Originally Posted by propr'one
M52 (328) and s52 (m3) motors have an aluminum crankcase, which makes them better for forced induction. However, you can boost stock e30's. An s52 swap and a FI kit in a e30 would fly.
1. US spec m52/s52 have iron block, not aluminum (z3 has aluminum)
2. Iron is better for boost.
T-Bar, go with M50 or M52. It is easier to boost than M20 (e30 engine) because boost mods are more common.