[Bathrone]

Hi Craig.

That figure is an empirical result from thermodyanic lab testing. It is a fact of physics that water is a far more efficient heat exchange medium than air. Corky Bell talks about it in his turbo book, but also another book of mine "the design and tuning of competition engines" (Smith); as well as non car engineering texts.

Sure, there is more complexity and more parts to a water to air heat exchanger. However if it doesnt break and is engineered for the purpose correctly it will always produce more power than a comparable air to air cooler; and it will be able to be fitted into a smaller package.