OK here is a typical curve for a 3.5 inch thick heat exchanger.
If I told you what make and model I would have to kill you :-)

The slope of this curve is way too steep for our speed ranges 
and that is why the automotive industry is going to thin
heat exchangers across the board.

Paul Lamar

 MPH   PSI   INCHES H20

   99.8   0.18   4.8
  102.6   0.19   5.1
  105.2   0.20   5.3
  107.8   0.21   5.6
  110.4   0.22   5.9
  112.9   0.23   6.1
  115.3   0.24   6.4
  117.7   0.25   6.7
  120.0   0.26   6.9
  122.3   0.27   7.2
  124.5   0.28   7.5
  126.7   0.29   7.7
  128.9   0.30   8.0
  131.0   0.31   8.3
  133.1   0.32   8.5
  135.2   0.33   8.8
  137.2   0.34   9.1
  139.2   0.35   9.3
  141.2   0.36   9.6
  143.2   0.37   9.9
  145.1   0.38  10.1
  147.0   0.39  10.4
  148.8   0.40  10.7
  150.7   0.41  10.9
  152.5   0.42  11.2
  154.3   0.43  11.5
  156.1   0.44  11.7
  157.9   0.45  12.0
  159.6   0.46  12.3
  161.3   0.47  12.5
  163.0   0.48  12.8
  164.7   0.49  13.1
  166.4   0.50  13.3
  168.1   0.51  13.6
  169.7   0.52  13.9
  171.3   0.53  14.1
  172.9   0.54  14.4
  174.5   0.55  14.7
  176.1   0.56  14.9
  177.7   0.57  15.2
  179.2   0.58  15.5
  180.8   0.59  15.7
  182.3   0.60  16.0
  183.8   0.61  16.3
  185.3   0.62  16.5
  186.8   0.63  16.8
  188.3   0.64  17.1
  189.7   0.65  17.3
  191.2   0.66  17.6
  192.6   0.67  17.9
  194.1   0.68  18.1
  195.5   0.69  18.4
  196.9   0.70  18.7
  198.3   0.71  18.9
  199.7   0.72  19.2
  201.1   0.73  19.5
 
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