6.7 Cummins vs 6.6 Duramax

RCMAN46 wrote:
"They also operate at lower engine rpms, which lowers the piston speed. Pretty much an irrelevant negative on the I-6!"

If you are comparing the Cummins with the Duramax then you are dead wrong.


Here are the facts.

The Cummins makes its peak torque at 1800 rpm
The Duramax makes its peak torque at 1600 rpm

The Cummins makes its max horsepower at 2800 rpm.
The Duramax makes its max horsepower at 2800 rpm.

So much for the popular belief that the I6 Cummins operates at a lower rpm than the v8 Duramax.

So the statement that the Cummins operates at a higher piston speed holds true when comparing to the Duramax.

While I have been trying to stay away from this thread, there is more to this than peak torque/horsepower at wide open throttle where hardly any one drives at. The RPM peak torque is achieved at wide open throttle is mainly dictated by electronically controlled VG turbos anyways. However, under normal driving conditions there is what I refer to as natural torque and boost assisted torque and makes a bug difference in how the truck drives when not at wide open throttle.

Due to the longer stroke of the Cummins, it makes more natural low end torque without the assistance of the turbo. This is why people always say a Cummins pulls like a train because it generates so much torque at low revs under normal driving conditions. This is also why Pickuptrucks.com and a few of the other review sites have said that the Cummins feels least phased by loads compared to the other two under normal driving conditions especially under 1,600 rpm.

The short stroke Duramax on the other hand utilizes the turbo more to achieve its torque at low rpm under normal driving conditions. Giver here the throttle and it will blow the doors off of the Ram, but it feels likes it has less torque under 1,600 rpm versus the Cummins in normal driving conditions until the turbos are spooled. When I was driving my cousins L5P, you did not get the same torque pull feel until higher rpms as you did on my truck at just 1,400 rpm.

Not trying to dis the Duramax because it is a great engine and is very quick at wide open throttle in stock form versus the other two if that is what you are after, but it does feel like it has less torque at low rpms in normal driving conditions versus the Cummins regardless of when it's turbo is programmed to achieve peak torque at wide open throttle. Drive and tow with both back to back and you will see what mean. My brother even says the same about his old 2012 PSD versus his current 2014 CTD and my father in law with his 2018 PSD versus my CTD.