7.8 is mid 12's if you only ran 13.0 your dying on the big end
I think the * 1.57 calculation is based on a average 60' time of around 2.1. Virgil 60's around 1.7 or so which really messes up the calculation. An average 2wd truck with his times would be around 8.2 1/8 or 12.87 1/4.