Black Diamond intake valve for Panhead 1948-1965. 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