Need advice for slowing my car down consistently.

Sorry, I should have clarified, this is just a temporary change so I can compete all year in a points series. I want this to be a simple change that I can swap back easily and run the normal 6.8's in the 1/8. I'll be switching back next to Pro next year more than likely. Also, I really don't want to spend any money making it go slower; otherwise I might as well use that money and run Pro like usual.