REFLECTOR: High temps

[Jim Agnew]

John, 

Octane is measured at least two ways and I think that you will find that 93
Octane auto gas is very close to 100LL in octane.  As far as 100LL running
hotter I seriously doubt it.  As far as the Franklin goes, if I'm not mistaken
that it has a compression ratio about 10 to 1 so if you are running regular gas
I would think that you are going to have detonation damage if you run it for
long especially under high MP.  The Cessnas are probably about 8-8.5 or less
compression ratio so they can probably get away with it.

Jim

--- John Dibble <aminetech at bluefrog.com> wrote:

> I have a Franklin, not a Lycoming and no temp problems.  Has anyone with a
> Lycoming
> tried a lower octane fuel?  My experience with Rotax engines is that using a
> higher
> octane fuel than what the engine requires results in high CHTs (50 F higher,
> enough to
> sieze the engine).  I think 100 LL is higher octane than any normally
> aspirated engine
> should need.  Several Cessnas in my flying club use 50/50 avgas/regular.  In
> a pinch,
> I have topped off my tanks with regular and couldn't see any difference in
> performance
> or other problems.
> 
> John
> 
> Jim Sower wrote:
> 
> > I am running a LIO-360-C1E and even after a lot of work on the baffling
> > have CHTs around 375 - 400 with occasional excursions to 425 which I try
> > to correct for.  From the beginning, my oil temp never ever budged off
> > of 180, but more recently I have had oil temps up to 210 - 220 on
> > occasion.  I think part of this might have to do with the firewall oil
> > cooler which exhausts right into the plenum - the high pressure air for
> > cooling the cylinders.  There can't possibly be much air flow through
> > that cooler, and I regard it as a significant design defect.  At some
> > juncture (after I get the engine running again and the plane annualed) I
> > am going to exhaust it to outside air under the cowl.
> >
> > Glad I'm not the only one with high CHTs ... Jim S.
> >
> 
> 
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=====
James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying