Fredrik,

Please re-read my post. I used the words" mostly" and "in most cases" with a purpose.

Most people who install a tuned pipe, on airplanes and racing boats, want them solely for the maximum, high RPM performance. For people who want to maximize a given engine's performance at relatively low rpm, want this low RPM to be the engine's maximum usable range, with props that are more efficient, like in this [link=http://www.supertigre.com/engines/supg0235-man.html]review on the Super-Tigre .91[/link], or the MVVS tuned silence and full length tuned pipe, for their .61-.91 engines (RPM range 10K-13K).

Adrian added a thing about heli (and car and 3-D...) pipes and their tuned RPM range.