Abstract: The study presents the effect of the coefficient of discharge of intake and exhaust valve for direct injection diesel engine. The main purpose of the present research is to determine the discharge coefficient of intake and exhaust valves in the engine cylinder head of a 406 cm3. The experiment has been conducted using a flow bench model Superflow SF-1020. It is required to know such discharge coefficients, as a function of lift and pressure ratio in the mathematical modelling process at each juncture during the open cycle. The obtained results are dependent on test pressure.