On Tue, 10 May 2005 20:43:34 +0000 (UTC),
wrote:

Exactly. The absolute value of EGT does not matter... almost all of the
cooling of the exhaust valves is done through the valve seat (and stem in Lycoming).
Thus, the "cold sink" is the cylinder, and CHT is what's important. Lycoming redlines
CHT at 500, recommends 450 as a max, and general wisedom dictates anything under
375-400 in cruise is fine.

Deakin posts a chart from Pratt and Whitney in his "Mixture Magic"
column which verifies this precisely. In the chart is a line
depicting the loss of strength of the aluminum alloy used for cylinder
heads. It starts dipping LONG before 400 degrees is reached and is
plummeting at 450 degrees.

See: http://www.avweb.com/news/columns/182084-1.html

He recommends running at 400 degrees or under for cruise.

Corky Scott