The 5.0L V8 turbodiesel from Cummins that powers the new 2016 Titan XD is a monster of an engine consider that its 555 lb-ft of torque will be powering a half-ton pickup truck. It also features a unique Cummins M2 Two-Stage Turbocharger that works in four modes to boost both high and low engine speeds.
It's a series-sequential turbocharging system that has two different turbos in one unit, using the smaller to facilitate low-flow requirements and the larger for higher flow. This gives the dual advantage of having a smaller, faster-response turbo for the lower end and a higher-volume, larger turbo for the higher end, eliminating most of the turbo lag traditionally associated with large block diesel engines.
A patented rotary valve controls the airflow between the turbochargers, opening ports that allow bypass or waste gate functionality with exhaust after-treatment thermal management. It's a complex-sounding, but relatively simple system that gives the big V8 Cummins its long torque curve.
The video shows the four modes the turbocharger unit acts within. High-pressure mode provides maximum airflow and bypasses many of the other systems to avoid bottlenecks. In Low-pressure mode, the unit uses different routing to push smaller volumes of air with a smaller fan along with exhaust gas mixing for reburn. Wastegate mode offers maximum power for high-torque requirements, such as when starting a load pull or climbing a hill under load. Finally comes Regen mode.
The video shows how the systems work, how the bypass valves move airflow, and more.