Supertech High Performance Engine Valves, Springs, Valve Accessories, Pistons and Block Guards Valve Guide Set (8 pcs) GDE-T4AG-SM-8 Valve Guide Toyota 4AGE, 6mm stem Intake & Valve Guide Exhaust, Toyota 4AGE, 6mm stem, Manganese Bronze, to be used with smaller oil seal VS-T6SM The 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 nitrided 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, a copper alloy guide is used. Copper has about a 3 times higher thermal transfer than Manganese Bronze.