Rick:
**the exhaust valves on the TSIO-550E can not cool themselves enough while LOP even when power is back to 28/2400 because it is still at 1550F EGT and that makes the exhaust valve so hot that the valve seat has to be wide and perfect to take all the heat ouf of the valve head, or the heat goes up the stem and burns the oil off the stem therefore wearing the stem and guide very fast.**
I don't know upon what data you are relying to make that assumption, but it is incorrect. The hottest mixture for exhaust valves is found at 25dF ROP. LOP mixtures run the exhaust valve MUCH cooler than ROP mixtures. That was first proven by a NACA report in 1943, subsequently reported by Lycoming in 1966 and again confirmed by GAMI's test facilities in 2004. Raw EGT value has essentially nothing to do with exhaust valve temperature.
The major factor in guide wear is related to MANUFACTURING fit, and not mixture management.
Walter
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