Theoretically (sorry, Leon), you need 20GPM to cool the engine if you
have a 30degree drop across the radiators.  Is that right, Al?  
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Like everything else, it depends on conditions.  Here's a data point -
producing 75 hp per rotor (call it high cruise), using 50-50 EG/water, it
takes 12.7 gpm per rotor to reject the heat with a 30 F delta T.  I think
that is a pretty good design point.  For optimum rad design, cooling drag,
blah, blah. . . you'd like a bit lower delta T, and more flow; but hey,
that's about all the stock pump is going to give.

Al