A point I like to think of is that 50 or 80 degrees "from" "peak" on the rich side and on the lean side is, the same temperature.  For piston engines, running 50 deg lean of peak is the same temp as running 50 deg rich of peak, so the valves are seeing the same temp - so why are some engine "gurus" so adament about cruising 50 deg rich of peak?  It makes no sense to me

David,

 This subject could qualify as a "never ending debate" issue. There are true economys to be found by running lean of peak. But there is a danger if running lean of peak and climbing you can get into an area very dangerous for detonation. Running up the "backside" of the leanness curve can cause overtemps in a piston engine very easily. Exhaust valve failure is a real danger. Rotary wise we are safer than piston pushers since the large amount of heat transfer area keeps us safer. Detonation is still possible so caution is recomended.

My EAA chapter was visited by Lycon a Lyc engine builder of good rep in our area. Steve from Lycon mentioned that there has been a lot of variance in avgas with large changes in formulation form area to area. They tested avgas in several western states and found enough difference that they wouldn't warranty their engines if run lean of peak (at all) although I don't know how they would be able to prove you were operating in that mode!

Bill Jepson