Flywheels: Attributes that are good to know

Flywheels: Attributes that are good to know

by Archie Bosman:   Most high-performance flywheels are created in billet steel or in billet aluminum. The advantage of the billet steel over the original cast iron unit is that, though they weigh the same, usually around 32lbs, the billet steel unit is significantly stronger. Crucially, it remains free of stress cracks and, therefore, safe at high engine speeds and higher clutch clamping forces. In addition billet steel flywheels operate more effectively with modern high-performance clutch friction materials than do their cast-iron counterparts. In comparison, the billet aluminum flywheel has the decisive advantage of carrying minimal weight. Generally it rids itself of half its mass—often tipping the scales at around 16lbs. Lower mass means a lower moment of inertia, which translates to faster response; that is, faster acceleration and deceleration as well as less wheel spin.  Clutch and flywheel maker Ram of Columbia, SC construct their aluminum flywheels from 6061-T6.To avoid distortion they use a 1/4in thick steel insert as a friction surface, which mates with the clutch disc friction surface. To maintain flatness the inserts are fastened to the flywheels by 18 rivets.To overcome clutch snatch or chatter and provide minimal run-out, both steel and aluminum flywheels are Blanchard-ground. The Blanchard grinder contributes a proper friction surface and also ensures the flywheel is ground parallel to the crankshaft mounting flange. In addition, Ram counter-bores the flywheels for button-head cap screws that secure the starter gear ring to the flywheel.Nonetheless, the lightness of the flywheel must be considered in conjunction with the vehicle’s gear ratio and its overall weight. If its gearing is too high and its flywheel too...