Falken

This is an interesting relationship. This is about all I know about it: Longer runners make for a torque peak lower in the rev range, and shorter runners make for a higher one.

Can someone expound upon this?

b'Eight'

At lower RPM's, the air is traveling at a slower velocity so the cylinders / combustion chamber will fill with a lower volumetric efficiency with shorter runners. To increase volumetric efficiency, the longer runners overcompensate for the slower velocity by using a smaller cross section and also by taking advantage of inertia between intake pulses. In some cases, this can give a slight supercharging effect if runner length is tuned properly.

At higher RPM's, volumetric efficiency is a less of a problem because the increased air velocity allows for filling the combustion chamber more easily. The longer runners will then become a negative. That's why these days, two stage intake manifolds are becoming more popular on high performance engines.

There is also the issue of intake stealing too. In piston engines with single plane manifolds, one cylinder can steal air from another. The cylinders don't fill evenly. A double plan manifold isolates cylinder filling equally. I don't know how this applies to a rotary but I'm sure somebody can share if it does.