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 around the cylinder centerline in the cylinder head. The two intake valves may be spaced closer to the exhaust valve than to each other. The two intake valves may, alternatively, be spaced closer to each other than to the exhaust valve and two spark plugs may be provided, each lying between an intake valve and the exhaust valve. 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. The head has three substantially hemispheric depressions each housing one of said valves. Squish areas are preferably provided between each pair of adjacent valves around the combustion chamber periphery. 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.