duramax vs cummins
July 6, 2020

Duramax vs. Cummins

Written By: ProSource Diesel

Which Diesel Engine Should You Choose?

Two of the top names in the American diesel truck industry are Duramax and Cummins. You’ll find Duramax diesel engines across the General Motors line, including Chevy. Cummins diesel engines are primarily in the Ram truck line which is owned by Fiat Chrysler, but you’ll also find them in the Nissan Titan line of trucks. Which engine should you choose? This may sound like an oversimplified answer but it largely depends on what you want. One engine is not necessarily better than the other. Duramax and Cummins engines have differences and similarities. Let’s take a look at what makes them tick.

History and Time on The Market


The Cummins engine has over 100 years of history, which is quite a bit longer than the Duramax. The engine got its start back in 1919. Chrysler Corporation began putting Cummins engines in its Ram trucks in 1989. On the other hand, GM’s Duramax got started barely 20 years ago in 2001. If you’re looking for a diesel engine with a long history, then Cummins fits the bill.

The first Cummins diesel in Ram trucks was the 5.9-liter six-cylinder turbodiesel that put out 400 pound-feet of torque. Even though both Ford and Chevy had diesel engines at this time, the Cummins diesel revolutionized the market by offering a turbocharger, direct injection and 400 lb-ft of torque; things Ford and Chevy did not offer.

In 2007, the 6.7-liter replaced the 5.9-liter Cummins diesel. Although many 6.7 Cummins parts were similar to the 5.9 Cummins parts, the new engine was designed to meet changing emissions standards. It offered as much as 650 pound-feet of torque while also being fifty percent quieter.


The Duramax engine got started with a partnership between General Motors and Isuzu. The first generation of Duramax came out in 2001 and offered 520 pound-feet of torque. New LB7 Duramax parts included a high-pressure, common-rail Bosch CP3 injection pump, which was something that the Cummins engine didn’t start using until 2003.

The Duramax has seen several updates since its initial release. The Duramax LLY and LBZ engines came out in 2004 and 2006 respectively. The Duramax LMM came out in mid-2007 and the LML came out in 2011. The latter engine lasted until 2016 when the Duramax L5P replaced it to add more power.

Torque Production

Many people buy diesel trucks to tow heavy items like boats, horse trailers, campers, and heavy equipment. To do this, you need torque – and a lot of it! Diesel engines have the ability to produce torque on a much higher level than gas engines. How much torque is produced by Duramax or Cummins diesel engines varies greatly from engine to engine and truck to truck.

For example, a 2018 GMC Sierra HD with a Duramax 6.6-liter diesel produces 910 pound-feet of torque. The Nissan Titan XD with a Cummins 5.0-liter diesel makes 555 pound-feet of torque, and the Cummins 6.7-liter diesel in a 2018 Ram Heavy Duty truck makes 930 pound-feet of torque.

Between 2001 and 2004, the Duramax 6.6L LB7 produced a segment-leading 520 pound-feet of torque. But by mid-2007, the 5.9-liter Cummins output a total of 610 pound-feet of torque while the Duramax 6.6L LMM put out 650 pound-feet of torque. Since then, both engines have maintained similar specs once their history began to intersect.


Even though torque ranks highest in importance for towing, horsepower isn’t far behind. More horsepower means faster acceleration whether you’re towing or not. The current Duramax 6.6L L5P diesel wins this category with 445 horsepower. The current 6.7L 24V Ram Cummins diesel engines produce 400 horsepower. Historically, horsepower has swayed slightly in favor of the Duramax versus the Cummins line.

Cummins Vs. Duramax Specs

The current Cummins engine is a 6.7-liter inline-six, while the Duramax is a 6.6-liter V8. The Duramax leads with horsepower, but the Cummins is the king of torque with numbers up to 1,000 ft-lbs depending on the truck. Let’s take a look at some other specs.

· Displacement

  • 6.7-liter Cummins Diesel I6: 408 cubic inches
  • 6.6-liter Duramax L5P V8: 403 cubic inches

· Valvetrain

  • 6.7-liter Cummins Diesel I6: OHV – 24 valves, 4 per cylinder, solid lifter camshaft
  • 6.6-liter Duramax L5P V8: OHV – 32 valves, 4 per cylinder, mechanical roller lifters

· Bore x Stroke

  • 6.7-liter Cummins Diesel I6: 4.21 x 4.88 inches
  • 6.6-liter Duramax L5P V8: 4.055 x 3.897 inches

· Firing Order

  • 6.7-liter Cummins Diesel I6: 1-5-3-6-2-4
  • 6.6-liter Duramax L5P V8: 1-2-7-8-4-5-6-3

· Compression Ratio

  • 6.7-liter Cummins Diesel I6: 16.2:1
  • 6.6-liter Duramax L5P V8: 16.0:1

· Fuel and Fuel System

  • Both engines use ultra-low sulfur diesel and B20 biodiesel as well as direct injection with high-pressure common rail.

· Engine Block

  • 6.7-liter Cummins Diesel I6: Compacted graphite iron
  • 6.6-liter Duramax L5P V8: Cast Iron

· Cylinder Heads

  • 6.7-liter Cummins Diesel I6: Cast Iron
  • 6.6-liter Duramax L5P V8: Cast Aluminum


There’s no doubt that Cummins engines can generally tow the most. However, towing over 26,000 pounds in America requires a CDL (Commercial Driver’s License). Besides, most passenger and light work trucks don’t need to tow that much. Both modern Cummins and Duramax engines are quite capable of towing what the average truck driver needs. Picking one engine over the other largely depends on your preference for the trucks they’re in.

Whatever engine you choose, remember to use ProSource for all your diesel truck parts needs, including Dodge diesel parts and GM Duramax parts.

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1 Comment

  1. Chuck Sweet on May 22, 2021 at 10:46 AM

    Thank you for the info- well presented

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