BMW currently offers a tri-turbo powerplant in the X5 xDrive50d M Performance and the M550d, adding an electrically driven turbocharger for extra low-end boost pressure. To make it a quad-turbo, BMW would add another electrically driven turbo, or could simply add a second bi-turbo to the diesel inline-six.
The quad-turbo inline-six diesel engine is expected to debut in the M750d 7-series sedan in 2016 and is codenamed B57 TOP. The engine could develop more than 400 hp and 590 pounds-feet of torque. The current N57 performance diesel is called the M Performance TwinPower Turbo.
