Manley Severe Duty Pro Flo series performance valves are a great choice for your high performance or race engine. All valves are made from stainless steel (intakes are NK-844; exhausts are XH-428) with chrome stems and hardened valve tips. Severe Duty series valves are made of superior materials, are fully machined and swirl polished, and offer improved flow with undercut "Pro Flo" stems.