With the possible exception of the hunnish Dodge Viper, the C6 Corvette is unique among domestic vehicles in its ability to make just about any driver feel like a multiple ALMS champion. Amply girded with deep reservoirs of power, a denture-dislodging set of brakes, and a painstakingly refined suspension system-all operating under the benevolent aegis of a sophisticated computerized safety net-the latest iteration of Chevy's long-running sports car offers a peerless platform for pushing one's driving abilities to the limit with minimal risk to life, property, and reputation.
But for all its baked-in puissance in most operating environments, the C6-especially in base form-is not without room for improvement as a sometime track car. These inherent deficiencies came into sharp focus during one of our recent track sessions at Gainesville Raceway, when a colleague at another magazine decided to put his '05 Z51 coupe through its paces on the facility's 1.6-mile road course. Perhaps the most significant problem lay in the car's habit of spinning its inside wheel when accelerating out of turns, a tendency amplified by the aging all-season Michelins installed by the previous owner. And while the factory Z51 binders performed admirably up to a point, repeat lapping revealed a not-inconsiderable propensity for brake fade, resulting in a few hair-raising moments and at least one sod-scattering detour through the infield.
Much as we enjoyed witnessing some of these antics, professional responsibility ultimately prevailed, and we resolved to address the car's shortcomings with a few carefully selected aftermarket upgrades. We began by contacting OS Giken, a leading manufacturer of limited-slip differentials for foreign and domestic performance vehicles. Giken's Sean Fenstermacher recommended the company's OS Super Lock LSD unit, which is a direct replacement for the stock diff in C6, Z06, and ZR1 models. (The company also offers versions for the C4 and C5.)
According to Fenstermacher, the Super Lock's chief advantages lie in its unique construction. "The Super Lock is a clutch-type unit equipped with 28 steel clutch plates with very minimal preload. This provides a smooth lockup [all the way] to full lock. It also eliminates wheelspin, while maintaining smooth, almost open-diff-like corner entry. This results in faster exit speeds for our track and autocross customers."
Our '05 Z51 coupe had a habit of spinning its inside wheel when accelerating out of corner
Though not specifically designed for drag racing, the Super Lock is also said to pay dividends at the strip. "For drag customers, our diff provides a smooth and progressive lockup to both wheels equally, enabling increased stability during hard launches," says Fenstermacher.
Durability is also improved over stock, thanks to the inclusion of hardened stub axles, a forged case and pinion gears, and the use of heat-treated components throughout the unit. No break-in period is required, and fluid-change intervals are unchanged over the factory recommendations. (You'll need to use OS Giken's proprietary fluid, however.)
For serious racers, the Super Lock's preload, lock timing, and ramp angle are fully tunable, making it possible to tailor the unit's responses to best suit different suspension calibrations and track layouts. The configuration works so well, in fact, that track star Danny Popp is currently running a Super Lock diff in his NASA C6 race car.