Holger Stephan wrote:

With an unducted radiator you can't slow down the air for a more
efficient heat transfer. The flow is also not both fed at a high
pressure area and released in a low pressure location. Finally, with the
radiator not perpendicular to the air stream the drag will go up unless
the fins are inclined. This point was already made, but do expect
another addition in drag without a special order radiator.

- Holger

None of the configurations proposed here are in the category of an unducted
radiator with the possible exception of some of the guys using evap cores
with large openings.
  
However millions of trucks and thousands of WW I airplanes successfully 
used unducted radiators and they cooled fine. The myth of slowing the air 
flow through the  core to ostensible improve the heat transfer is actually 
counter productive.

Paul Lamar
 
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