I consider those CHTs in a NA airplane to be a bit too high. The larger cowl openings may actually have reduced CHT cooling and resulted in higher CHTs. Testing would be required to be certain of that, but it is very possible.

Walter


On Sep 23, 2005, at 9:26 PM, william rumburg wrote:

Engine cooling air inlets on my 320 cowl measured about 3-3/4 inches circular as the molded parts were received. I'm certain they were designed to be four inches and, even at that, are marginal in order to minimize cooling drag. I enlarged them to the four inch dimension and believe it to be a smart move. CHTs for my IO-320 are about 400 on climb out and 360 to 380 in cruise (dependent on altitude and power setting) which isn't bad, but I'd like to see them a little lower.
My only intentional drain of engine cooling air was a 1/2 inch tube to cool the gascolator and electric boost pump; however, when the cabin heat valve was recently discussed, I realized that valve supplied by Lancair exhausts air overboard when closed and is thus a useless drain of cooling air - if it's source is a 1-1/2 opening in the baffling.
Am I correct and would installing a seperate NACA duct to supply air to the cabin heat valve result in lower CHTs?
 
Bill Rumburg
N403WR (Sonic bOOm)