If you run your car engine on 80 octane mogas, it will usually run fine. If
your car overheats, it will start to knock. If you have 100 octane gas it
will start to knock at a higher CHT than if you ran at 80 octane. This is
not usually a problem in a car that has a radiator and thermostat to
regulate the temperature.

In an airplane the same is true. Run normally both octanes are fine. In an
airplane with a manually adjusted mixture being the only temperature control
( ignoring cowl flaps) it is much easier to overheat an engine. If your CHTs
get to high, it will start to knock. With a higher octane gas it will start
to knock at higher CHTs. Therefore, if you overheat your engine, the lower
octane gas will cause more damage than the higher octane gas. Hopefully I
have drawn a clear enough line between the statements that you said were all
true and the conclusion you said was not.

"Jay Honeck" wrote in message
oups.com...
Let me know which of the above statements you disagree with, and I will
find
a reference for it.
I stand by my statement that an overheated engine will be more damaged if
it
is running lower octane fuel.

None of your statements are incorrect, they are merely irrelevant.

Low-compression aircraft engines were designed to run on 80 octane
fuel. Running fuel of higher octane is not going to hurt anything --
but it won't help, either.

87 octane auto gas is perfect for our low compression engines, and
certainly won't hurt them. Using "premium" (or, for that matter, 100
LL) is neither necessary nor recommended.

(Note: SOME mogas STCs do require using a higher octane car gas, but
those are the exception, not the rule.)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"