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)