Larger piping will help up too an extent. OPnce you pass a certain level you start to loose too much back pressure and modern engines are designed to work with a little back pressure for proper operation. The general consensus is that 2.5" is about the best for good torque while still gaining some extra top end. Though i do know a few people that have done 3" and don't have any problems. The idea of larger is better applies more to turbos, where any back pressure is bad.