any info on what exhaust produces the most hp or tourque would help any sights with pipe shootout or personal expierance would be great.

 

DMC or WB Promeg works very well with the 400.

 

I can't tell you which will be the best exhaust, because I haven't tested them all and compared the numbers. I can give you some suggestions though.

I know that the White Brothers E-Series and the FMF Powercore IV-2 are both good slip-on silencers. I have two friends with the WB E-Series, and a friend and I have the FMF Powercore IV-2 on our quads. They seem similar in comparison, but I'm not sure on the exact power increase. They both gave a very noticeable increase in torque as well.

I know that if you want a bad exhaust, check out the Noleen full system. I almost bought one, but opted for the FMF due to availability. There is a guy that races on the local SX and MX tracks who has a 440EX. It is sweeeeet. He has the Noleen system. I heard from them that it gave about a 9 HP increase. It's got a really deep, loud sound. That's one great thing about it. You can hear it from across the pits because it has that deep 4-stroke sound. Like I said, it is loud, but I guess you must give up some things for performance like that. Good luck choosing, because there are so many choices out there, it's extremely hard to decide. I know from experience.