By Sam Logan
Using aluminum sheds 10-15 lbs. from the rotating assembly of a conventional steel flywheel, but it is the effect the weight loss has on the moment of inertia – the measure of an object’s resistance to changes to its rotation – that contributes the real gains. The lower moment of inertia in the aluminum flywheel provokes an instant response, delivering not only faster acceleration and deceleration, but also suppressing wheel spin. In addition, the component is not very expensive and the installation process not very laborious.
Aluminum flywheel manufacturers typically design their aluminum flywheels as re-buildable units. Ram Clutches, a competition clutch and flywheel manufacturer since the early 1970s, includes a thick 1/4? mild steel friction insert to dissipate heat faster, maintain a flat friction surface and reduce the likelihood of distortion. Thinner, unground inserts have a tendency to buckle under the severe heat of hard clutch duty. Though replacement inserts can be renewed by the factory, rarely do the flywheels require them. Typically they are resurfaced on a Blanchard grinder when wear exceeds 0.015?, and this resurfacing process could be performed several times over if necessary.
Aluminum flywheel blanks are derived from 6061 material with a T6 temper, and they arrive at Ram’s facility in Columbia, SC in a variety of thicknesses and diameters from 12.5? to 15?. They are classified by their diameter and by the number of teeth on the starter ring gear that encircles them. The most popular blanks are 13.5? and 14?. The smallest of these suit the 2300/2000 Ford (135 teeth) and the largest are used on the big-block Fords (184 teeth). The most popular flywheel for a Chevrolet carries a 168-tooth ring gear and is produced from a 13.5? blank as is a Ford with a 164-tooth gear. The Chrysler unit usually features a 143-tooth ring gear and is machined from a 13.750? blank.
Flywheels provide 50 percent of the friction surface to which the clutch disc mates; therefore, they contribute half of the holding power of the clutch system. Premium flywheels possess four essential elements: a proper friction surface finish, a perfectly flat friction surface, a friction surface parallel to the crankshaft flange, and a fine balance. Approximately 1 in 20 flywheels is endowed with perfect balance; the remaining 19 will display drilled balance holes.
On the edge of the flywheel a groove is machined to accept a starter ring gear and on its back face three button-head securing screws are installed after the ring gear is heat-expanded then shrunk in place. The securing screws offer a safety margin on competition cars by keeping the ring gear from rotating on the flywheel. “If for some reason,” comments Ram’s Pat Norcia, “the flywheel is exposed to excessive heat, perhaps through severe clutch slippage, the ring gear could become loose as the cooling rates of the steel ring gear and the aluminum flywheel differ.” He added that on billet competition drag racing clutches, were slipping is normal practice, retaining screws are essential.
The principal failings on aftermarket high-performance aluminum flywheels are often a steel friction insert of inadequate thickness (usually 3/16?), the omission of a properly ground surface on the friction insert, and the lack of balancing. To survive these hazards here in this series of pictures is how Ram Clutches makes their high-performance lightweight flywheels.
Source: Ram Clutches