Ryan,
I'm not talking about what happens when you're trying to land an airplane. And I don't mean shaping a car to increase down force. I'm talking about ground effect as opposed to free air, when your 10,000 feet up air acts differently than it does when you're 10 inches off the ground. Air does not behave the same around a bluff body when moving close to the ground. When looking at the aerodynamics of a car, you must remember that the air will move quite differently around the car when it is on the road as opposed to flying at 10,000 feet. So just like we don't design airplanes to fly at 2 feet off the ground, we don't design cars to fly at 10,00 feet. Get it?
So what I'm really trying to say is, because it works on airplanes, it doesn't mean it's going to work on a car.
Mitsubishi spent a crap load of time & effort dinking around with VG's with real engineers and real wind tunnels, they were able to gain 2%.....2%. Now how are you gonna top that? With good enthusiasm and a positive outlook?
Really, answer me this, besides the Mitsubishi EVO from a few years ago, what car manufacturer has put these on a production car? If VGs were able to reduce drag, you'd see them everywhere on everything. I suppose you could claim that "Big Oil" is keeping the car makers from getting too carried away with fuel efficiency. I suppose you also believe there are 100MPG carburetors out there too that they won't install.
Put this on your car, they claim it'll double you mileage.
Fact is, there's crap out there and there's things that really work, VGs fall into the crap realm.
Please post your positive results when you have them, you'd be the first to do so. ABA testing please, we all know that YMMV from hour to hour without any changes to the car. And long term tests have so many variables it isn't even funny.
I suggest you find yourself a nice hill to coast down at 40-50mph or so and see what kind of speed you maintain both with, and without, however many VG gimmicks you want to place on your car. Unless you're driving a crate, you will only see a tiny bit worse Cd when the VG's are in place. Certainly Wunguns Fiesta will suffer from any application of VG's.
Here's the
Mitsubishi Thing
I didn't just fall off a turnip wagon Mr. Flight Test Engineer, I'd be behind vortex generators 100% if there was a shred of hope that they'd work on cars. There may be some cars out there with very poor aero design that VGs could help, but they're few and far between, most modern cars are fairly well optimized for what they are. VG tweeks will yield very small positive results at best and smallish negative ones at worst.
Waste your time if you want. Real gains can be made by blocking your grill, pumping up your tires, and lowering your front airdam among other things. Unless you want to radically reshape your car, you're stuck with what you got, VG's just won't do much.