This lightweight 15 pound nodular iron flywheel reduces an engine's rotating inertia and quickens its throttle response. It is designed for internally balanced small block chevy(1985 and older with 2 piece crank seal) & internally balanced (396,402,427) big-block V8s. This flywheel uses a 10.5" clutch. Its ring gear outside diameter is 12 3/4". Flywheel ID #3856579. Technical Notes: This flywheel is neutral balanced; do not use with externally balanced 454 ci engines. Use with neutral balanced torsional damper P/N 3879623. 153 tooth starter ring gear.