Newsgroups: rec.aviation.student
From: trisoft@realtime.net (James M. Knox)
Subject: Re: Another silly question: why do leaner engines run hotter?
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In article <360A5F27.795C@ibm.net>, snbird@ibm.net wrote:

>True.  But begs another question.  We're told that over-leaning
>damages the engine.  By causing it to run too hot...
>
>This suggests to me that if running too lean damages the engine, 
>the mechanism is not excess CHT.  Does anyone know the mechanism?

Actually, in a normally aspirated engine below 75% power it is almost 
impossible to induce detonation with any setting.  [I know some folks who have 
really tried hard to do so, with a fully instrumented engine.]  The "bad 
feeling" we get from running LOP is not normally detonation but vibration.

OTOH, that doesn't mean that you should rush out there and fly your O-360 at 
50 LOP.  Even ignoring the vibration, the fuel/air mix is too uneven.  If the 
first cylinder to peak is now 50 LOP, then there is probably another that is 
still 50 ROP, and probably two others that are somewhere right around PEAK 
(and running very hot).

The question you raise is right on...  hot is hot, cool is cool - and cool is 
better (with respect to cylinders, valves, etc.).  But most engines can only 
run smoothly *and* cool on the rich side of peak. 

                                                                jmk
