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Date: Tue, 10 Feb 2009 13:32:24 -0500
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Subject: Re: [LML] Re: cylinder wear-to lean or not too lean
From: "John Schroeder" <jschroeder@perigee.net>
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John -

I probably missed a message or two in this thread. But where did this  
quote come from? Max CHT is really not defineable in any useful or  
practical sense at all. My CHT's are alarmed at 400 and from everything I  
have read your do irreparable damage to the cylinder at around 425 degrees  
in an air-cooled aircraft engine. "Max CHT" may equate to "Max Power" in  
some theroetical sense, but the concept is useless as an engine management  
tool.

Regards,

John Schroeder
LNCE

On Tue, 10 Feb 2009 00:50:05 -0500, John Hafen <j.hafen@comcast.net> wrote:

> Here¹s the quote:
>
> ³So as the mixture is leaned, power peaks first, with CHT peaking at very
> close to the same point. In practical terms, if we lean to max CHT, we'll
> have max power for that MP/RPM setting. Doesn't that make sense,
> intuitively? Max power, max CHT? It's not precisely true, but it's close
> enough.²
>
> John
>
>
> On 2/8/09 11:23 AM, "Colyn Case at earthlink" <colyncase@earthlink.net>
> wrote:
>
>> John,
>>     Did they really print that about CHT?
>>     I don't remember that max CHT equates to anything useful although  
>> it may
>> correlate very well to max internal cylinder pressure (ICP), which is a  
>> bad
>> thing.  ...but it's also affected by cylinder cooling, while EGT is  
>> (mostly)
>> not. Max EGT would be stoichiometric which is most efficient if your  
>> engine
>> can take it.   Usually slightly rich of that (e.g. 50 dF ROP) is better  
>> power
>> but also involves more pressure before top dead center and is close to  
>> max
>> ICP.
>>     There's a really scary picture you get early in the APS course  
>> which shows
>> how the internal cylinder pressure varies in relation to crank position  
>> when
>> you are running at "best power".  A measurable amount of the combustion
>> expansion is actually pushing backwards on the crank until it comes  
>> over the
>> top.   Great for torsional stress.
>>
>> Colyn
>>
>>
>