Lycoming conveniently seems to ignore all the radial powered aircraft flying in the '50s where LOP operation was well proven over millions of hours.
I found a document describing the procedures used for radial engines, it is very interesting. They didn't lean by EGT, as I'm sure you know.
The leaning procedure it describes (summarized):
- lean to a 10% torque drop from best power (I think this is pretty close to peak EGT)
- advance spark timing from 20 degrees to 30 degrees for longer exhaust valve life
- Add 1" MP and lean again to the original leaned torque ('m guessing that's about another 2-3% torque reduction)
Wait a minute - advance spark timing when LOP to maximize exhaust valve life? I thought GAMI said LOP didn't affect valve life??
LOP is pretty common in engines trying to extract maximum efficiency. But I think (outside manual mixture control i.e. aviation) it is rare or nonexistent without variable spark timing.
I don't think Lycoming is ignoring radial engines - they just know that there ARE differences.
For that matter, GAMI says that one advantage of LOP operations is slower combustion and lower PCP occurring later - but don't we have people selling ignition systems to advance the spark at cruise power for earlier PCP - exactly the opposite of what GAMI is telling us?
Keeping it cool
The maximum cruise CHT was 470F. For maximum cylinder life, they adjusted cowl flaps to maintain CHT at 445F.
Michael hits it here- how can cooler than peak EGTs and CHTs damage the engine?
The EGT measurement is an average over time measured in the exhaust pipe. I think the value that really matters is the combustion gas temperature at the instant the exhaust valve opens, when the boundary layer breaks down and the high pressure, high temperature gas hits the valve sealing surface. Finishing combustion earlier and extracting energy into the propeller over a longer time surely makes that gas cooler, even if the average over the whole cycle is higher.
And all the chemical reactions in the engine e.g. lead scavenging work better at high temperature.
(The operating procedure notes I found are here:
http://www.enginehistory.org/Operations/R-4360Ops/r-4360ops1.shtml
If you have anything else similar I would be interested to read them)