[Christ]

Once again, the pipe doesn't need to be 18 feet to benefit from scavenging. That's the "ideal" length for a given engine size at WOT flow, assuming (I believe) 100% VE.

In reality, that wouldn't be happening most of the time, and considerations could be made to take advantage of pulse scavenging, although not in the most ideal sense.

Harmonics are a different beast altogether, and can be taken advantage of on increasingly smaller amounts after primary harmonics, but can still be usable by length/cross section tuning.