These Super Damper standard harmonic balancers from ATI are specifically designed for high-rpm engines. Their proven elastomer is designed and tuned to eliminate harmful crankshaft harmonics that cause parasitic horsepower loss. They are actually two dampers in one--a 4 in. diameter inner damper and a 6 3/8 in., 7 in., or 8 in. diameter outer damper in two shells that bolt to the crank hub. These dampers are engineered to all but eliminate worn parts and timing problems. They're tunable in the field, rebuildable, and extremely efficient at all rpm.