A flow model is developed by a finite difference method to analyze the flow in the chamber type intake manifold. The model is based on one dimensional compressible unsteady flow. To obtain stable and accurate solutions, the appropriate boundary conditions for the intake chamber, intake ports and cylinder are formulated.In order to verify the simulation results for the flow model, the calculated results are compared with the experimental measurements. By analyzing pressure waves in the intake system, the optimum intake chamber volume, intake pipe length, at various engine speeds are presented. Finally, the optimum valve timings at different engine operating conditions are sought by this model.