Over Square?

[cjam]

Cheers Bevan,
I thought that running too lean was the main cause of detonation, that in combination with the high pressures you mentioned.
What I still don't understand is that people and magazines attribute engine failures to prolonged running at too lean a mixture, yet lots of people post that running lean of peak should be good for your engine.
Is it that un-even fuel distribution that you mentioned, is that it?
I'm not saying you are wrong but it is such an important thing to get right that I want as much info as possible.
The 206 manual says "25 degrees rich of peak below 75% power and best economy at peak, operation on the lean side of peak EGT is not approved"
Can you anyone explain why the manual states that running lean of peak is not approved?
Cheers, cjam

I just did a search of the Lycoming site and found this;

"The engine power (i. e. speed and manifold pressure) and mixture settings recommended in the Pilots’ Operating Handbook (POH) for a particular aircraft model have been determined by a detonation survey. These surveys use special instrumentation to detect and record detonation as it occurs. Based on these surveys, the detonation limiting conditions are defined. Data from the surveys indicate that detonation occurs in varying degrees; it is sometimes possible to operate an engine for relatively long periods in the first minor phase of detonation without inducing damage. Textron Lycoming does not recommend or condone engine operation which even approaches conditions which might cause detonation. The laboratory quality equipment used for the detonation survey is not practical for use in an aircraft engaged in normal flight operations. Without this equipment, the pilot may not know that detonation is occurring, and it is impossible to establish the fine line between the first phase of minor detonation and the detonation magnitude which induces preignition and/or engine damage. For this reason it is imperative that power and mixture recommendations of the POH be carefully observed."
It's clear from this thread that the poor old fleet is getting different mixtures from different pilots, some good points have come out of it though, I for one am learning when I thought I knew what I was on about!

I'm off to fly shortly, this flight I will use rich of peak because thats what the manual says, looking forward to being convinced otherwise on my return.
Thanks chasps, cjam