The final piece to our high-mount compound turbocharger build has finally arrived! If you’ve been following along with what we’ve received so far, we’ve taken a look at a multitude of parts, including Exergy injectors and CP3 pump, a FASS high-lift fuel pump, an ARP 625+ head stud kit, a Pusher High-Mount Compound Turbo System, and Edge Products Insights Pro CTS2 and EAS Data Logging Kit.

In some ways, this turbocharger is the star of the show – not only will it give our Cummins dually the added boost and burliness we’re seeking, but it will also give the truck the kind of long-life service and reliability that’s so synonymous with diesel trucks. In our case, we opted for BorgWarner’s S400SX with a 71mm compressor wheel inducer and a 87mm turbine wheel (PN 171701).

The part number (171701) for our turbo applies to several different models. Ours has the 71mm compressor wheel inducer and a 87mm turbine wheel.

To get a better grasp on the turbocharger, we spoke with BorgWarner’s Brian Rhinehart. We learned that our S400SX packed some terrific features, one of them being the compressor cover recirculation groove.

“The compressor cover recirculation groove is also referred to as a map width enhancement groove,” said Rhinehart. “What it does is it moves the surge line to the left, increasing margin from the engine operating point to the shifted surge line.”

In 2013, BorgWarner revised the 171701 to have the logo included, as well as to improve performance.

Our S400SX has a recirculating groove (partially indicated by the concentric opening surrounding the compressor wheel). This groove allows the turbocharger to be more versatile and remain a solid platform to build on with modifications, like fueling and tuning.

Put another way, the groove allows the turbocharger to have a greater versatility without the worry that it will surge and start fighting itself. That way, it can work with a variety of applications (like our 24-valve 5.9-liter Cummins) and still operate effectively.

One neat feature of the S400SX is its extended tip technology, relating to the design of the compressor wheel. “The wheel is designed using computer programs that develop a three-dimensional calculation of airflow and pressure,” said BorgWarner’s Brian Rhinehart.

Another defining factor of the S400SX is its extended tip technology, and pertains to the compressor wheel’s design. “The design promotes greater airflow using a low-intertia wheel that performs like a wheel of greater size and mass,” said Rhinehart. “The technology enables users to have faster spool-up at lower engine speeds while providing boost for top-end performance, which is something most turbocharger enthusiasts desire.

With this knowledge in mind, we now feel better with the decision we made for our second turbo on our compound turbo build. Stay tuned as we get ready to start the installation, and be sure to check out more from BorgWarner on the company’s website. Also, if you’re eager to see what turbocharger would best suit your needs, be sure to visit the BorgWarner MatchBot.