Abstract: Thin thermal barrier coating of a specified thickness of 0.002 to 0.009 inch to insulate the combustion chamber of an internal combustion engine to achieve optimum reduction of transient head flow. The coating is of an optimum thickness to reduce in-cylinder heat loss in the combustion chamber during combustion, thus increasing engine efficiency, specific power output, and reducing emissions. However, the temperature increase is not so great as to adversely affect engine lubricant life or volumetric efficiency. The invention is particularly suitable for gasoline engines as it does not cause preignition or knocking that is generally caused by insulating coatings of greater thickness. In addition, the invention is particulalry suitable for aluminum combustion chamber components. The thinner coating also results in improved reliability and durability by reducing chipping and cracking failure tendencies associated with ceramic coatings.