Disc Diameter
The ubiquitous Tremec T56 is utilized in a variety of vehicles from the factory, but with varying clutch disc diameters depending on the application. So how does disc diameter affect clutch performance? According to Baty, LS1-powered Corvettes and Camaros come from the factory with an 11.5-inch clutch discs while Vipers are equipped with a 12.25-inch disc. "The Viper's clutch is only 3/4 inch larger, but in the clutch world that's huge," says Baty. "To give you an example, the effect is similar to using a larger breaker bar to loosen the lug nuts on your wheels. It's what we refer to as the 'arm' of the clutch, and the farther outward you get the friction material, the greater the holding capacity. In other words, if you compare an 11-inch clutch with a 12-inch clutch that has the same clamp load and point of friction, the 12-inch clutch will hold more torque hands-down every time."
Twin-Discs
When a traditional single-disc clutch system can no longer hold an engine's torque, multi- or twin-disc clutches are required. By utilizing a floater assembly and two discs, they double the surface area available to transfer torque to the transmission. The result is significantly enhanced grip for a given clamp load. There are, however, some caveats to keep in mind. "Since you now have two discs and a floater that require the same release rate as a single disc, the release ratios need to be fast, and the drawback is that they tend to work like an on/off switch," Baty says. "A single-disc unit certainly has a limit to how much torque it can hold, but we have customers using our 11-inch DFX assembly in cars that produce over 900 lb-ft of torque at the wheels without any problems."
Company Evolution
"Centerforce was conceived in the early '80s when Bill Hays, who also founded Hays Clutches in the '50s, began brainstorming new clutch technologies. With the desire to engineer a solution to the 'sticking over-center' problem of diaphragm-style clutches, Bill designed and patented the Centerforce weighted clutch system. This design increased pressure plate clamping force while maintaining easy pedal effort and eliminated the diaphragm's tendency to 'stick over-center'. Later in the decade, he invented, designed, and patented the Centerforce Dual Friction clutch system, which was awarded Best New Performance Street Product by SEMA. A member of SEMA since 1977, Centerforce has been nominated for the PWA Manufacturer of the Year award many times, winning it in 1998. Bill was also inducted into the SEMA Hall of Fame that year for his work in the performance aftermarket industry. Over the decades, Centerforce outgrew its two original California-based manufacturing facilities and in 1994 relocated to a new, 47,000-square-foot shop in Arizona. New patents have since followed as well as continuous improvements to product offerings. Today Centerforce has over 1,700 clutch applications available, and plans are being reviewed to nearly double the size of our facility to keep up with the demands of the performance automotive world. To this day, Centerforce is still a three-generation family-owned business."
Puck-Style Discs
While OE clutches typically use full-faced designs for smooth engagement, high-performance aftermarket discs often employ a multipuck arrangement to increase clutch bite. On a traditional disc, the force exerted by the pressure plate is evenly dispersed throughout the facing. A puck-style disc, on the other hand, concentrates the pressure over a much smaller surface, thus increasing the force exerted on the flywheel. "Imagine a bare-footed 100-pound woman standing on your back giving you a massage who suddenly puts on high heels," Baty quips. "It's going to hurt a whole lot more with the heels. This is essentially the same concept puck-style discs employ."
Weight And Traction
Horsepower isn't the only thing to consider when selecting a clutch. For a given power output, as vehicle weight and traction increases, so do the loads on the clutch. "Heavier vehicles tend to require more clutch slip when taking off from a standstill, and this has an adverse effect on the life of the clutch," says Baty. "When you slip the clutch, it generates lots of heat, which is the number-one killer of a clutch. Increasing mechanical advantage through gear reduction can take some stress off the clutch and driveline, which is why five- and six-speed transmissions with low First gears are becoming so popular. Traction can tremendously impact clutch loads, which is why drag cars are the most demanding of all applications."