Originally Posted by SfValley335i
Probably because they can keep using the same exhaust from the n54 135i.
This. Bmw is not going to entirely redesign something if they can help it. This helps the bean counters stay happy :-)
this also means someone could put the N55 exhaust on an N54 car...with no more secondary cats in the i models, it could be a cheap way to upgrade to a more free flowing factory exhaust.