Yes, it tells you the pressure above the cooling fins of the engine (almost full dynamic pressure).  Yes I am making the assumption that the pressure below the engine (other side of the cooling fins) is the same as the backside of the radiator.  Is that not reasonable?   The cooling exit is the same in both examples.    Note that the pressure above the engine was almost full dynamic pressure WITHOUT the exit being blocked.  Therefore my conclusion that the pressure differential is NOT lower on the aircooled engine.

Am I missing your point Al?

Tracy

I guess my point was that there isn’t enough information to draw the conclusion.  But if the exits are the same, and the pressure in front of the radiator is the same as that above the cooling fins; then the pressure drops should be about the same.  But of course it varies from one installation to another, rad thickness, fin density, etc.

In any case; I agree with your premise – I have seen no data that definitively supports the conclusion of lower pressure drop for cooling the air cooled engine.  Should one also infer then, that the flow rate required is also about the same – that the higher fin temp does not give a higher delta T to the cooling air?

Al

Al