1Many environmental problems, such as global warming, drain of fuel and so on, are apprehended in all over the world today, and down-sizing is one of the wise ways to deal with these problems. It is significant that a decrease of the engine power must not be produced by using a small displacement engine, so more efficient engine system should be designed to increase the torque with a little fuel.This study achieves an improvement of efficiency for mounting the super charging system on the small displacement engine. As a result, comparing a super charged engine and a naturally aspirated one to drive the same course and laps, fuel consumptions are 2547 [cc] and 3880 [cc], respectively, and an improvement of fuel consumption is 52%.Designing points to mount super charging system is introduced below. 1It can be forecasted that intake air blow-by gas at the combustion chamber is increased in low engine speed because engine for motor cycle is used. Therefore, the valve timing (cam profile) is changed.2Stress analysis and fluid flow analysis were done for the new intake chamber made by powder laminated casting. The sectional area of the new intake chamber is set to become gradually smaller, in order to increase the flow rate.3Inter cooler is adapted, because intake air compressed with super charger becomes hot and it causes a decrease of charging efficiency and an increase of the knocking of an engine.4The fuel injection map and the ignition timing map are optimized for changes above.These changes above made it possible to make higher torques for a wider range of engine speeds, and this leads to low fuel consumption. It is because that coming down torque peak and average engine speed reduce engine friction. In this way, the value of fuel consumption with super charger can be lower than the one with naturally aspirated.