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In a message dated 8/8/01 12:23:50 AM Eastern Daylight Time, Michael D Smith
writes:

Why also do the CHT rise so much when going from FL 230 to FL 260 with
everything else keep the same?

Michael, The simple answer is that you're getting up to an altitude where the
air is too thin to carry away the engine heat. It's a law of nature, and the
bane of high altitude aviators since shortly after Orville and Wilbur. Your
turbo-boosted engine continues to produce the same amount of power as you go
up--until you reach the limit of available boost--when the waste gate fully
closes and all available air from the turbos is going into the air/fuel
induction system. Producing this power generates a lot of heat that the
engine must shed into the oil, exhaust, and surrounding air. The problem is
that the air at 26,000 feet is less than half as efficient in removing heat
as it is at sea level. The amount (volume) of air you can blow across the
cooling fins is approximately constant as you go up, but there aren't enough
molecules going by to absorb the heat. I haven't flown my IV-P yet, but
understand from several flyers that engine heating defines the actual ceiling
of the airplane. I'd also note that heat is an absolute killer of engines and
other mechanical and electric things--as you've noted. If you hope to run
your engine to anywhere near it's recommended TBO, don't push the temps, and
watch them closely. Hope this helps.

Bob Pastusek
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