Online Horsepower Calculators

So I enter 260 hp (not much of a teener), 3400lbs, and 2.76 gears and I'm suppose to run a 13.72. So virtually a 318 4bbl, dual exhaust in a Duster with 2.76 gears goes 13.72?? am I not using this calculator right? Guess I never payed much attention to calculators and dynos