Engine efficiency is directly related with CO2 emissions (GHG) and is increasing nowadays. This growing concern with environment and efficient use of fuels induces the automotive industry to seek the increase the efficiency of all engine systems. Recently, Brazilian Government instituted new Automotive rules (the so-called Inovar Auto), which will also demand increased engine efficiency. Valve timing system is directly linked to all principal performance parameters, like power, torque and fuel consumption and its study can bring benefits to overall engine performance. The use of a thermodynamic simulation model enables exploratory studies to be conducted with low cost and time, with the identification of interesting valve timing strategies. This can direct efforts and reduce experimental work needs and costs.This work presents the study of the effects of some valve timing parameters on engine performance, seeking the best timings for full load engine operation conditions. A thermodynamic simulation model was developed and applied to a hypothetic engine cylinder in order to explore optimization possibilities for valve timing for two extreme engine speeds, under full load. The effects of valve timing on residual gas fraction, volumetric efficiency, pumping work and mean indicated pressure were analyzed, showing the best configuration of valve timing for 5200 and 2000 rpm.