These Super Damper standard harmonic balancers from ATI are designed specifically for high rpm engines. Designed and tuned to eliminate harmful crankshaft harmonics that cause parasitic horsepower loss, the proven elastomer design is actually two dampers in one--a 4 in. inner diameter and an 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 rpms.