Originally Posted by 472caddychuck
how important is it to have your radiator blocked off from the rest of the engine bay? does it increase performance? or does it just prevent the engine from exploding?
YES. You want to make sure all the air coming in the grille passes through the radiator, not around it, over it, or under it. You also should seal from the bumper to the radiator bottom so that when idling the hot 200* engine compartment air will not be drawn back into the front of the radiator. Don't forget to seal from the radiator top (core support) to the hood. Most assembly line cars had seals there.
A fan shroud and good thermostatic fan clutch will insure that all the airflow possible will be drawn through the radiator.