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...
How to Make Key Adjustments to a Drag Racing Clutch

How to Make Key Adjustments to a Drag Racing Clutch

Text by Sam Logan: When we first take an interest in drag racing we soon realize that nothing in its mechanical history is more absorbing than the racing clutch and its operation. Multi-disc drag racing clutches are constructed in four or five different diameters. They range mainly from 6.25in (500cu-in Pro Stock) to 10in (Mountain Motor Pro Stock). Comp Eliminator and sport compact classes often run 7in twin-disc clutches while other engine sizes use 8 inches. Mountain Motor clutches comprise two discs while Pro Mod and Pro Nitrous use three. Obviously the object of these clutches is to transmit formidable engine power to the manual gearboxes and to the rear wheels, but also they must provide predictability and adjustability. Modern billet drag racing clutches feature five principal adjustment mechanisms. These include provisions to address the following: clutch disc wear; static or base spring pressure; centrifugal pressure generated by counter weights, which are positioned on the clutch levers; throw-out bearing distance from the clutch levers; and the air gap, which is the distance that the cover assembly separates itself from the clutch plates. Of course launch RPM could also be considered an adjustment mechanism. Clutch disc wear causes the clutch levers (the fingers) to move from their optimum operating position toward the release bearing. Adjustment is made by inserting a pin punch in the small holes and rotating the upper barrels of the titanium stands. This adjustment, which is made each time the clutch is installed in the car and sometimes between runs, returns the clutch levers to their proper operating position. Static or base pressure is altered by increasing...