lml@lancaironline.net Mailing List Archive

In a message dated 9/23/2005 9:26:34 P.M. Central Standard Time, lancair403@earthlink.net writes:

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,

Probably not.

In the summer I put a reducer plate over the cabin heat intake in the baffling that reduces it to a 1/2" hole (some air is needed to keep from burning things up). This does not alter the other 3 air takeoffs - vacuum pump shroud, voltage regulator blast tube and alternator cooling tube.

There are so many ways to improve engine cooling - perhaps you should first measure the pressure differential between the upper and lower cowl. If it is at or above 7" H2O, you have enough of a differential. I have opened up the lower baffle in front of cyl #2 and put a block in front of cyl #1. Now #4 is the hottest and it will receive attention next.

Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)