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From: "Gary Casey" <glcasey@adelphia.net>
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Subject: IO-550 operation
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<<Maybe someone can answer this but, wouldn't you experience some detonation
when passing from -LOP
thru Total lean to ROP at absolute full power?? Even if its only for a
couple firing cycles-a couple is to many IMHO.  On final, I go mixture rich,
props up-Hand to the throttle.>>

Yes, the risk of running high manifold pressure at low rpm is from
detonation since the ignition timing is fixed.  How high is the risk?
Probably not high since the cylinder surface temperatures are low because of
the low power on final.  I personally like the idea of reducing the workload
on a go-around and that would be by getting the mixture rich and prop
forward on short final.  Then there is only one lever to manipulate.  I
don't see the logic in keeping the rpm down and mixture lean as a benefit to
reduce the power and therefore trim change on go-around.  If you don't want
so much power just don't push the throttle all the way in.  IMHO the fuel
control on the Continentals is so crude that a mixture setting is only good
for one engine operating condition.  If you have the engine correctly leaned
for a low rpm, low power descent there is no reason to believe it will be
even close to correct if you suddenly go to full power or especially to idle
condition on the runway.

<<Running 70 LOP or 70 ROP is the same EGT,
where LOP has cooler CHT's.  I can't see HOW this would ever burn a valve.>>

The argument usually given is that even though the exhaust temperature is
the same LOP as ROP, when running LOP there is free oxygen in the exhaust
ready to attack the exhaust valves.  ROP there is very little free oxygen.
Is that a deciding factor?  I don't know, but apparently not.