The Murphy Builders Site

I read the fuel article in Kitplanes. What I got from it is that lead is not
the issue with airplane engines, but octane, and ethanol is definately bad
because it traps water in the fuel which can freeze. It went on to say that
we could run on lower octane gas with improved ignition systems with
variable timing.
How does the 150/160 hp, car gas/avgas relationship tie in? Is car gas only
approved in 150 hp engines because detonation caused by lower octane car gas
is less damaging to those engines? Are any 160hp engines ok with car gas?
Thanks
Jesse





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I haven't picked up the Kitplanes yet but...
150/160 isn't the issue per se with car or av gas. The issue there is
compression. Higher compression increases tendency to predetonate or
knock and higher octane helps avoid this. As long as compression is not
raised above mid 8:1 I believe, high octane (91,92) car gas should suffice
(this from a conversation I had once with Lycon.) I believe the typical
160 "high compression" piston 0320s is higher than 9:1 -- I know it precludes
use of car gas anyway.

The issue of water (from ethanol) is a separate one. Some believe it is
acceptable in Lycomings due to the carb intake routing, not acceptable in
Continentals. I don't think anyone would argue ethanol doesn't add at least
some risk for carb icing -- why the heck would there be carb heat on a Lyc
designed for non-ethanol fuel in the first place. But, I've heard plenty argue
that some ethanol is acceptable if carb heat practices are ardently followed --
and depends on climate too --- but for what level of ethanol I don't know.
It seems reasonable to me to weigh the up/down sides of ethanol against the
longer term up/down sides of lead.

Gas additives (besides ethanol) is yet a third issue.
Gotta go pick up that Kitplanes article!
-Ben

I read the fuel article in Kitplanes. What I got from it is that lead is not
the issue with airplane engines, but octane, and ethanol is definately bad
because it traps water in the fuel which can freeze. It went on to say that
we could run on lower octane gas with improved ignition systems with
variable timing.
How does the 150/160 hp, car gas/avgas relationship tie in? Is car gas only
approved in 150 hp engines because detonation caused by lower octane

car gas

is less damaging to those engines? Are any 160hp engines ok with car gas?
Thanks
Jesse

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