S&S® Performance Replacement cylinder heads for 1986-'99 HD® Evolution® big twin engines are designed to be compatible with a stock style flat topped piston. This set has a 76cc combustion chamber that gives a slight increase in compression for great results with most performance cams. Larger than stock 1.900" intake and 1.575" exhaust valves provide plenty of air while maintaining port velocity for good low and midrange response. S&S® high lift valve springs allow the installation of cams with up to .585" lift. Compatible with stock intake manifolds, exhaust systems, and temperature sensors for EFI equipped models