Butch said he ran 14'' and 13"....the 13" for more MPH. We will run the 13" to tuck / squeeze the rears is as far as possible to help keep the rear of the car as low as we can get it.
to get the scoop the way it is took probably 50 trips outside to the grinder to gradually adjust the lower lip. I wanted it as high as possible in the front, but the trick of course is not taking anymore off than needed to conform to the contour of the not perfectly flat hood.