Quote:
Originally Posted by Christ
I'm pretty sure you're better off blocking the lowest grilles over the higher ones, especially if the lower ones are perpendicular to the ground... they would present a higher open area for air to flow into.
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All else being equal (size of the openings), some people say it's better to block upper grille openings if they're likely above the stagnation point (where airflow "splits" between flowing up & over the car vs. underneath).
The thought is that it's better to permit that upward flowing air to continue over the relatively smooth body of the car than to redirect it through the aerodynamically dirty engine compartment & exit underneath the car.
Might as well use air that was already going to end up there (below the stagnation point - probably lower openings) to take care of cooling.