This is fundamental study to improve performance of the SI engine,. In this study a conven-tional kerosene engine was modified to LPG dedicated engine which can be operated with LPG(Liquefied Petroleum Gas) The modified model were tested in accordance with various compression ratios. Also the engine performance with modified model was compared with the conventional one. The results are sum-marized as follow; 1. In comparison with the conventional kerosene Gasoline engine and LPG dedicated engine can be operated with lower exhaust emission better fuel economy and better thermal efficiency. 2. But is produce a slightly lower brake horse power.