Mixture--science vs witchcraft?

-----Original Message-----
From: Newps ]
Posted At: Saturday, August 18, 2007 8:21 PM
Posted To: rec.aviation.owning
Conversation: Mixture--science vs witchcraft?
Subject: Mixture--science vs witchcraft?

250 HP needs about 20-22 gph for takeoff. After takeoff and
throughout
the climb set mixture to achieve 1250-1300 EGT, any altitude. For
landing leave the mixture where it was for cruise. If you need to do
a
go around then make sure to advance the mixture a little as you ease
the
power in.



The engine won't generate 250 HP at altitude will it? Isn't that a sea
level rating based on the pressure of the air available at sea level? So
the 20-22 gph would be for sea level wouldn't it?

At FL180 the pressure is 1/2 of sea level so we can interpolate that at
9000' the pressure would be only 3/4 of sea level, then factor in the
temperature for the density altitude the engine will really breathe.

Doesn't this mean that the normally aspirated engine in the OPs question
will produce significantly less than 250 HP? I'm not going to do the
math because I'm sure to get it wrong and there are many others on here
more qualified than I, so I'm only guessing that we might see 200 HP. If
that's the case then instead of 20-22 gph wouldn't we be looking for
around 16 gph?