Variable valve timing is a modern technique that aims to acquire the optimum air capacity at
different operating conditions for internal combustion engines. The present work proposed a
mathematical model to simulate the thermodynamic processes for motored engine including the air
charge flowing through the intake manifold equipped with throttling valve. The pressure waves
propagating through the intake manifold is considered. An experimental test rig consists of an
engine equipped with measuring devices to record the engine speed, instantaneous cylinder and
intake manifold pressure. Volumetric efficiency is estimated based on the experimental data at
different engine throttling valve positions. The recorded data were compared with computational
output in order to validate the proposed model. The model is used to address the effects of intake
valve timing as well as throttling valve position at different engine speeds on the volumetric
efficiency and equivalent compression ratio. The results show the importance of delaying the inlet
valve closing angle with increasing engine speed to insure the best charge. The results show also
remarkable effect of valve timing on the cylinder pressure. When delaying inlet valve closing
angle, the effective compression ratio tends to decrease.