You have to consider the smaller operating range when running LOP. Small
changes in altitude, temperature, or pressure will wider fluctuations in
temperature when running LOP as opposed to ROP. We would all like to think
we keep the engine perfectly leaned, but over the 2000 hours on a typical
engine, how many times does the average pilot let the temperature drift a
little before catching it. How long at 25 or 15 LOP before you shorten the
engine life.
I change altitudes a lot, and tend to fly high when weather permits. I also
have a turbo arrow with a very sensitive throttle that needs to be adjusted
continuously during climbs and decent. I don't need the aggravation of
having to adjust the mixture 3 times as much because I was LOP. I know
during the 2000 hours I would eventually get distracted in busy airspace,
and end up running too close to peek during a cruise climb.

"Michael" wrote in message
oups.com...
So much depends on quality information about proper engine
operations, yet there appears to be little science behind the assertions.

You are quite correct - there is very little science here. There is
certainly a lack of solid statistical evidence. In this situation, you
pretty much have to work from engineering first principles.

Let's start from what is scientifically defensible:

Operating 50 degrees LOP vs 50 degrees ROP (which is what many
manufacturers recommend) means that:
The engine runs slightly rougher. Extra vibration.
The peak pressures in the cylinder (and thus transmitted to the
crankshaft) are lower. Less stress on crankshaft, bearings, etc.

That's about it. Everything else is rumor, conjecture, and guesswork.

The slightly rougher running may in the end reduce the life of the
engine more - or less - than the higher peak pressures in the
cylinders.

Oops, I guess we're done until an actual controlled study shows us
which factor is more important.

Michael