Do a search on that subject. It has been discussed several times. I have seen everything from 5 to 7 horsepower listed for the pipe and around 1 to 2 horsepower with a K&N and rejetting. That's really good considering that a 400EX only gets around 2 horsepower with a pipe change.

 

also.... does anyone know if FMF or anyone else for that matter have a "quiet series" pipe?

OR... has anyone modified their stock exhaust??? and if so, could you notice a difference?

 

DSAPP- You should get 2 or 3 hp all around with bigger jumps here and there. Buy the way most rappys only get the same. Most pipe builders do not tell the whole story!

 

Check out the dyno sheets in WP's posts.
If I remember right the Z got about 5 HP with the pipe only.
The Z's are realy bottles up when stock. You even have to rejet with just the air box cover removed. The Z is one of the best 4 strokes to hop and get the most bang for your buck.