Steve Brooks <steve@tsisp.com> wrote:

> My engine is now running pretty good and idles very well at 1000 RPMs.  My
> only rough spot is somewhere around 1500, it stumbles occasionally.  Mainly
> when the engine is hot.   Now if I could just get my temperatures down
> another 15 degrees I'd have it made.
 
   Steve, I know this may have already been covered, but the
principles were brought back to me very strongly a few days
ago, climbing from Phoenix to Flagstaff (on the road).  A
cooling system temperature that is linked to throttle
position is a sure sign of insufficient capacity.  

(An a side to Rusty, who will understand: new *company*
mini-van - a Chevy Venture - can't make that climb without
turning off the A/C.  Thank you, cheapskates at corporate
fleet!)  

   How many cubic inches of heat exchanger do you have?  
How is the airflow through it managed?  IIRC, most folks
here who are flying are getting the best results with an
inlet of 1/4 to 1/3 the area of radiator.  How sharp of
an angle does the airflow have to negotiate?  Can you re-
shape the plenum to gently "steer" the air into nearly
perpendicular to the radiator surface?  How is the flow
beyond the radiator managed?  Is there room for expansion?  

   Is the heated air competing for expansion space with air
heated by the exhaust system?  If so, your outlet area needs
to be sized up to allow for the combined sources.

Some things to look at.

Dale R.
COZY MkIV-R13B #1254