[E.Roy]

It also depends on the pressure differential between the engine bay under hood, and the external cowl area. If HIGHER pressure is found under hood, then it would work, and likely reduce front drag and lift. Thinking about the wind tunnel smoke vids I've seen, most cowl areas appear to be pretty clean, as though there isn't a substantial pressure increase at the cowl. Testing needed! Interested to hear others thoughts on this

Edit: I bet having a grille block off would make it less likely to work due to less pressure under hood