Lycoming's views on best economy settings

On Tue, 29 Jun 2004 12:55:39 -0400,
wrote:

[trim]

Lycoming finishes the graph with the following statement: "Textron
Lycoming does not recommend operating on the lean side of peak EGT."

Yet as their own graph shows, best economy is ONLY achieved lean of
peak. What extremely interesting to me is that the difference between
peak and lean of peak where best economy occurs is only a matter of a
very few degrees EGT.

Remember, when you are cruising at 60% power, you cannot hurt the
engine no matter where you set the mixture control. You can't burn

That since an aircraft engine will not usually detonate at the lower
power. But turbo engines, I've read, may have difficulty...

valves or cook the cylinderheads or cause detonation, it just isn't
producing enough power to do that. Lycoming themselves recommends
that for maximum engine life, cruise power should be limited to 65%
and CHT's kept below 400 F. But since the instrument panel doesn't
include a CHT guage, the only way to avoid high temps is to be way
rich, or at peak EGT or below.

Why Lycoming recommends against LOP operation is a mystery. MUCH
cooler CHT's and less fuel being burned... what am I missing here?
Does the engine run roughly at this setting? Only those who try LOP
will know.

Corky Scott

As for Lycoming recommending against LOP, there was an article in
Flying magazine (p. 74-75, 7/02, inset article, J.Mac) , where there
was some sort of lead crystalline deposit (lead oxybromide) forming in
_turbo_ engines only in LOP operations. That deposit would cause a
"light" detonation, and eventually destroy the engine. The deposit
apparently does not form in normally aspirated engines, regardless of
mixture. Lead oxybromide was also found to harm the rod and
crankshaft bearings.
If true, I would think this would be common knowledge, and pilots
would not have to run to Lycoming for it. And other authorities would
not suggest lean in turbo engines. (Do they?)
Running lean, by a moment of carelessness (pilots have lots of
things to tend to) invites catastrophic trouble in any engine. And
for the pilot to get in that habit in normally-aspirated engines can,
after the pilot upgrades, apparently inflict harm on turbo engines.
Anyone else familiar with this?

--Mike