Okay, I am really ignorant to the how the bike functions mechanically but I have an 04 r6 and I was thinking about getting a gytr shorty exhaust. Problem is I do not want to lose any low end due to less backpressure. I was reading a thread on the exup and I really did not want to jump in and mess their dicussion up with this question. I have heard from a yamaha shop that my bike has exup. Exup is the motor right but it also has something to do with the exhaust backpressure I thought? They told me I had exup when I asked them the negative and positive features about adding the gytr shporty and the guy said that it would not run right if I took off the stock muffler which I did a while back when i put on a hindle slip on. I quess the question is by putting on anything other than a stock exhaust would it mess up the performance of the bike. Is the exup in the motor or in the header pipes? Once again sorry for the question but I would like to know what I am going to mess up by putting the gytr shorty on. Thanks in advance for the advice!