The piston and intake valves alternate movements produce pressure waves that propagate throughout the intake conduit. Such waves can adequately increase the intake air mass charge to the engine cylinders. In the present work an experimental study on the engine intake valves phase shift was carried out with the objective to analyze its influence on the intake air mass charge. A production 1.0-liter, 16-valve engine was used, with two intake valves per cylinder. Preliminary tests were conducted in a flow bench, simulating the engine intake air flow conditions, and, then, the engine was tested in a dynamometer bench. The results in the flow bench showed that the intake air mass charge is increased up to a phase shift angle of about 30 degrees. From the tests conducted in the dynamometer tests, results are shown for a phase shift angle of 7.5 degrees, with one of the intake valves opening late with respect to the original opening angle.