LOP: A few questions.

[testwest]

Byron wrote (regarding the "lean 'til rough, then enrichen until smooth" can wind up LOP):

Norm, can you comment on the Lycoming IO-540-S1A5? How does it behave?

I sure can. It behaves as you say, it is quite smooth until well lean of peak, and enrichening back to smoothness parks the engine at least 100 deg F LOP on the richest cylinder. This is a high compression TN engine, basically 1.5 Mooney 200 hp engines held to 29.5" max all the way to FL230 or so. One has GAMIs, the other does not.

[DaV8or]

In all fairness to the ROP fans, Cruiser's attached article does pretty much conclude that running way ROP (maybe 125 deg +) does create the lowest valve temperatures with the broadest range of operation. This may indicate longer valve life. However, the article makes no mention of the associated build up of soot and carbon depostits associated with very rich operations due to the scope of the research. Some believe that valve failures can be caused by little bits of carbon breaking off in the combustion chamber and then getting stuck on either the valve seat, or the valve head resulting in a hot spot, or leakage. In addition, too much carbon build up can be a source of pre-ignition. Then there is the increased soot in the oil... as usual in engineering, there are trade offs.

Take away is- running 30 deg ROP is the worst place to be for your valves and cooler temps can be found either further lean, or further rich, with the rich side producing the coolest temps of all. Also CHT cannot be used for valve temps, cylinder cooling makes little difference on valve temps, timing makes little difference on valve temps. All of this pretty much meshes with other data that's out there.