"Greg Copeland" wrote in message
news
On Sat, 22 Apr 2006 13:14:53 +0000, john smith wrote:

How is it that with the same engine, they develop different HP ratings?
R = 160 BHP @ 2400rpm
S = 180 BHP @ 2700rpm
Is there a governor on the R model?

Throttle restriction.

HP = torque*RPM; or h=t(rpm). If a prop is biting more air, the RPM will
be lower as a result of the higher load on the engine. Thus, the reported
HP will be lower. This is a great example of why comparing HP between cars
is usually a futile and meaningles exercise; especially when the engines
are dramatically different.

To confirm the numbers above for the sake of simple, relative
comparison:
R: t=160/2400; t = 0.067
S: t=180/2700; t = 0.067

Seems like the engines are following the same torque curve to me.

For more reading...
http://en.wikipedia.org/wiki/Torque

Greg

Our club recently bought an R that had supposedly been re-propped to be
180hp. I was unsure about this but from what you're saying, it's
possible...