Quote:
Originally Posted by stonebreaker
WOT or not, it doesn't matter. The length of the pipe is determined by rpm. Pipe diameter is determined by engine displacement.
No, you can't. 2000 rpm is too slow to make use of pulse scavenging in a streetable car.
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The pipe length is not solely determined by RPM. The length primarily is used in tuning harmonics, while cross section has the largest effect on DeltaP, or pressure drop across a field.
The WOT point was made to convey the fact that the calculator was based on assumed figures, including WOT. In reality, at 20% throttle, 1.0L is not even close to 1.0L. The pipe could be much smaller, increasing deltaP, without having much impact on friction, to a given extent.
The idea is to get the fastest flow with the least friction for a given RPM. This means that there is always a compromise between diameter and length. At any length, pulsed flow can be used to scavenge flow on another cylinder, since as the flow expands and speeds up, it's relative pressure is reduced, which creates a sort of vacuum at another opening, drawing against the other opening's exhaust valve.
Harmonics tuning creates a wave-driven effect in which exhaust gasses can be forced out of the pipe at a higher speed by pressure reflection, which also reduces pressure, increasing deltaP (desirable).