The trade-off for using a shorter length runner is that as the acoustic waves propagate back and forth, they will constantly lose energy, so as
Figure 13 : Projection of Required Runner Lengths
Vertical Axis: Runner Lengths (cm) Horizontal Axis: RPM
the runner is designed to accommodate a higher order harmonic, and therefore designed to be shorter and easier to package on the FSAE car, it is also suffering the effects of a decreased ability to improve volumetric efficiency through the ramming effect of the acoustic waves.
Figure 14 below shows,