if you got the cash,
www.kormanfastbmw.com is the place for you. they will build ou a motor or sell you a turbo that will give you about 6-8 pounds of boost. if you have a 1.8 L i think it'll take you horsepower from 138(?) to about 180-195hp. this is a cool way to doit because when you use a smalll amout of boost, you don't really have to remodify your iternals on your motor like springs, pistons, etc.