One of the factor that influences optimation of performance of diesel engine is an imperfect combustion in the combustion chamber. To optimize performance of this engine it is necessary to do modification by increasing air temperature and air pressure into combustion chamber. A change of inlet air temperature in the combustion chamber will effect the air density, so will influence the amount of air in the combustion chamber. The increasing air pressure into the combustion chamber will help the mixture to reach its combustion condition faster. So that combustion deceleration, specially in the high rotation speed condition can be avoided. The result of the research showed that the optimal condition can be achieved at the temperature 50°C and the pressure 3 bars.