Hood louver theory
 

I'm still learning this game, so by all means, flame this post. I've searched for uses for louvers and haven't yet found my answer. I have a station wagon that I don't want to grill block, but do want to up the mpg in the same fashion, with minor aero tweaks.

Theory: if the purpose of a grill block is just to keep air out of the engine bay because it causes drag, would louvers in the top of the hood release that air pressure and gain me some of the grill block advantages?

Interesting idea. I know there's a high pressure area at the base of the windshield so that would be a bad place for the louvers you're considering.

Maybe louvers at mid-hood would pull air out of the engine bay as a venturi effect?

This board has some people who actually do know a lot about aero - I hope they'll look and write here.

My guess is - since the engine bay is not at all a clean-path type of aerodynamic environment, any air going through there is better off not getting in the engine bay in the first place. Probably better to push it off to the sides with a bullet-shaped nose and air dam, or let it flow over the hood and windshield where it is relatively unobstructed.

Good point. I was thinking mid hood, like an Evo-scoop or something, and you see race cars with the louvers over the wheelwells also, but your point will still be an issue.

My Volvo 850 is no sleeker than your brick, and the Geo's much more worthy (and cost-effective) of any modifications, so the wagon in reality will probably receive no mods.