toalco, somewhere in this site (just cant find it right now) the kdx was run on a dyno with the stock pipe and the ones in question and charts were provided with the results. I highly doubt pipe alone would give much more than 3 extra hp. Remember, the folks at Kawi have been doing this a long time, and Im sure they know what they are doing when it comes to pipes. The biggest thing you get from a pipe is the ability to direct the power into the area where you want it most, more low end, more top end etc.. but one usually comes at the expense of the other. Just ask yourself what kind riding you do, and you will know which pipe to get and where it will benefit you.. Just my 2 cents worth.