[E90Fleet]

Apparently partly had to do with turbo lag control (535d stilll has some lag) and turbo heat control ( remember the diesel engines that have the sequential setup have a much lower exhaust gas temperature than the petrol engines )

The high exhaust gas temperature is also why hardly any turbo petrol engines have variable vane turbos. Only main one that has it is the new Porsche 911 Turbo, and it uses very advanced, very expesive materials for its turbos.
Most new diesel turbos on the other hand have the variable vane system.


Some say they also didnt want the power too high, else the non-turbo M3 would have problems