:Gasoline engines achieve maximum efficiency when operated at the knock limit. Knock control ignition systems enable an engine to operate in either continuous or intermittent light knock. Laboratory research has indicated it is harmless to run an engine within this range. Experience with knock control engines in passenger cars has shown erosion damage on pistons. Typical examples of knock erosion damage and ways of influencing severity of damage are discussed.Nickel coating has been developed as an effective and reliable technique to protect pistons from combustion knock erosion. Additional benefits of nickel coated pistons include:Reduced piston depositsIncreased wear resistancein the top ring groove.Reduced cylinder headtemperaturesEngine text results and an analysis of engine efficiency increase due to nickel piston coatings is also presented.