For best power:
10.0 GPH at 75% power
8.8 GPH at 65% power
7.8 GPH at 55% power
Best power is a term describing the highest power an engine can (or is allowed to) deliver at given conditions and is certificated to do so.
Best power is experienced at full throttle and full rich mixture at sea level (up to ca 5000 ft density altitude). Leaning not allowed, strictly full rich.
Flying high or operating at high level airports (5000+ ft dens. alt.) best power is reached by full throttle and leaning for highest RPM (regardless fixed or constant speed prop if the plane is not moving). Red knob to the wall gives a mixture too rich for best power output at this conditions.
For best economy cruise:
8.5 GPH at 75% power
7.5 GPH at 65% power
6.6 GPH at 55% power
Best economy is a term describing a condition of the engine at flight giving the lowest consumption for distance flown.
This condition is set by leaning the engine to the
peak EGT for the particular power output.
The point here is: if I lean to peak EGT and I am getting 2400 RPM on fixed prop, OAT is 10 degC, then the power output is 65% according to POH (just an example), I have best economy condition. And the fuel flow should be near the lets say 7.5 GPH.
But, I don't see how, for example, a 75% power setting can be applicable to both 'best economy' and 'best power'. I've doubtless got some fundamental misunderstanding here (I'm still a student) which I'd like to clear up.
If you are flying at a setting where your engine is giving 75% power
at peak EGT you have best economy conditions.
Now imagine you just suddenly enrich the mixture to 80 degF rich of peak and pull the throttle a bit. The engine is working in a different regime, running richer but throttled to 75% again. Same power output, different combustion conditions. You can have 75% at both settings. However, this second case is
not best power, because you
throttled down to 75%. The first case was best economy.
PM me if still not clear.
Miroc