Originally Posted by g300d

The GM transmission is designated A5S390R, which refers to its rated capacity of 390NM.

Technique Tuning has a turbo kit designed for 330i automatics, but word on the forum is that they are hard to contact about it now.

Most of the major supercharger kit suppliers like Active Autowerke, ESS, etc, have kits designed for automatic 330i's as well.

All the above kits are de-tuned for the transmission's capacity.

A few pioneering souls are making ebay kits work, now that more is understood about the MS43 engine management system used in these vehicles.