As long as you do a few runs each of before and after coastdown testing, then you are a scientist and I will listen. Otherwise, you're just a guy building a Chia car and shouting about random fluctuations in your fuel log.
Vortex Generators have been covered at length in other threads, and they can be used effectively on the trailing edge of round objects, but that's it. Elsewhere, they just increase drag and frontal area. But again, if you don't believe the other scientists here, run your own trials.
Here's a case where a car's underside was originally covered in vortex generators. Covering them up reduced aerodynamic drag 10%:
http://ecomodder.com/forum/showthrea...ges-13199.html