Abstract

An intake and exhaust system for use with internal combustion engines that uses two intake valves and one exhaust valve for each engine cylinder. The three valves are preferably round and spaced substantially uniformly in the cylinder head around the cylinder centerline. For best results, the two intake valves have substantially equal diameters, with the diameter of the exhaust valve having a ratio to the diameter of an intake valve of from about 1:1 to about 1:1.2. Preferably one axial, three peripheral or an axial and three peripheral spark plugs equally spaced around the cylinder axis each centrally located in one of the areas between adjacent valves and the edge of the cylinder. The head has three substantially hemispheric depressions each housing one of said valves. This invention provides a fast and uniform lean burn, permits use of a high compression ratio and lower octane, unleaded gasoline and provides improved thermal efficiency.