Extreme Black Chevrolet 396-502 (Mark IV) Intake 2.250 11/32 Valve Engineered for high rpm and high horsepower applications. Extreme Black feature a gloss black nitride and are perfect for high temperatures (they run cooler which improves valve life), nitrous, turbo and supercharger applications. For naturally aspirated motors these valves will give you a much greater cylinder flow for good horsepower gains. They start as a one piece forged, high temperature, high nickel, stainless steel alloy. CNC finished to strict tolerances making these valves the choice for the most demanding race classes. The black nitride micro-hardness is higher than the stainless steel base material. No process can match it for surface hardness. Surface finish is smoother than with chromed stems, having less friction between stem and guide. The black nitride reduces power loss due to less valve-guide friction. Nitriding is not a coating, it is a process where it actually becomes part of the steel.