A stead flow test that predicts the performance of the novel internal combustion engine with oval bore is presented. The experimental measurements and analytic results show that the engine with elliptical cyhnder bore is superior ih charge efficiency to the same displacement volume engine with circular cylinder bore because of its bigger inlet and exhaust valves. In other words, the speed or supercharge can be much increased on the condition that charge efficiency is not decreased. Therefore, the high rating of engine can be realized.