Radiators: Is 22" enough for 400 HP?

Seems silly to think that the extra area of a 26" radiator would not get some air flow. Most radiators don't mount flush against the sheet metal opening, so if a 1" stand-off, air will surely spread to flow thru all the radiator. Depends on your exact geometry and one might have to run a CFD model to estimate well. Why does it happen? Back-pressure builds up from the restriction of the radiator, so the air finds other paths of less resistance.