Hey Check out all these pipes and more at GT Thunder's website He shows a dyno curve of torque and horsepower for al of them on a stock and full race 400EX. I personally would get the White Brothers E-series. It has the most potential for max HP and will work well with any additional mods that you make down the road. Be sure to click on the 400EX Exhaust shootout link.

CT250R

 

I would have to agree with Bubbag. My quad rips with the DMC on it. It is louder than hell though, but i like it.

 

No, work and live in PA.