Supertech Manganese Bronze Intake/Exhaust Valve Guide Set of 10Our Valve Guides are precision machined from high quality Manganese Bronze material. Supertech Valve Guides are designed to be used in combination with our low friction black nitride valves to provide the best solution for both performance and durability. For exhaust valve guides designed to be used for high powered engines that need a better thermal transfer coefficient, we use a copper alloy guide. Copper has about a 3 times higher thermal transfer