Grille Blocking Front or Rear
 

I have read many post regarding grill blocks and I myself have done it to the Vibe. I want to do it to my 4-runner also, however will I get the same benefits from blocking the grille from inside the hood as I would just blocking the front side of the grille? In this case the first motivation is aesthetics.

I hope you guys understand my question ...

You'll likely get the same benefit blocking the rear of the grille vs. the front. The difference between the two approaches would be very small (though presenting a smooth face to the wind is always best).

blocking the rear would create a "pocket" of spinning air similar to what you would find in a truck bed. not quite as efficient as a smooth surface, but it would promote laminar flow.

The only advantage to blocking the rear side is you don't get that tacky cheap look.

Hey, cheap gets a bad rap!!! I consider it "theft deterrence". :D

You could always look around the forums and find some of the "professional" looking grill blocks and model yours after that. That way you get the advantage of one being on the front while still having your car look good, but then again you do lose that "theft deterrence" quality, lol.

it would be better in front, if you know someone that can mold plastic you could mold clear plastic and it wouldn't stick out, unless they went close and would be solid.

I made mine a behind-the-grill block so as not to attract the cops' attention. I suspect it works almost as well as in front of the grill; that's what an aerodynamicist at the university told me, too.
The newer BMW's have automatic behind-the-grill block blinds that are at least 3 inches behind the grill, i.e. huge air pocket. It must work, though, or they wouldn't go to all the trouble.

Not everything in a final product is for functionality but a balance between that and aesthetic styling. For example did I really need 2 giant dimples in my fender for non-existant fog lights? I think not. Probably doesn't make a mjor difference in Cd but I don't know how smart it was for divots in the first place though I suspect cost was a factor vs a plastic covering over the divots.

Tooling up to mold a front end without those pockets probably killed that idea, it's not that much more plastic, but the R&D on it, tooling and the production line space to make a separate bumper.