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