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On 4-stroke cycle engines, the authors reported that under certain conditions the cylinder pressure, measured during the suction stroke with a low-pressure pickup, dropped below the critical pressure. Noting this considerable negative cylinder pressure during the suction stroke, the authors devised a Jet Air Suction Port (JASP), which was opened and closed by piston movement near bottom dead center. As a result, it was possible not only to burn lean mixtures steadily, but also to decrease the fuel consumption 10 to 30 % at idle by the jet air flow generated automatically from the JASP. Reductions in THC, CO and NO at idle were also noted.

In order to improve the volumetric efficiency of a crankcase-supercharged 4-stroke cycle engine in the high speed range, rotary disc valves were used at both the inlet and the outlet sides of the crankcase. The effects of the size of the opening and the phasing of the disc valves on volumetric efficiency were investigated and compared with a system using reed valves. It was found that a volumetric efficiency higher than 120 % could be obtained over a speed of 3000-6000 rpm, which was not possible by using the reed valve system. SUPERCHARGING SYSTEMS utilizing Roots type blowers and/or exhaust turbochargers have been used effectively for increasing the brake mean effective pressure of 4-stroke cycle engines. The authors built a prototype cranckcase-supercharged 4-stroke cycle engine, which used the underside of the piston as a supercharging pump, and confirmed the effectiveness of the concept by motoring and firing tests.