Engine Pro’s Nitro Black series of high-performance nitrided engine valves is suitable for two-valve U.S. domestic racing engines. According to the company, up until now this type of valve was only available for four- and five-valve racing engine applications. Manufactured using a five-step liquid nitriding process that treats the entire valve, the strength of the complete piece is enhanced, not just the wear characteristics of the stem. Nitriding is not a coating and does not change the dimensions of the valve but actually penetrates the valve to enhance its strength. According to Engine Pro, Nitro Black valves hold their performance characteristics longer in engines using exotic, oxygenated, and race fuels including alcohols because the nitriding process makes them better able to resist corrosion and deposits.