with properly sized headers that go into a single 3" system, you'll easilly make 400 crank hp. My Dakota has the worst headers on the market on them. $120 "shortys" that bolt to the factory down pipes...they are marginally better than the stock manifolds, especially since they are about as compact as the factory manifolds. it then flow through some 2" pipe that dumps into a 3" single run that's about 5 feet long.

I put 295 hp and 330 tq to the wheels, so that's up around the 375-400 ball-park on crank hp, and Like I said, my heads are what's holding me back now, not my exhaust.