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 circular and spaced around the cylinder centerline in said cylinder head. One or more spark plugs (or other suitable ignition devices) are provided in the head on the cylinder centerline and/or between pairs of adjacent valves. For best results, the two intake valves have substantially equal diameters. Preferably, the ratio of exhaust valve diameter to intake valve diameter is from about 0.95:1 to 1:1.2. The head typically has three substantially hemispheric depressions each housing one of said valves. Squish areas are preferably provided around said combustion chamber periphery. The piston surface may be at least partially planar and may have an angled or radiused periphery or may have a central recess corresponding generally to the 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. Other fuels and other fuel ignition systems also benefit, such as diesel engines.