Charging Z3 1.9

Can anyone tell me how much power can handle Z3 1.9 components (differential and stuff). I am thinking about adding a turbine or a nitrous to my car and I wish to know how much power I can add to my allmost standard car (I have sport clutch that can handle bigger power).
I know Hammann used to have a turbo kit up to 210 HP. Is this a maximum line I can go without more serious modifications?