Taking a full 4-stroke cycle to be made up of two crank cycles, the intake valve is thus closed for 474° out of a total of 720°, giving a duty-ratio of 65.8%. Therefore, considering the RPM and how an increasing RPM will suggest a reducing time period for the wave to reflect, a
33
range of values is calculated for the lengths of runners required to achieve the effect of reflecting the higher-pressure air onto the intake valves are they open.