"O. Sami Saydjari" wrote in
:

OK. I have a basic question. Why is running an engine at peak
temperature (as in Rich-of-Peak operation) not good for the engine?
In the scheme of things 50-100 degress cooler than peak temperature
(where many folks recommend the engine be run) does not seem
significantly lower in temperature than the peak temperature.

There is nothing inherently wrong with running an engine at peak, or
ROP, or LOP. The issue is running the engine within the engineering
design constraints -- i.e. where it is not subjected to debilitating
conditions.

There are two temperatures to consider - the cylinder head temp, and the
exhaust gas temp, as well as cylinder pressure. If all three are well
within limits, then you are not hurting the engine. If they are getting
near (or beyond) limits... not good. Add in the fact that most
manufacturers tend to want to stretch the limits on temps in the POH,
and add in instrumentation error (especially with EGT), and a little
margin is a good thing.

In your turbo Arrow III (nice plane, fly one myself) you can run ROP, or
LOP (if it will run smoothly), or you can run at peak (see the POH -
this is recommended for best economy). But regardless, you must keep
the temperatures within limits. Running well rich (100 degrees or more)
is one way to help do this - it sure brings down the EGT and CHT. But
it also burns a LOT of excess gas, fouls the plugs, etc. Leaning it out
helps keep the engine clean, and cuts WAY down on gas (same airspeed LOP
in mine, vs similar temps and airspeed ROP is almost 4 gph difference).

One thing to be careful of on that engine -- at LOW power settings (25"
or so), the EGT's can get quite high due to the fixed mag timing.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
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