This counterweighted flywheel is designed for externally balanced 454ci big-blocks. Its lightweight design reduces the engine's rotating mass and improves its throttle response. This flywheel uses a 10.4" diameter clutch. Its ring gear outside diameter is 12 3/4". Flywheel ID #3935411. Approximate weight 15lbs. Technical Notes: This flywheel is unbalanced; do not use with internally balanced engines. Use with counterweighted balancer P/N 3963530. 153 tooth starter ring gear. For use with Mark IV engine only.