Perry Mick wrote:

Recently Jon Lauter asked why I was using a 24 psi pressure
cap.  I think we need to discuss this.  It was Tracy who originally
advocated using higher pressure caps for high altitude use.  I
think Ed Anderson is also running a higher pressure cap, while
I'm throwing names out.

The 2nd gen RX-7 uses 13 psi caps, the 3rd gen 16 psi.  I was
running a 16 psi cap initially but changed to 24 psi during my
flight test period.  My coolant pressure is typically between
10 and 15 psi, so I think 13 and 16 psi is a little marginal.
I think I'm also running a little higher temperature/pressure
than normal because I have a relatively small volume of
coolant.  This will change slightly in the future when I install
a real radiator with end tanks.

I would like to hear what others are using and think about
this issue.

--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com

Jim M wrote:

        I have been using a 16 lb. cap since I started flying, my pressure
has never gone over 12 lbs. Mind you I also have never had the bird over
9500 ft. either.

Jim mosur
RV6 13B
Brampton, Ontario

Jim has two of these very nice, large area, relatively thin radiators in 
oblique ducts. Correct me if I am wrong Jim, you are also
using a thermostat so you would not know if you were overcooling
most of the time. 

My reasoning goes like this; if you keep it cool enough
the system pressure will never get very high.

Paul Lamar
 
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