4 coats of black sand during the week is definitely not over prepping the tires, the instructions on the can say 3-6 coats per day, up to 3 days a week, you are well below that. With black sand strait uncut, it will leave a greasy feeling on the tire after a few wipes and take longer to dry with each additional coat, especially if the temp is cool where you do your tire work. I like to prep the tires outside when its hot out but in a shady area, the heat helps it dry quicker. Dont pay much attention to the greasy feeling, when it goes away and the tires feel like they have alot of grip is when the tires are cured and ready to run, usually takes a few days after the last coat of prep you wipe on.
Racing on a track like you described, if the track has little or no grip/bite, you could wipe them more coats each day early in the week, say 4-5 coats each day Sunday, Monday and Tuesday, then let them sit the rest of the week and they will have great bite and last for a couple of races on Friday or Saturday, maintaining that bite you wiped/built into the tires during the week, if that makes sense. The more coats you apply, the more bite you are adding deeper into the tire. You can cut the black sand 50/50 with Acrysol or another cutting agent to use the black sand at the track also as a pre race wipe. Is there a tire rule that requires the yellow vega's for your track? I have had better results with Red Vega MBH tires on dry dusty tracks like that, they were very hard to beat and almost a second faster than the yellows on 2 different tracks where I ran them both
