Critical Boosting: Testing Out Borg Warner’s S372 Turbocharger

If you’ve been interested in diesel performance for at least 5 minutes, you know that upgrading turbochargers are the primary modification for expanding your power potential. With hundreds of turbo selections on the market ranging from modified stock units such as the Fleece Cheetah all the way to monster, ball-bearing Garrett chargers, the possibilities are endless.

Turbo sizing can be an interesting topic and confusing to some. The turbos DNA can be read via a set of three numbers. For example, a 62/68/.80 would be a 62-MM compressor, 68-MM turbine, and a .80 A/R (aspect ratio) for the turbine housing. The A/R is a numerical ratio of the distance between the center of the turbine wheel to the OD of the housing as well as its overall volume. Sizing your turbos correctly will result in better performance and drivability. When sizing your turbo the saying “bigger is always better” couldn’t be further from the truth.

Shown is our test mule. This is a 2002 Ram 2500 with the 24-valve Cummins engine and the NV5600 six-speed transmission.

With the help of my friends at Diesel Auto Power, I have managed to make 541 horsepower and 1,032 lb-ft of torque so far. This combination consisted of their 7x.010, 150-horsepower injectors and a gated S300 63/68/.80. The guys at DAP reached out about testing a new S372 and I was on board from the start. DAP’s owner, Jacob Kidd, saw real potential in this charger and its T4, .83 turbine housing.

“This new .83 turbine housing outflows both the .91 and the 1.00 S300 housings because of the internal wastegate. This allows end-users to control shaft speed and prevent premature turbo failure,” said Kidd.

Making the switch from a T3 turbo to a T4 required an exhaust manifold change. DAP hooked us up with a three-piece, T4 manifold for this new turbo.

With the turbo and manifold situation complete, we upgraded tuning software as well. On the 24-valve trucks, Quadzilla Power and their 4K adrenaline offer endless adjustability to make the truck run better than ever. These boxes allow the engine to rev farther than 4,000-RPM and extend that power range out. With this in mind, and to lower crank vibrations down at high RPM, we also installed a Fluidampr harmonic balancer.  Upgraded valve springs and pushrods are also recommended for operation above 3500rpm.

On the left is the old 63-mm turbo and on the right is the new 72-mm. Look at the difference!

Not only is the turbo going to be larger and make more power, after a little elbow grease, it looks better too.  From the picture, you can also see that there is a significant size difference between the 63-MM(left) and the 72-MM(right).

It is also important to note that we needed to upgrade our injector to a 7.x012 keeping in mind the fueling restrictions of our high output vp44 we are limited in the injector category until the vp44 gets upgraded.  Too large of an injector will simply drain the injection pump of all of its fuel and causes air locking and stalling issues with no gains in power.

With the exhaust manifold studs in the head, the manifold install was done in a few minutes. To make the turbo install easier, we split the charger into three pieces; Exhaust housing, center cartridge, and the compressor housing. This makes it easy to reach the mounting hardware.

Unfortunately, the drain line I was using, wasn’t allowing the center section mate into the turbine housing. Instead of removing the drain line, we exchanged the housing out for a better-fitting .91 A/R one. This .91 housing still offered sufficient spool up and a good bit of flow over other options.

After dealing with these changes, the charger was on and ready for testing. With the help of the timing reduction feature, the Quadzilla has to offer, our turbo lights as fast as we want it. I can physically hear timing clatter dissipate as the RPM climbs and the boost starts to build.

With the turbo mounted, it’s nearly testing time.

In testing, I discovered this 372 would begin making boost at around 1,700-1,800 RPM. With a snap of the throttle, 50-PSI of boost very easy to reach. We are currently exploring options for waste gating because 50-PSI of boost is a tad too much.  45-PSI is a little better for the turbo longevity.

The s372 is a bit lazier in spool up compared to my old s363.  If we consider that we not only jumped up in turbine size and exhaust housing but also went from one of the smallest Borg-Warner s300’s to the biggest the slight lag in the spool is understandable.

Unlike before, this new Quadzilla tuning fuels harder to help spool the turbo, but doesn’t black the road out in the process.  This meant I could lean on the throttle more to aid in spooling the turbo without risk of smoke.  This is due to the far superior adjustability of the Quadzilla which ultimately aids in the driving experience.

The turbo and new manifold look right at home under the hood with the already powder coated valve cover and piping!

With the current fueling setup, I believe the truck should make 600-horsepower.  I have plans to install nitrous in the future as well as p pumping the engine to raise the power threshold.  The end goal is to reach 800hp and with this turbo, that goal should be easily reached.

If you’re looking for a turbo that performs well on the street and has a large power threshold then the s372 is your turbo.  For more information on this turbocharger, make sure to check out the Borg-Warner Website.  Make sure to visit my good friend at Diesel Auto Power, Quadzilla Power, and Fluidampr for all your high-performance diesel needs! We’ll see ya’ on the next one, and in the meantime, for more info on all that is going on in the world of diesel stay tuned to Diesel Army.

About the author

Keaton Samples

Keaton grew up messing with diesel trucks, in fact, his dad owns a diesel shop, which is where Keaton is currently employed since the age of 14. I fell in love with midsized diesel trucks around the age of 15-16 and eventually bought my own.
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