In this study, a four-stroke irreversible Ottocycle model was constructed using the finite time thermodynamics to investigatethe effect of the mean piston speed and the residual gas fraction on the cycle(or engine) performance. Fuel consumption was taken as a function of meanpiston speed, and initial cycle temperature was considered as a function ofresidual gas fraction. It has been assumed that the specific heat does notchange depending on the temperature. A detailed numerical example study hasbeen made to see the effect of the mean piston speed and the residual gasfraction on engine performance. As a result of the numerical example made, thecycle thermal efficiency and the dimensionless power output were observed withthe increase of the residual gas amount and the mean piston speed. We thinkthat the results obtained are especially important for engine designers.