How much horsepower can a stock clutch hold?

Technically, clutches don't transfer power, they transfer torque. According to Dirk Starksen of Advanced Clutch Technology (ACT), the formula is T=NxRxFxP, where:

• N=number of clutch surfaces
• T=torque capacity (foot-pounds)
• R=radius of gyration, or size (feet)
• F=coefficient of friction
• P=pressure plate pressure (pounds)

For stock clutches, N is 2, F is about 0.25, and P is 1500-1650 lbs, yielding a maximum hold of about 250 ft-lbs of torque.