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. Said three valves are preferably round and spaced around said cylinder centerline in said cylinder head. A spark plug is provided in said head on said cylinder centerline and/or between each pair of adjacent valves. For best results, said two intake valves have substantially equal diameters. Said ratio of said area of said exhaust valve to said total area of an intake valve of from about is about 45 to 65%. Said head has three substantially hemispheric depressions each housing one of said valves. Squish areas are preferably provided around said combustion chamber periphery. Said piston surface is at least partially planar and can have an angled or radiused periphery or may have a central recess corresponding generally to said valve region. 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.