Harmonic Dampers Chevy Small Block 400 engines. The 80001 makes a great damper for high performance street applications. This damper is 6-3/4 inches in diameter and approximately 1-1/8 inches thick. This is one of Professional Products most popular dampers for the internally balanced small block Chevys. It has 60 degrees of easy to read timing marks and engraved marks every 90 degrees. The PowerForce high performance street model weights approximately 8-1/2 pounds. The Powerforce street model is very similar to the much more expensive G.M. Performance malleable iron 8-inch damper except professional Products is made of stronger nodular iron with more timing marks. Has removable external weight, can be converted to internal balance.