[chris719]

Originally Posted by XutvJet

See page 20 of the B58 technical training manual, the section titled "Closed Deck". The B58 is part of the B "modular" engine family. It's block shared with the B57 turbo diesel.

https://f30.bimmerpost.com/forums/sh....php?t=1171642

I don't know how much clearer this needs to get for you. BMW wanted to keep engineering and manufacturing costs down and designing and making engine blocks is crazy expensive. Instead of having to develop two separate blocks this time around, they developed one that can be shared between the diesel and gasoline inline 4 and 6 B series motors. Since diesels have high cylinder pressures, the block needs to be closed. Simple as that and why they did it.

Keep digging...