Ok just got my big gun slip on the other day and put it on my 550xp.....LOVE IT sounds great. My question is I understand what a fuel controller does by adjusting fuel to the efi, but what I dont understand is how can they say a 3 to 5 hp increase just by adding a controller if your bike is already running fine. And I am going to get a K&N or UNI filter and then the controller my other question is would I benefit from the header pipe from big gun also or not and what gains would I get from these mods for this is probably end of the road for performance.