I did the BMS downpipe and BMS intake. Both cheap and work well. I have a thread started with a dyno video of my car to hear it.
Without tune I think you will not realize the full potential of mods.
2011 FBO & meth 135i
7/20/2012 Dyno FBO no meth: 369 whp | 432 wtq Dynojet
BMS | ER | KW | DPE | iCarbon | OEM