Optimum Intake Runner Calculation By Bowling
Engine volumetric efficiency and power can be increased considerably by
taking advantage of the natural dynamic effects which occur during the intake filling cycle. The kinetic energy of the resonant pulses can be harnessed
to fill the engine cylinder at volumetric efficiencies up to 130%.
When the intake valve closes, a pressure pulse "bounces" back of the
intake tract and then in again towards the valve, and if timed properly,
extra air can be "shoved" in. To use this pulse, the intake port must be the
correct length, and only occurs during a narrow RPM band.
The following calculation yields an simple, empirically-derived range
of RPMs for a given intake runner length (mean). Second, third, and
fourth order harmonics are provided.