I can't disagree that blocking from behind has benefit, but being an avid aviator I can say assuredly that a hard smooth airfoil is far less draggy than air filled pockets. There will be turbulance generated at the edges of the pockets and that spells drag.

However, most home external grill blocking is an inexact science. Really you need to do wind tunnel tests and lots of experimenting to tweak out the aerodynamics. We're just filling in the holes here, not much aerodynamic redesign (in general) so it probably isn't a huge improvement over blocking from the rear.

I actually like a custom look myself, and to be fair that was part of my decision also.

Just my 2 cents

grill blocking looks like a good idea :thumbup: , and I want to eventually try it. My only concern is about allowing enough cooling air to still get thru to keep the electric fan from coming on more than usual. On my little car that fan really drags the engine down thru the alternator when it comes on. I could see a point where a grill block's aero gains could be canceled out by a larger electrical load. This would probably happen at lower speeds where the aero would have less effect anyways. If it is really warm out it could happen at higher speeds. Each type of car would be different, and in each type of climate. It would be interesting to test FE loss from the fan running vs gain from grill block aero. I like the idea of movable louvers for the grill block, like I saw in another thread here. Heck, my 55 allis chalmers could come with an optional movable louvered front grill for cold weather use (not too much for aero since it only goes 14mph:D ).

I recently blocked off the lower part of my grill, I already had the upper part done. My last tank was almost all short city trips bad weather, so didn't see any gains.
Now with some better weather and slightly longer trips I am noticing a difference. My engine temps are higher than normal for winter and its helping FE, I just went 30 miles today almost all city, when I got home the SG read 30.8 for the day, This is really impressive for winter in my car in city driving, I noticed my temps were up over 200f at times, this never happened in winter before, so I think most all the FE gain is due to warmer engine temps and not areo improvments.

I have a grill bock on the outside of my bumper, (I did it in black plastic, and you don't notice it) I left a 4x4" hole right in front of the radiator and the only time I noticed the fan come on was when it was 100+ degrees outside, and I was doing alot of stop and go driving.
I have a feeling that I might have quicker warm up times if I made a smaller hole, but then I would have to remove it in warmer weather.

the main arodinamic reasoning is that the underside of your car is not arodinamic, and the less air you have going under there, and the more you can evacuate that air that is already there, the less drage you will have, some people drill holes in their rear bumper to let it "vent", but that is already really far back, at that point you are better off, in my mind at least, to just keeping as much air from going under in the first place.
and as far as having the grill block behind the grill rather then in front, the leading edge of any shape you want as smooth as possible, you can make the trailing edge to creat turbulence, but the smoother the leading edge the better, but if it's a choice of a grill block behind the grill to prevent air flow thru the engine compartment, and then under the vehicle, or not having one at all, I say go with a grill block on the back side.

Didn't use the stretch plastic - instead tonight I filled the grill openings with white 1/2 inch shipping foam - seems to work great - engine reached 190 in 19 degree temps with the heater running on low. Outside temp according to weather is 10 degrees.

https://memimage.cardomain.net/member...96_32_full.jpg

This is how I blocked my grill. I made a block off plate out of aluminum and covered the center section. The car ran hotter than stock so I extended the air dam an inch and a half or so, you can see that under the bumper. I noticed an improvement of about 5-10 mpg. I am sure this is all aerodynamic because ultimately the temperature is not any hotter than stock. The car felt a little more stable on the freeway as well judging by the increased steering effort.

Nicely done, hotroddr. That's very clean.

Hey hotroddr, don't forget to introduce yourself to the forum!

do you use acetone also?? :rolleyes:

this is the kind of grill block that I like seeing, make it blend in to the look of the car, keeping it clean, and simple!