There may be a bit of misunderstanding, here.
While PN does represent "Performance NUmber", the
performance being referenced isn't overall engine performance, but the
knock resistance of the fuel relative to a gasoline made up of 100% iso-octane.
Basically. it's a measure of the resistance of the fuel to detonation (knocking).
The energy content of various grades of gasoline is for all intents and purposes identical.
Below the point where detonation occurs, engine performance will be the same for a given RPM and Manifold Absolute Pressure.
In terms of allowable power settings, effectively there waws no difference between the 100 Octane fuel used by the RAF (And the USAAF in the UK, for a time, and the U.S. Standard 100/130 fuel. The numbers that you see published for the R2800 engine in an F4U-1 or F4U-4 are for 100/130 octane fuel. Using postwar 115.145 Octane, basically the same as teh RAF's 150 PN fuel, The R2800 C-Series engine on an F4U-4 could be run at power levels up to a sea level rating of about 2300 HP. (A gain of 200 HP)
The Throttle Gate (Stop) on both Brit and American airplanes was set tp provide a MAP (Throttle controls Manifold Pressure, Prop Governor controls RPMs) corresponding to Takeoff Power. (And Military Power in engines rated by the U.S.)
No matter what fuel was being used, the throttle had to be pushed past the gate (Either by moving the Boost Control Cutout stop on a Brit engine, or pushing the throttle lever through the safety wire stop in the "Gate" of the throttleon a U.S. airplane.
--
Pete Stickney