REFLECTOR: High temps

Jim Sower canarder at frontiernet.net
Sat Feb 5 21:50:32 CST 2005


Jim,
Jim Agnew wrote:

>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.
>
Actually, to get "motor" octane (which is how avgas is rated) you want 
to *subtract* about five points from the number you see at your local 
Speedway station.  Like 93 in town is equivalent to 87 in your engine, 
87 in town is like 82 to the plane.  About 60% of aircraft recips (maybe 
80% of flat fours) were designed for 80 octane, so 87 "octane" mogas 
works well.

>  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.  
>
10:1 pistons would  DEFINITELY put Franklin in the 20% that can't use 
regular mogas.  Hi-test might be another matter, but it would take some 
careful research.  Electronic ignition with a tuned down advance curve 
might help, but that would cost you a little power.  You'd make that up, 
of course, with substantial savings in maintenance and engine life 
compared to 100LL.

>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
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