SCTA El Mirage racing images GOOGLE/bing
 

As part of my trailer research I've spent some time looking at GOOGLE and Bing images for the Southern California Timing Association's dry lakes racing at El Mirage.
Smoke rake wind tunnel images just don't do justice to an automobiles actual wake turbulence.
Images are presented for fastback,notch back,square back,motorcycles,lakesters,and streamliners.
Anyone who has not seen such photos,owes it to themselves to take a look.
These are the 'money-shots.' For the power available at your drive-wheels,on the highway,this is where the majority of your driving cost is absorbed.
After looking,you may never quite think about the back of your car the same way.;)

It's not clear which images you searched for but here are a few.

It's apparent a lot of the cars have functional spoilers. The dust in the wake is not making its way to the rear window, which suggests the airflow is strong there, and not eddying so much as i'd expect. Does this mean the spoiler is pushing the flow back into its "ideal" profile?

Capri
http://3.bp.blogspot.com/_i_AovfzNXg...00/the+691.jpg

Some sort of streamliner
http://motormavens.com/emAlbum/album..._SCTA_copy.jpg

Barracuda
http://www.scta-bni.org/El%20Mirage/...her/0082_2.jpg

XKE(?) bodied streamliner
http://www.scta-bni.org/El%20Mirage/...ars_1/0598.JPG

Model A
http://www.scta-bni.org/El%20Mirage/...ars_1/0036.JPG

Chevy Monza
http://www.scta-bni.org/El%20Mirage/...ars_1/0126.JPG

Americamaro
http://www.scta-bni.org/El%20Mirage/...ars_1/0433.JPG

'52 ish Ford?
http://www.scta-bni.org/El%20Mirage/...ars_1/0296.JPG

pics
 

Thanks Sven7,I realize it's a lot of pages to peruse but there lay the lesson.Thanks again!

spoilers
 

The spoilers are moving the separation point back,capturing a locked-vortex in front of,and above,and providing a inpenetrateble(sp?) barrier in which to sequester the lower pressure of the wake behind and below,producing safe amounts of downforce while cutting drag.
If we could inject smoke at the backlight I think we'd see the vortex.(cars with roof only of course).

So essentially it's using a vortex on the rear window and trunk area to guide the upper air over it cleanly, while creating downforce. Kind of like a virtual Kammback, if you will. How does this effect help the attachment of airflow?

Is there a practical difference between those Nascar type spoilers (Barracuda) and the flat ones (Monza)?

http://assets.sbnation.com/assets/27...ld_Spoiler.jpg

http://media.popularmechanics.com/im...lle-9-0808.jpg

types
 

Both can give the outer flow a place to re-attach to,and then flow beyond there will skip over (you must pay for energy to feed the circulating vortex though!) which is what cuts drag.
The NASCAR spoiler angle will vary from track to track depending on length,bank,and speeds.And they'll change after qualifying runs,once they get into 'traffic' of racing,where the surrounding cars are getting or losing their air.The angles will be a compromise between speed and downforce.
At Bonneville,the spoiler will also be a compromise between drag and downforce with the added variable of parachute deployment.Typically,the drag chutes are angled to fire on an upward trajectory to catch the air above the spoiler line.Wheel traction is a big issue at Bonneville.Some of the cars are so powerful that they can spin the wheels at many hundreds of miles per hour.And at those speeds,if the car gets sideways they become crude airfoils and lift off.Very scary!
Streamliners fire straight back,but they're so clean the chutes have no problem.Terry Nish includes VGs at the back of his Royal Purple streamliner to guarantee quality onset flow to the dual chutes.If they fail,it's very hard on the brakes even if ceramic.He told me( if my memory serves me) that he coasted for 10-miles once when the chutes failed to deploy.