I modified the curve for the third time and I almost have uniform flow 
through the rad. Another 1/8 th or 1/4 inch here and there will do it.

I also added a horizontal  top on the exit chamber as close to the rad
as I could get it. The apparent velocity at the top of the rad increased
if you can believe the pitot tube results. Obviously they are misleading
as the 40 mph blast out the back of the rad is impinging on the top 
panel and increasing the back or static pressure in the exit duct.
I will reconfigure the water manometer to read the static pressure
in that region as well as the true air velocity and report back. 

I also beefed up the sheet metal
on the sharp end where it meets the rad. Since the dynamic pressure
at 2 inches of water is roughly .08 psi over a ten inch length,
one inch wide of .025 thin sheet aluminum the force could be 
0.8 pounds tending to cause deflection and consequently an air 
pressure leak. The devil is truly in the details.
  
Paul Lamar
 
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