I won't get into the watercooled vs. aircooled engine quagmire except to say
that differential expansion due to differing amounts of heat cause asymetric
expansion in the engine and thus make the cylinders "non-cylindrical".  One
engine monitor company I spoke to had measured the differential in heat in
one installation that had a 100 degree F difference from the (right side)
sensor on the 2 o'clock than the 10 o'clock, (the higher temp).  This would
vary from plane to plane but the point is that the aircooled engines all will
have a larger difference from the hot areas to the cool and the Tg is going
to play Havock with the differences between the two.

I too was pretty smug in how "superior" I used to feel with our existing
technology compared to the 50 year old basic engine designs that planes still
use now.  Until I got into it a bit more and realised those guys back then
had a lot on the ball!

Dan Newland

ES#61