If thats a serious question, and not just a joke... It comes from airplanes (originally) and were used to "spoil" the airflow and reduce lift on the plane. On vehicles, they play the same role - they reduce lift (or reduce drag). Note that I did not include increase downforce. An automotive wing is deliberately designed to increase downforce. Most vehicles have wings, not spoilers, although the term is really used interchangeably, and you'll really only hear racing engineers refer to them solely by their proper name. The rear diffusers on the Ford GT (and I believe the GT500) are technically spoilers.
For all pratical purposes, they aren't functional. They're for looks. Unless you're going 150 mph, you won't see any difference.
They perform a minor role in detaching the airstream from the car. As the car moves forward, it leaves a lower pressure area in the space it was occupying so the air rolling over the top is sucked into that low pressure area which can create drag through turbulence. Flicking the air a little further helps but as you can imagine, it doesn't do much off the top of a relatively small spoiler.
And that is why when you see a giant spoiler on a FWD car, many refer to it as "rice". Because it is of ridiculous height and size, and actually hinders performance, drag, and proper down force (because if the car gets up to speed to actually get down force from the spoiler, that will be pulling the front wheels off the ground, giving the car less traction, not more.) So that is why it's silly for a civic to have an airplane wing on the back.
I learned that a "teardrop" shape would actually allow the laminar flow over the top of a vehicle to rejoin "still" air without creating drag. Trouble is, the useful teardrop shape tapers at a particular angle from the largest cross-section of the vehicle. I seem to recall the angle is something like 23 degrees. Maybe not even close, but the effect is that the "tail" of an ordinary-size car would have to extend nineteen or so feet to a point at the rear. Not a useful configuration in any but land-speed contexts.
Dr. Kamm figured if he could make a car present an aspect that "looks like" nineteen feet of tail to the the air coming over the top of a vehicle, he could obtain a useful effect. It worked, and kept the back wheels of some pretty fast cars on the ground along LeMans' Mulsanne straight. Daytona "Cobra" was among those that benefited from Kamm's work, as well as my 1971 Vega; of the two cars I raced at Riverside, the GT coupe was more powerful and accelerated more quickly, but the Kammback (1-bbl carb!) had a higher top speed at both Riverside and Ontario.
http://home.san.rr.com/fsheff/wagon.htm#wagoms
I built an 8-inch high aluminum rear "spoiler" for the coupe, attached directly to the hatch lid's rear edge. tilted to about 40 degrees in slow air, laid down to 30 at top speed. To demonstrate its effect I practiced fifteen or so laps at Ontario to establish lap times and standard lines through the turns, then removed it and ran some more. At the end of the long straight after the first full-speed lap I took my accustomed 110-mph line into the Turn 1/2 right bend and turn, where the left rear corner of the car was usually half a foot from the outside wall. Without the spoiler it was right on the wall, and might have been deep into it: it ground the end of the bumper flat and made a forty-foot-long gouge in the concrete.
http://home.san.rr.com/fsheff/pictures/omsc01.gif
http://home.san.rr.com/fsheff/highCpe.htm
So they do have an effect, even at speeds below 150 mph, but not so much at ordinary driving speeds. I seem to recall that the effect of wind resistance increases by the cube of the difference from 50 mph on up., so by the time you are traveling at modern freeway speeds (80-85 mph in Southern California) there is likely to be a useful effect from a well-designed aero package. I'm convinced my Mustang is better-planted in the front after adding the CDC "Classic" V6 front air dam/spoiler.
What I'd really like to see is a Mustang with a sharp front like the 2004, and a "station wagon" or "shooting brake" Kamm-inspired back like the 1974 Vega wagon. Thatt would be slick and attractive, I think.
For the OP's question... I just installed my GT500 spoiler I got from the ebay guy you are looking for. It is caraccessories123 that I bought from. $95 PAINTED, and another 25 to ship. AWESOME!!! THey only have like, 4 colors at that price, though. I have a Redfire car, so I got lucky there!
If you just search for GT500 spoiler on ebay, they'll come up. They usually use a yellow stang in their gallery pic, and they sell spoilers both primed and painted, so make sure you bid on a painted auction. I have no complaints! It looks great. The hardest thing about the install, was getting the &^%^& old adhesive off the car from the factory spoiler!!
If you just search for GT500 spoiler on ebay, they'll come up. They usually use a yellow stang in their gallery pic, and they sell spoilers both primed and painted, so make sure you bid on a painted auction. I have no complaints! It looks great. The hardest thing about the install, was getting the &^%^& old adhesive off the car from the factory spoiler!!
Invalid Seller's User ID
"caraccessories123" is not a registered eBay user. If you have mistyped the User ID, please go back and try again.
carparts-123 is the seller, caraccessories123 is the name of the STORE. there is a difference between the two when searching.