15.7.3 Pressure Wave Supercharging
The oscillatory motion of the gases in the pipes of high speed engines during intake and exhaust produces a pressure wave which can be used to increase the mass of the charge admitted into the cylinder. If, for example, the exhaust system is so adjusted that a rarefaction is built up near the exhaust valve towards the end of exhaust when the valves overlap, more burnt gases will flow out of the cylinder. As a result of better scavenging of the cylinder, a greater amount of fresh charge will be admitted. A similar effect is possible if the pressure near the inlet valve is above atmospheric pressure towards the end of admission. The higher the pressure, the better will the cylinder be filled with a fresh charge.