The volumetric efficiency for a 4-stroke, single- cylinder, spark- ignition engine is considered.The mathematical model for the gas exchange process was formulated and solved by numerical technique. The mass flow rate, the pressure-time history in cylinder, intake and exhaust pipes, and the volumetric efficiency were calculated. The important parameter affecting volumetric efficiency was the pressure in the pipes. But, the effect of valve timing on volumetric efficiency was small (1, 2)*.The experiments with 3-different cams were performed. The predicted results were compared with experimental data and satisfactory agreement was obtained. As a result, the volumetric efficiency could be predicted with a relatively simple mathematical model.