I was just looking through the Sport Compact Car mag and saw that there were these add ons called airtabs. How many would I need to notice a difference in the feel of my 93 Nissan Sentra.
thanks/later/Bruce            

I wonder the same thing.  I have a MINI Cooper.  Given the design of the car, there is a terriable vortex that comes off the back of the car.  Similar to the back of a van.  In the MINI community we've been looking for a solution to the dirty back window that looks cool.  If airtab can be molded onto the roof, we may have a winner.
Also, the project WRX V.08 artical (March 08) failed to show a decent pic after paint, not just a close up during instalation.  

Basically i don't think there are really any aftermarket companies that are going to invest research in this.  Vortex generators are most efficient when the height is that of the boundary layer (where laminar flow becomes turbulent) and that takes a lot of testing.  And the boundary layer is at a different position and height on different cars.  But the main thing is you would have to be going very fast for them to take effect even then your butt wouldn't be able to notice a difference.  But they might look cook, eh?  

I would think that if "airtabs" contributed anything significant to a cars aero characteristics I would have heard of this before now. I understand that the EVO (and various real WRC cars) have incorporated "vortex generators" into its rear roof years ago. The only way I understand this is: the fins are meant to disrupt and break apart mass airflow before it dips down and creates more drag on the trunk/rear of the car. I'm no aerodynamicist but that is literally my only guess at their function, and I also don't see that having any effect until about 80MPH. It seems kind of gimmicky to me, and there are more efficient ways to lower the coefficient of drag.  

I thought it was the opposite. According to the February 2008 issue of Sport Compact Car Magazine, it should push air down the windshield creating downforce. The example they gave was how water coming off a waterfall doesn't go straight down it goes forward and then falls down, where as if you put vortex generators at the edge of the waterfall it'll lower the pressure and force the water to fall closer to the edge of the cliff.  

Regardless of how it works, ptieu, the fact of the matter is this: they will only work like a body kit or a spoiler, meaning the vehicle has to be traveling at high speeds for them to take effect, and when they do, it's not like you're going to feel anything anyways. If it really is a big deal, then I guess you can add them, although I doubt it would really be worth the trouble or effort.  

Mitsubishi has posted the article on vortex generator testing on their website. Here's the pdf:  www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf

Also, I saw small vortex generators on the rear view mirrors of a BMW the other day. I believe it was a 6 series, but I was so interested in the mirrors that I didn't notice how many doors the thing had.    

Wow. I saw it, and.....WOW!... I want some now.....wow...... I wonder if they come in Carbon Fiber?  

I just bought an 03 Focus SVT a couple weeks ago, and it actually has "vortex generators" on the rear of the stock sunroof. Now I just need another 70 or so BHP for all six speeds to feel ballsy. Nonetheless, its the nicest car i've ever owned.