Motor State Distributing has set the pace for highperformance automotive components for racing, street, and offroad use. We offer wide range of quality auto accessories.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. Specifications. Size 1.625 in.