It totally depends on how you want your power band to be. Longer the head pipe the more bottom to mid and less on the top, the shorter the head pipe the more mid to top end. also some taper up as they go back and some are striaght so do some research and see what people are using for your type of riding also depends on what mods that you plan on doing as well. and also remember all pipes perform different and the pipe that does the best on dynos isnt always the best when they are in the elements or on dirt, its all about putting the power to the wheels right, hooking up thats what we should all try to achieve. in racing its about the fastest lap times so sometimes to much power can hurt you cause you cant control it this rule applies in all racing.
I'm not too awful "sold" on aftermarket 4 stroke exhaust as a big power mod... not to the extent some are.
Maybe it is because I have been around too long, or maybe it is because I have not experienced the right engine/intake/header/silencer combo yet.
I don't know, but what I do know is that I come from the old school... 2 strokes, and with those you can make a MAJOR difference in power output with aftermarket exhaust. With those you get a lot of extra bang for the buck, and you can also alter the power band a lot more.
The 4 stroke slip-ons can sound a lot better and flow better. But on a 4 stroke that doesn't add a lot. As for head pipes and full exhausts, about the same is true. Different shaped headers can flow better and flow differently to alter the power band some.
The powerbomb and megabomb headers seem a bit interesting though. But then again, the little expansion chamber might just be marketing aimed at guys like me who have had 2 strokes?
Anyways, from my old school point of reference, delivery for the dollar just does not seem to be there.
4 stroke output just does not seem to be affected to the same degree by exhaust.
In the past, I have found this means to gain power very expensive per pony.
I think most think that since it sounds a lot meaner that it must be......
Now I have read that on this KFX450R that doing the big 3 is one instance where there is supposed to be a huge gain. And I am not all that impressed with the stock sound. But I think that when I start to mod that exhaust will still be the last thing I do.... and it would be interesting to see how it compares with just intake and a computer. I may be wrong, but I am thinking it will be close to within a couple of HP without aftermarket exhaust.