Black Diamond exhaust valve for Panhead 1948-1965 and Shovelhead 1966-1984, for high flow racing models. All Precision Machining, Inc., stainless steel valves are impregnated b a special German process .002 inch deep and .0002 inch surface buildup to improve wear properties and reduce friction. This process provides resistance to corrosion and wear superior to that developed by hard chromium and electroless nickel plating. These valves are light and the profiles provide excellent flow characteristics and are stellite tipped. Manufacturer