Making your clutch selection is like trying on a suit. It's important to be sure the clutch system is going to fit the vehicle needs in terms of how the unit performs either at the track, on the street, or both.
The number one factor in determining clutch selection is load. The following are the three most important load factors.
VEHICLE WEIGHT - The mass or weight of the vehicle is an important factor in clutch selection. The flywheel weight has a great deal to do with creating enough inertia to get a vehicle rolling. Many older muscle cars are very heavy and have engines that produce higher torque numbers at lower engine speeds. This creates a high load situation on the clutch that can result in slippage if an inadequate clutch system is selected. The higher the vehicle weight, the higher the load on the clutch and the more clamp pressure is needed to move the vehicle.
ENGINE RPM OPERATING RANGE - The higher the operating RPM range of the engine, the more centrifugal clamp pressure is applied by the pressure plate. High torque low RPM applications will require higher clamp pressures, lower torque higher RPM applications will require lighter clamp pressures.
TRANSMISSION GEARING - Transmission gearing selection drastically effects the amount of clamp pressure required to move the vehicle, as well as the amount of centrifugal clamp pressure required to accelerate the vehicle through subsequent gear changes. By manipulating the transmission ratios, optimum gearing can be selected to match the load on the clutch system to maximize performance.
REAR END GEARING - High rear end gearing (lower numerically) puts heavier load on the clutch system. If you have ever tried to let out the clutch from a stop in second gear, you likely experienced difficulty getting the vehicle rolling without ‘bogging’ the engine. This same effect occurs when too high of rear gearing is used. This situation also requires the clutch to be slipped more on takeoff to make a smooth transition, resulting in accelerated wear to the clutch.
TIRE SELECTION - Tires with more traction or roll out, such as DOT or conventional slicks, allow the vehicle to hook up harder and are less likely to spin than street tires. When a tire spins, the load on the driveline is decreased, but when the tire is makes good traction, the load on the clutch is increased substantially and more clamp pressure is required in the pressure plate.
In addition to these load factors, there is ENGINE HORSEPOWER and POWER ADDERS. These factors are secondary; Increased horsepower will require additional clamp pressure. However, this is usually the result of a change in one or more of the load factors listed above.