Yo, Geoff-
Aviation fuel is formulated differently
than it's automotive counterpart.
It's not formulated with acceleration
or high rpm in mind. Most aircraft
piston engines spend their time at
a more or less constant rpm, and
no more than 2,500rpm at that.
"Floor" the average Lycoming or
Continental piston engine suddenly
and you can hear it ping and/or knock
momentarily (sometimes they just
quit momentarily, but that's a "long"
moment if you've just gotten the thing
back into the air after a "touch and go",
believe me!!). And aircraft piston engines
don't run a hell of lot of advance, either.
They are strictly low rpm applications,
remember.
It's vaporization characteristics are
different and under similiar operating
conditions, aviation 100LL "goes off"
(in the combustion chamber) "sooner"
than it's 93PON (96RON) counterpart
(in automotive type use, same engines)
as in "pre-ignition/detonation" when used
identical engines (automotive application).
Aircraft gasoline is formulated also to
burn "correctly" to pressure altitudes
exceeding 20,000 feet (with appropriate
"leaning" of course. Automotive fuel will
too, but not as "correctly"; not really formulated (usually) with these
altitudes
in mind (though formula can be modified
of course, for special use).
As can be seen, octanes notwithstanding,
these are very differently formulated gasolines for very different
applications.
Now, if you could get your hands on the
WW2 purple 140 octane stuff ("rich" mixture setting, if I recall
correctly)
I'd sure as heck would love to give this
stuff a try, aviation formula or not!!
NOW the octanes would certainly make
up for the different formulas to a great
extent!! I mean if it's good enough for
a P-51 at 60 inches of manifold pressure,
it's got to be worth up to 120RON in
a Judson boosted Spridget, for sure!! :)
Cap'n. Bob
'61 :{)
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