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Cummins Twin Turbos

Posted on 13 June 2015

I was asked this question a few times this week - "What kind of twin turbos do you sell for a Cummins?"  I had a great conversation with the customer and ended up shipping him an ATS Aurora 7500 kit for his 2008 6.7L Cummins.  During this conversation, I realized that "compound" and "twin" turbo systems aren't always understood.

A twin turbo setup is common on performance gas applications.  It involves two equally sized turbos feeding air into a motor.  For example, two S475 Borg Warner turbos on a Camaro or Mustang.  In the diesel world, while two turbos are involved, they are not equal size.  Let's take the Aurora 7500 Compound Kit - it utilizes the stock VGT (approximately 60mm in compressor size) and adds an 80mm T6 above it.  The result are two different sized turbos, and this is by design.

The small turbo in a compound arrangement provides the quick spooling characteristics.  Another way to put it is that the drivability on the street comes from this small turbo.  When first accelerating, it builds boost and starts to feed the large turbo (in this example the ATS 7500).  As boost rises, it begins to drive the 7500 faster and this big charger produces more airflow.  This is where the EGT control and top-end performance comes from.

Mixing and matching small and big turbos can provide different benefits and drawbacks.  A race compound setup isn't focused on low-end performance for towing - it doesn't need to.  It needs to flow massive amounts of air at full throttle going down the track.  On the contrary, a tow setup doesn't need 80-90 PSI to clean up 200% over injectors to pull a tow hauler.  

Manufacturers, like ATS, size their compound setups for specific uses, be it towing, daily driving, racing or a little bit of everything.  Street Diesel Power can help you select the right compound turbo setup for your 5.9L or 6.7L Cummins. Give us a call, send us an email or chat into our site and we will answer your compound turbo questions!

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