Abstract: For the more efficient operation of both spark- and compression-ignited internal combustion engines, and/or control of octane requirement increase in spark-ignited internal combustion engines, at least a portion of the surfaces of the intake manifold exposed to the fuel-air mixture, and/or the combustion chamber exposed to combustion, are fabricated from coated with a material having the combination of thermal conductance and thermal penetration which permits the temperature of said surface during the combustion process to be in excess of the temperature at which deposits form and said surface storing insufficient heat to substantially raise the temperature of the incoming air-fuel charge during the engine intake and compression stroke.