A 500 cm3, air cooled, single cylinder, motor-cycle engine equipped with a novel rotary valve demonstrates a gasoline octane requirement significantly lower than the base-line poppet valve engine. Dynamometer comparison tests over a matrix of part-load and air to fuel-ratio test points, at several engine speeds show a markedly lower specific fuel consumption for the rotary valve. A reduction in ignition advance requirement is observed at these test points and a higher output torque at full load. On-highway motor-cycle comparison tests indicate a consistent fuel advantage for the rotary valve equipped machine. The valve lubrication is hydrodynamic and this is claimed to be the first rotary valve with virtually zero oil consumption and no observable wear.