Chris-
Although air-cooling of an engine is a simple concept (the transfer of
engine heat to the air mass flowing over the engine), it does grow complex
considering air flow dynamics and the many variables of a cowled engine.
The 2.25 square inch cabin heat valve represents approximately 6% of the
two 4" circular air inlets and I know its unlikely that eliminating it
would improve engine cooling by that same 6%. It is, however, potential
engine cooling air just thrown away when not in use and would be an easy
check to block off the opening.
I'd like to have CHTs no more than 380 on climb out and 340-360 in cruise.

Bill Rumburg
N403WR (Sonic bOOm)

> Bill,
> <<Am I correct and would installing a separate NACA duct to supply air to
the cabin heat valve result in lower CHTs?>>
>
> Why not perform a quick test to check the impact.  Go on a reference
flight and record; ALT, MP, OAT, RPM, EGTs, CHTs, and the price of avgas.
Now block off the cabin heat inlet.  You'll also want to disconnect the
tubing at the heat muff so that you don't get a bunch of stagnant hot air
in there.  On the test flight reestablish the same flight conditions as
closely as possible and take you readings.
>
> Chris Zavatson