i got varying degrees of sucess with a besic tuning profile that i've applied to several RWD cars (it works wonderfully on the viper)
1) i drop the front end all the way down w/ hardest suspension up front
2) raise the rear end all the way up w/ softest suspension in the back
3) as much ballast weight as possible, balanced all the way back
4) Always full downforce on the rear, front varys with the car (experiment for best results)
5) NOS set for maximum power
6) Gear it so that your about to run out of gear in 4th as you pass the finish line (blowing NOS the whole time), 4th is usually a good final gear but you may want to go for 3rd or 5th in other cars, you want good acceleration through the gears but you must also remmeber that you loose time shifting, so using all your gears is not always the best
now this is only for RWD cars
for AWD and FWD i have no idea what to do
EDIT: I just checked, and i was able to get consistent low 8's and even some high 7's in the Viper w/ this basic setup