Supertech Nissan Skyline GTR R32 R33 R34 RB26DETT 35.65mm +1.0mm Intake Valves Set of 12 We manufacture our racing valves using only the highest quality materials available. We have spent countless hours studying these different materials as well as you applications to create just the right valve. Because of thermal fatigue the proper choice of material will greatly determine the valve performance and reliability. Supertech relentlessly test new materials to provide valves with unsurpassed fatigue resistance. These valves are black nitride coated, which is a hardening treatment that has been steadily growing in popularity over the last several years. These black Nitride coated valves feature harder surfaces and smoother finishes, providing less friction and subsequently longer life.Â