Nissan finally got its truck lineup in gear with the release of the all-new 2016 Titan, specifically the diesel-powered XD model. With a 5.0-liter, V-8, Cummins diesel engine that boasts 310 horses and 555 pound-feet of twist, the Titan XD is right up there with the big three in Detroit. To help this engine produce excellent power throughout its entire rev range, this new Cummins engine uses a unique Two-Stage Turbocharger. To help better explain this turbocharging technology, Nissan has released a video (below) detailing its inner workings.
Within this single turbocharger unit are actually two turbochargers, one large and one small. The small turbo takes less effort to get it spooled up, which helps give the Titan XD the grunt it needs to get that heavy load moving from a dead stop. Once the revs increase and the exhaust gases get flowing, a rotary valve diverts the gases to the larger turbocharger for maximum power.
For anyone who’s driven a car with just one turbo, be it big or small, you likely noticed that there is some sort of compromise with both. A small turbo spools quickly, but it hits it is limited in its total output. With a large turbo, it takes time to get the turbine spinning – this is called turbo lag – and you almost creep off the line until the turbo is at full scream. Once at 100 percent, however, the larger turbo provides significantly more output than the smaller and quicker-spooling one. In a nutshell, this Two-Stage system combines the best of both worlds.
The end result of this technology is similar to that of Chrysler, GM and Ford, but the execution is far different. Chrysler, Ford and GM use variable-geometry turbochargers (VGT), which changes the effective aspect ratio of the turbocharger to allow it to spool more quickly at low revs and deliver peak power at higher revs.
So, which one is better? I can’t answer that, as I am no engineer, but the Cummins Two-Stage system seems simpler in my mind, though it is likely significantly bulkier than VGT. Time will undoubtedly answer the question of which system buyers prefer.