Paul, this would have no use in a tractor but in a pusher it might do some good..
Put a can on the prop hub coming back a bit into the cowl, put impeller fins on it. Some ducting around the impeller takes care of the flow.
Why not resort to an active air system and create a bigger pressure differential?
...Chrissi

Here is a picture of the planetary geared up fan cooled BMW 801-ML radial engine used
on the Focke Wulf 190.

Paul Lamar
 
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