By Mike Bumbeck
Photos by Mike Bumbeck and
RPS Performance Products
9/29/05

eat is the sworn enemy of the clutch out on the 1320. Friction created by the engagement of the clutch disc material to the flywheel friction surface and pressure plate releases heat as it transitions the energy of the engine into ground pounding power. Too much power for the clutch setup, and the clutch will start to slip and create more heat. More heat will cause the clutch disk material to lose efficiency and slip more – creating even more heat.

Excessive heat can burn up the clutch and put everything back on the trailer or on the tow hitch. Even worse, things can get dangerous. Some early AA Fuel Dragster "slipper" clutches created so much heat that they turned into white-hot circular shrapnel, shearing the cars in half. Just ask "Big Daddy" Don Garlits, who cooked up the design for his rear engine dragster while in the hospital recovering from a fiery clutch explosion that destroyed his dragster and nearly destroyed him.

While clutch technology as it applies to drag racing has come a long way, heat is still the enemy, and can bring a world of frustration to the table whether you're rowing through the gears on a bracket car or trying to figure out how to get thousands of nitromethane induced horsepower down to the ground without you or your clutch setup getting burned. Finding the right combination of friction materials and clamping force for consistent launches that won't turn the transmission into an expensive rock tumbler is the goal.

A factory Mustang flywheel shows the difference in material hardness. Variances in can remain even after the surface is machined flat, causing corresponding difference in grip. This degree of overheating can also result in flywheel shatter.

SUPER FLY

Drag racing puts some heavy-duty demands on every component of the clutch, but the flywheel takes the first and biggest hit. Tremendous heat is generated on the friction surface of the flywheel – especially if slipping the clutch off the line is part of the race program.

Stock cast-iron flywheels are not only heavy, but can quickly overheat, and are not rated to hold up to above stock RPM demands. Think hot shrapnel again. A chromoly flywheel is stronger and can therefore be made thinner and lighter, but the steel surface is harder, which can lead to friction issues. An aluminum flywheel with a steel heat shield friction surface insert gets around these problems, but can create another.

The heat shield has nowhere to expand except against itself, and can warp with extreme heat. This warping creates high spots on the flywheel friction surface. This can cause slipping. The slipping compounds the problem, as the heat created channels through the high spots instead of being wicked away evenly throughout the entire friction surface.

A used up heat shield hoop from an aluminum flywheel shows the degree of warping that can occur. Five to seven thousandths of an inch are all it takes for a flywheel surface to start causing heat and grip issues.