Honestly if you're looking for performance why oh why did you buy a 323??? Why didn't you buy the 330 or 335? The amount of money you will spend to add hp here and there will cost way more, and I mean WAY more than the premium for purchasing the more powerful car to begin with. Not to mention if that isn't enough power then you could add the same upgrades to those and gain even more! Too many people buy the base model and say it was all I could afford or I'll modify it and so on without really thinking about it. If you can't afford it, don't buy it. Buy last generations top model instead of the current generations bottom model and be way better off.
SELL YOUR CAR, AND BUY THE ONE YOU SHOULD'VE BOUGHT FROM THE BEGINING!
BMW 325I E30 Chumpcar Race Car
BMW 540iT M-Sport (New Family Hauler)
BMW 135i Msport Daily/track toy