Sorry to be posting about this again but now you should be able to help me out a little bit more. I have a 2000 gsr with an aem cai. I'm trying to decide what h/c/e to get. Now I have decided that if I go for smaller diameter I will probably get dc 4-1 2.0", 2.25" test pipe/cat, 2 3/8" exhaust. However, if I decide to go for larger diameter I will probably get 2.5" straight through. My question is that I know for sure that I will be doing more mods after the h/c/e just not exactly how much. I don't want to hinder my future mods such as cams and pistons and a lot more power by getting the smaller diamiter exhaust system, but If I get the larger 2.5" straight through and in the future never get around to the cams and everything else will the larger diameter be hurting my performance that much? Also, if I do get the 2.5" straight can anyone suggest any 2.5" exhausts other than hytech or smsp? If I do get the smaller diameter stepped system can I just bolt everything up to each other or do I need something to make the 2.0" collector fit the 2.25" cat and that to the 2 3/8" exhaust?