Extensive tests conducted by Manley on their Severe Duty Stainless Steel Valves have determined the superior strength and fatique resistance of their XH428 exhaust valves and NK844 intake valves. Manley Severe Duty Valves are a preferred choice for extended use in highly modified circle track engines. Features. Severe Duty Exhaust Valve for Small Block Chevy. High quality construction and durability. Variety of styles for every type of accessoryCompatibility. Fits Small Block ChevySpecifications. Size 1.60