Tom, IMHO this duct is restricting some of the flow out
the back of your rad. According to K&M it is too close to the
rad. I would try removing it and put
two vents one on either side  on the top of the cowl as far
outboard as you can get. There is a high pressure area at the base
of the windscreen but it rapidly becomes low pressure
as you move out to either side. This is because of lateral
air flow induced by the high pressure in the center of the screen
forcing some of the air to flow around the sides of the cabin.
As this air flows over and down the sides of the cowl a low
pressure area is generated. Good place to vent the cowl.

Do you need a picture?

Also it is real difficulty to do R&D on the cooling system
just using the engine temp. I would build a water manometer
and do some pressure measurements ahead of and behind the rad.

BTW that is Jerry Hey peering at Tom's 3 rotor installation.

Paul Lamar

Tom here is a picture of the pressure distrubutuin on a P51.
Air flows from a high pressure area to a low pressure area.
A side by side cabin would be more pronounced.

Paul Lamar

 
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