The thermal efficiency of a three-rotor rotary engine (RE) was improved by a reduction in the pumping losses. These pumping losses were reduced by using a new port mechanism.The port mechanism utilized was an indirect recirculation type of late intake port closing. It was equipped with a recirculation chamber outside of the housings. This chamber interconnected the recirculation ports within each housing.This port mechanism yielded three main benefits 1. A Considerable reduction in the pumping losses. 2. A uniformly distributed air-fuel mixture in each housing. 3. A limited amount of residual gas in the housing. This residual gas was under specific pulsations by the recirculation chamber thus preventing deterioration in combustion under light loads.The above phenomena were clarified by experiments and simulations. The possibility of a reduction in exhaust emissions was also investigated.