: Detonation is NEVER a problem when the octane is correct. If the engine
: is designed for 80 octane, it will happily drink 80 octane mogas or
: anything else that meets the minimum spec. The absence of lead in the
: fuel simply means that there is less junk to scavenge out of the
: combustion products.

That's not completely true. Some engines are marginal on their rated fuel (in
particular, fire-breathing TGSIO-ABC-XYZ-540's putting out 350 hp or whatever). Even
some planes could be marginal on their rated fuel in the worse possible condition.
For example, long climb, just under redline CHT, fuel at the bottom of the permissible
octane rating, carb float/jets at the leanest possible configuration, etc, etc.

The bigger variable is that autofuel does not use quite the same rating as
avgas. Autofuel (in the U.S. anyway) uses an (R+M)/2 rating, or anti-knock-index
(A.K.I). The point spread between the two is not published, but is generally about
\pm 5 points, with the lower (motor) most closely similar to the aviation method.
Basically, that means that 87 AKI autogas is probably about 82 motor, 92 research.

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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