Recommended posi rear end?

well accordin to a 1/4 mile calculator, if my car will weigh 3100 w/ myself in it and a 240 or 360, at 270hp itll run 13.8....its just an assumption. but wut i meant by that was it wnt be the fastest dart, but itll be fast enough to rub my chevy buddies noses in it :bootysha: