Horsepower vs. Torque

[Colonel]

Aircraft engines are really weird, because they generally
run at one RPM, and it's a very high power setting as a
percentage of the maximum.  So, the horsepower is what
you get from that torque at that one RPM.

However, many other applications of gasoline engines
vary the RPM considerably.  My CBR600RR, for example,
idles around 1,000 RPM and redlines at 15,000 RPM
and rarely produces over 50% of it's peak horsepower.

The peak horsepower of the CBR600RR is achieved at
slightly under 14,000 RPM, but only when you are
drawing maximum torque from the engine.  Revving
the engine in neutral, for example, doesn't produce
any torque and hence no power.

The best metric of an engine, instead of peak horsepower,
is to integrate (or add up) the area under the torque curve
over the used RPM.

Back to the CBR600RR.  If I ride it between 7,000 and 10,000
RPM, the torque produced in that mid-range is actually far
more important than the torque at the peak HP RPM of 13,800.

Gotta look at the torque curve.  It tells you, what you need to
know about an engine.

That's why I love the RC51.  It doesn't have the peak HP of a
I-4 1000, but I rarely can use that on the street - what I want
is torque in the low and mid-range, which isn't reflected by the
HP at max RPM.