"Douglas Paterson" wrote in message
...
Deakin's advice still falls on the
"witchcraft" side of the equation, in my book, boiling down to "put the
mixture where it feels right.

I believe that the best "science based" information about this topic is
available from the GAMI folks in ADA, Oklahoma
http://www.gami.com/frames.htm

They have perhaps the best instrumented piston airplane engine anywhere and
have collected lots of repeatable data that are the basis for their
recommendations. They have seminars that answer the kinds of questions
you're asking and now offer them online, too. Lots of graphs and tables. I
haven't attended yet, but I plan to.

In another message, you asked about the mixture setting for maximum power.
I think max power is in the vicinity of 25 - 50 degrees rich of peak EGT.
In cruise at altitude, pull the mixture out until the EGT starts decreasing,
push it back in until it peaks, then push it in some more to get 25 - 50
degrees less than peak. That procedure doesn't work on takeoff; the method
suggested by David Paterson in another post is a good one for takeoff.

Running full rich for takeoff at very high density altitude will put you way
too rich and you'll give up lots of horsepower when you need it the most.
Running full rich for low density altitude takeoffs is important because the
engine is producing at or close to maximum power, where cylinder cooling is
needed. The richer mixture effectively retards the timing, which causes the
peak cylinder pressure to occur later in the combustion cycle, which results
in cooler CHT.

Dennis