S&S heads give great performance, and work with additional upgradesCompatible with stock 3-1/2'' or 3-5/8'' bore enginesFully assembled, and include stainless steel valves and high-lift springs (up to .640 lift)Large 2.000'' intake and 1.605'' exhaust valves and high flowing ports supply plenty of air for big inch enginesMust reuse stock headboltsMade in the USAS&S Super Stock piston kits are required.Intake manifold, pistons and gasket kits are sold separately.