Have you ever driven a car with open exhaust, especially open manifolds, it's darn loud and not a good loud either, it's kinda of a nasty loud. And like the others said you will have cops following you a few seconds you pull out on the street.
Shoot, my car has duel 3 inch flow masters on it and it drives me nuts driving it around, I wear ear plugs for trips over 15 miles or I will be about deaf at the end of the trip.