Oh yeah the slip on will make a difference, but not as much as the rejetting that is involved with the install of the pipe. If you remove the airbox lid and rejet it would be a more noticable difference. Rather than adding the Slip on, save up a little more and get a full Yoshimura or HMF. Those are the two best headpipe designs matched with there cans for the Z/KFX/DVX400.