The area behind the rad in front of the firewall at A according to 
Kuchemann & Weber and Kays & London needs to be opened up and free. 
Come to think of it Hoerner too. They all agree. This restricts 
the air flow through the rad.

There is no room back there so the best thing to do is move the 
oblique rad under the engine if you have room or use two oblique rads
on either side of the engine plumbed in parallel. This then lets
the hot air dump into the cowl freely to find its way out the bottom
if you prefer or better yet IMHO, out the side with cowl flaps
in both cases.

BTW notice in the Fred Moreno cruise calculations a smaller rad can
be made to cool at a penalty in larger intake area, larger exit area and 
higher cooling aerodynamic drag. This relationship is noticeable in Tracy  
Crook's RV4 installation with two enlarged intake areas and two small rads. 
If a large radiator is acting like a small radiator this relationship will 
also apply. I suspect this is the Power Sport case. 

The bottom line is, as we have seen  over and over again, get the air flowing 
through the rad(s) freely first with a proper diffuser intake duct and an open
and free exit area. Use as large an area rad as possible and not too thick. Do 
this before you add more or larger radiators.

Paul Lamar
 
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