Manley Chevy Small Block Severe Duty Valves (Set of 8)Manley Severe Duty Valves deliver the ultimate in strength, reliability, and high performance durability. Engineered for extreme gasoline engine temperatures, these valves are crafted from exclusive materials (XH 428 for exhaust and NK 844 for intake), offering unmatched tensile strength compared to competitive alloys. In fatigue testing at 40,000 psi and 1400F, Manley exhaust valves endured 100 million cycles, while competitors failed after just