Rick wrote;

Wider spacing between the core tubes, double to test.  This will allow

more

air to pass because the boundary air around each fin is restricting air

flow

through cooler.

Al Gietzen wrote:

Wider spacing between tubes certainly reduces airflow resistance; but at the
expense of heat transfer.  You lose area of tubes, and have a larger
temperature drop in the fin as it carries heat away from the tube.

 Optimum tube and fin spacing depends on the configuration and radiator
material.  If the intake is large relative to the rad you have high air flow
rate but less pressure to work with; so you must have a more open core
design (translate larger, heavier rad).  With intake say about 5 times less
than the rad area you convert a lot of dynamic head to pressure which can be
used to push the air through a more densely packed tube and fin arrangement
for more area, and internal turbulence for better heat transfer.

Al

I might add to what Al said in that to cool at 70 MPH you are looking
at only .07 psi air pressure with a near perfect diffuser that converts
dynamic head to pressure. It helps if the intake is in the higher speed 
prop blast. Maximum prop blast occurs about half way out the blade.

Paul Lamar
 
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