When I dragged my Z with my 18 inch Racing Harts, I couldn't get a good launch to save my life. My best time was 13.50-13.90. This was out of 4 passes. I went back the next week with my stock rims mounted on a friend's drag slicks and ran a 13.00-13.25 with a 1.9 60 ft. The 60 ft makes all the difference in the end. This is with a stage IV TTZ at 16 psi boost.