I know it's old technology, as high antiknock gasoline is no longer needed/available, but
just for the record there is no such thing as 150 octane gas, or 130 octane etc.
There are quite a few octanes, some of which have a low octane rating, BTW. Iso-Octane
was picked as a reference fuel as it did have a high anti-knock characteristic and blending
it with normal Heptane in known quantities was used to establish the Octane rating of
a specific gasoline by testing in the official Waukesha CFR engine, which was designed for
fast and easy compression ratio changes.
http://www.waukeshacfr.com/about
Obviously, as pure Iso-Octane has an Octane rating of 100, so that is the upper limit of the
Octane scale. Iso-Octane, like some other fuel types is very sensitive to small additions
of tetra-ethyl lead [TEL] so Iso-Octane and say, 4cc/US Gal TEL added to Iso-Octane gives a
rating around 108.
So when high supercharge pressures for aircraft engines appeared on the eve of WW2
the newly dreamed up test known as the "octane rating" was not enough and the Performance
Number test procedure was developed. It used the CFR engine [above] for testing but it
was supercharged to various levels as needed.
WW2 was basically fought with 100/130 Avgas wherein the LEAN knock rating was 100 and the
RICH knock rating was 130. The PN scale crosses the Octane scale at 100, in other words a
fuel that CFR tested at 100 Octane would also test as 100PN. So 100/130 would have the same
[knock limited] horsepower limit as 100 Octane gas whereas the engine could be operated at
30% higher power with a RICH mixture before the knock limit was reached. Most WW2 military
aircraft piston engines did not have the throttle wide open at their max HP output except above
the CRITICAL ALTITUDE. So, getting another 30% power was often just a matter of opening the throttle
more [see To The Gate and Through The Gate]
Almost all WW2 era Avgas came from America, and the Brits doctored quite a bit of theirs and called
it 150PN. To understand why you need to know the difference between MILD and SEVERE
engines. The Brits used a lot of liquid cooled Merlins in combat [they had lots of good air
cooled types, too] and USUALLY liquid cooled engines were MILD while air-cooled were
SEVERE. This was because of the 1/3 rule.
Lastly, claiming the Germans had better aircraft engines than the USA/Britain is not borne out
by the facts. Needless to say, the Germans turned out decent stuff but, believe it or not, their
bureaucrats were far worse than ours at that time in history and beside, our man in Berlin assured
us a win. He made sure no long term designing or planning took place. That is why the Mercedes
and other V-12s needed far larger displacements [and weight] to get the same HP as Allisons and
Merlins. Their main supply of gasoline came from coal gasification, an advanced production method,
but they didn't have the fuel quality needed for high boost pressures.