Check this out. BMW worked with BorgWarner to create what they consider the ultimate boosting system. How can we say that, because this engine is not only in one of their production vehicles, but it is in fact, in their M series (M550d).

If you don’t know, the M series BMW’s are considered the top end performance oriented vehicles. These are generally in extremely high demand because the performance is fantastic. It would be like a Shelby Mustang. Better than a standard Mustang GT and more performance than a SVT (if they still had them).

So, what is the engine?

Well, it is a 3.0L inline 6 producing 381 horsepower and 546 ft-lbs of torque. If you look at the torque and horsepower graphs, you will see that they both flat line. The torque flat lines between 2,000 and 3,000 rpms and the horsepower flat lines between 4,000 and 4,400. Have you ever seen a dyno sheet when the horsepower flat lines? Crazy right!

Ok, back to the three stage turbochargers. Unlike what you traditionally see in a triple turbocharger setup, where you have two atmosphere chargers and one high pressure charger (which is really a compound setup [2 stage] running parallel atmosphere chargers), this is actually considered three stages. The charger all the way in the back, the smallest of all three is a VTG (variable turbine geometry commonly called a VGT). Basically, as soon as the accelerator pedal is applied, the nozzles close and the small charger gets on boost. Then as the rpm picks up, the low pressure charger starts to kick in. Finally, as the rpm increases up into the upper range, the third charger kicks in. This is an odd charger because it is almost like a parallel high pressure charger because is basically receiving exhaust from the same source as the initial stage and then it exits the exhaust into the same hot pipe that feeds the atmosphere.

On a traditional triple stage, the smallest of stages receives the initial air from the exhaust manifolds, uses what energy it can and then sends it to the second stage and finally to the third stage or atmosphere charger. On the air side, it works backwards. So the atmosphere would receive the initial atmospheric air and pressurize it up. It would then feed the middle unit the boosted air; which would get pressurized even more until finally the smallest charger would be feed everything. The BMW system is quite different and unique.

While this engine is only offered in Europe, it is interesting to see what is going on at the OEM level. If companies are starting to experiment with this type of technology, could we one day see some of it in our larger engines here in the states?

Ford has tried a factory sequential system on the 6.4 liter and now is in production with a single sequential turbocharger. Could we see a larger atmosphere charger on feeding the Garrett single sequential?

Cummins and Duramax seem hesitant to play around with different combinations but who really knows what the next evolution will hold at this time. As the manufacturers try and squeeze out more performance through these emission regulated engines, they are surely experimenting with a wide range of ideals.