Here is an aircraft engine by Hexidyne.
www.hexidyneaviation .com

This engine is rated at 60 hp AT 6000 rpm so a PSRU
is necessary
to make it a practical aircraft engine.

Note the useless torque peak at 4500 RPM. A simple
change in the intake
manifold might move the torque peak up to the rated
6000 RPM speed and
probably result in ten more HP. On the other hand
the 6000 RPM breathing
may not be limited by the intake manifold at all but
by the intake
valves that are probably too small.

This indicates a lack of understanding on the part
of this engine's designer
about the role torque plays in an aircraft engine.

Paul Lamar

tim tracey wrote:

So, what you're saying is that anything beyond the
venerable 5252rpm threshold is the aircraft engines'
true useful powerband where HP is higher than the
torque(assuming we don't go into the area of serious
drop-off of either HP, torque or engine life!)? I'm
not arguing, just trying to see the light. Thanks!

Tim

I don't follow you. What is the question? An aircraft engine needs
peak HP. Peak HP is generated by tuning the intake so  peak torque 
occurs at peak RPM. Peak RPM is of course limited by the diameter 
of the prop. Unless of course you want to sacrifice
peak HP for lower fuel burn at cruise RPM.

Paul Lamar
 
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