Like many things in racing, keeping your engine cool is a tricky task wedged between making sure you have enough airflow through your Aluminum Radiator to keep the coolant within the proper range and taping off the grille opening to increase down force and reduce drag. When you boil it down most basic precepts, it's about consistency (and saving yourself a buck in avoidable engine repairs) versus outright speed.
As a rule, you never want to give up any more grille area in the front of the car than necessary. Taping over the grille is one of the few ways you can improve aerodynamic down force and also reduce drag on a racecar. The best way to keep the smallest grille opening is to build the most efficient cooling system possible. That doesn't necessarily mean you can simply install a larger radiator, because if you cannot supply cool flow of air across every inch of the radiator's surface area, you are wasting its capacity.


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