manage to win. Surprisingly, this doesn't deviate too far from the Z06, which certainly makes the street car's heritage apparent. This has to make you wonder how many other race-inspired designs will trickle their way into production cars.