Manley Extreme Duty Series performance steel valves are a great choice for supercharged, alcohol-burning, or high-revving engines. These engines generate a lot of heat and require special valves that can handle that kind of punishment. All valves are made from the best stainless steel available, with chrome stems and hardened valve tips. Extreme Duty Series valves are swirl-polished and fully machined and available with either undercut heads or straight stems.