Engine bay pressure?

[MazdaMatt]

You've got it figured out. I would say if you are racing, you want the configuration on the left for engine longevity, but if you're ecomodding, you want the configuration on the right. You could even go so far as the block off the outter 2 thirds of the top opening as well as the whole bottom, then seal it as your diagram shows and figure out how to duct it out to the wheel well. With good ducting and 80% blockage, you'll probably end up with the same cooling as no ducting and no blockage, but gain a huge aero advantage.

[NismoMax80]

looks like you guys already addressed options before
http://ecomodder.com/forum/showthrea...drag-2886.html

i still think those blocking grilles and covering underbodies need to give this aspect thought.