A series of experiments have been carried out to clarify several problems of the gaoline engine: 1. How do atmospheric conditions affect the performance of automotive gasoline engine? 2. How should the engine be tuned to get the best performance under various atmospheric conditions? 3. What is the best way to correct the observed performance to that under standard atmospheric conditions? How much accuracy will be achieved by this method?Various atmospheric conditions have been applied to a 4-cycle 4-cyl gasoline engine in the laboratory, and dynamometer tests have been conducted at wide open throttle. Results obtained are given and discussed in this paper.