OK, I'm not a production or classic racer, but generally I understand most of the rules....
The rule is there to keep you from directing the air around the engine compartment instead of through it as the manufacturer intended. That would give you an aero advantage. Once the air is through the radiator it does not matter what else you do with it.
OK, that is the way I see it.... lots of folks use intercoolers... now if you are running production and turbo it had to be available from the factory with that combo, you can add intercoolers.
The official word should be obtained from the sanctioning body
