BLOX Racing valves are stock-size, standard compression. All valves are swirl polished, feature undercut stems and hardened tips. BLOX Racing one-piece valves are forged out of EV8 stainless steel for maximum strength and reliability. Each valve then undergoes a hardening treatment using black nitride, which provides a more durable and smoother surface compared to chrome coatings.Black nitride provides the valve head with superior protection against wear and corrosion and greatly reduces the amount of friction between the valve stem and guide. The less friction produced the more power gained.