The S&S 510C camshaft set is designed to be used with the stock Twin Cam chain-drive system and is an economical way to improve the performance of stock and slightly modified street engines These cams are as quiet as stock but produce significant power increases across the rpm range, especially above 3000 RPM Compatible with the stock splined chain sprocket used in 2000-06 Twin Cam engines, but may be used in 1999 engines if the H-D 2000-06 style splined rear cam sprocket is used (except 2006 Dyna)