If you have a dyno where 15hp was gained with a Y pipe alone, please post it up. I don't believe that exists, but they tend to show between 8 and 9 hp on the 1000, which is very respectable for such a low priced mod.An aftermarket y-pipe will see about 15hp or so gains but you MUST run a power commander (or boondocker, etc). I would highly recommend you look up DynoTech Research and pay the $25 or so for the subscription. Jim will have maps for whatever setup you are thinking of running. If you get the PCV from him he will even load the correct map so it will be plug and play. No need to try to make your own maps.
Yeah, running any mods without knowing where the motor stands is a bad idea... If you run without a box, you better be checking plugs, or getting an EGT.Like I said before, check out DynoTech Research...best $25 you will spend. And sorry, my bad, +/- 12 hp gains with y-pipe...+/- 20 hp with y-pipe, pipe and pcv. Personally, I would not run a y-pipe without the commander but do your research and good luck.