Interesting rear air flow unit.
 

The other night I was watching one of the cable shows on street racing.

I looking at the rear of these cars and noticed these additions provided ZERO to minimal down force. Hey wait one minute this could be a better solution to clean up the dirty air coming off the back of the car cutting the aero drag coming off the rear deck. :)

Has anyone ever tested one of these for fuel mileage?

project-biting-the-bullitt/installing-ed-quays-sheetmetal-wing

spoilers

It's not so much about creating downforce as reducing lift.

These kinds of boot extensions have been discussed before and can reduce fuel use.

The closest thing I have done is a roof wing on my pick-up truck which isn't really a roof wing but more like one of these extensions (see link in my signature below).

From the article (which is pretty good other than this):
Say what?

The roof wing on my pick-up truck isn't flush like these guys, a leading edge air slot allows some air bleed and I suspect lower pressure (possible faster air flow on underside) which in turn draws the mass of higher pressure air above down, perhaps not straight off as in the 1965 notch-back Mustang.

If I think about it too much, maybe there isn't much flow on the Stang rear deck unlike the roof of my truck which is all flow.

In any case my seat of the pants estimates put the roof wing contribution at 200 lbs down-force at speeds above 55 mph (gas tank location near there, full tank - empty tank equivalent or more). I can feel many of my aerodynamic experiment take place in the 30-35 mph range, so I do dispute the article quote far above quite fiercely

Yes have talked about these conditions before, but don't recall a dedicated thread on the topic.

If you can provide a link to such a discussion it would be greatly appreciated.

Your wing is nearly vertical. The 'stang wing is nearly flat. I can believe that it doesn't generate significant downforce below 175mph, which is not to say it isn't doing anything at lower speeds.

I have three links in my signature, chin spoiler, rear spoiler and roof wing. The roof wing is flat trust me.

The Mustang's length is lengthened with their trunk deck extension, that helps the aero I guess. The air flow over it is minimal at best. Perhaps they get no downforce under 175 and it is not meant as a general statement for all vehicles.

I put this together.
http://i184.photobucket.com/albums/x...ps7rrnrhja.jpg

Picked up the Mustang image here (modified):
https://vector-templates.com/templat...d_mustang/2471

site search:"Bonneville spoiler"

I suspect that the effect comes from providing a surface for the turbulent flow off the greenhouse to reattach.

Also a Bonneville spoiler with endplates constitutes the top half of a boxed cavity.

True, but in this application it's next closet cousin could be a tonneau cover on a pick-up truck.:D

If they wanted down-force out of it I'm sure all they would have to do is add a wickerbill/Gurney flap rear spoiler on it (as on my truck). Lots of drag, lots of down-force.

I take your point. The flat-cab/half-tonneau would be an edge case.

But the OP's question was about fuel mileage.

Has anyone mentioned fineness ratio?

Mustang wing
 

Ford knew what to do.They just wouldn't produce it.
http://i1271.photobucket.com/albums/...ntitled6-3.jpg
Cheating with a decklid spoiler
http://i1271.photobucket.com/albums/...ntitled8-3.jpg
http://i1271.photobucket.com/albums/...itled18_18.jpg
They did better with Torino
http://i1271.photobucket.com/albums/...ntitled7-4.jpg
They got themselves into the same trap with the Fusion
http://i1271.photobucket.com/albums/...itled-13_3.jpg
For serious competition,when their reputation was really on the line
http://i1271.photobucket.com/albums/...itled4-6-1.jpg

Pardon me while I expand this topic a tiny bit. There's some really awesome aero packages for rally cars - LINK - which may or may not help in the mpg dept. I thought this link kind of applies since we are talking about racing wings being re-purposed for mpg. There's ready made bolt on spats, spoilers, wings, vortex generators, etc. Which seem like they would be higher quality finished products than our creatively used lawn edging. Well at a higher price of course....