Chapter 7

Clutch Tuning

Clutch tuning is managing the clutch system to obtain the desired performance.  In drag racing, this is achieving maximum vehicle acceleration with little regard to clutch system wear.  Clutch tuning in a street application may be obtaining maximum service life.

TUNING A CLUTCH FOR A GIVEN APPLICATION

A Long Style assembly may be tuned through two adjustments – spring and centrifugal pressure. 

Centrifugal pressure is not a linear function and increases substantially at higher engine RPM.  A vehicle that requires the clutch to be disengaged to shift will be limited in the amount of centrifugal clamp pressure that can be utilized.  Linkage components will encounter higher stresses as the centrifugal clamp pressure is increased, making disengaging the clutch more difficult.

Applications using clutchless transmissions have no limitations on centrifugal clamp pressure.  Use of centrifugal clamp pressure allows the use of less initial clamp pressure at low engine RPM, allowing the vehicle to achieve maximum traction and acceleration leaving the starting line.  As the vehicle accelerates and the engine RPM increases, the centrifugal pressure increases and will allow the clutch to generate sufficient clamp pressure to handle the load of successive gear changes.

The friction material used on the clutch disc will effect how much clamp pressure is required to hold the vehicle.  Friction materials with higher coefficients of friction require less clamp pressure.  Other factors to consider are wear and engagement characteristics.  

By increasing the number of clutch discs in the assembly, the clamp pressure needed will decrease, the clutch will engage smoother, clutch diameters can be decreased, and overall service life will increase.  Reducing the diameter of the clutch will also allow the engine to accelerate and decelerate quicker.  This is the principle behind using small diameter clutches in oval track racing. 

Street/strip vehicles can benefit from the ability to adjust the clamp pressure for maximum performance at the race track.  We would advise a customer to use an adjustable pressure plate that has a range capable of accommodating both street and strip use.  For street driving, we would recommend the clutch be adjusted to maximum pressure to accommodate the lower RPM and higher torque load.  At the race track, the pressure may be reduced to allow maximum acceleration with minimal tire spin, and also because the clutch is operating at higher RPM and more centrifugal clamp pressure is applied.

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