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A close up shows a red 2022 Ram 2500 at a Ram 2500 dealership.

Getting to Know the Big Three Diesel Engines: Cummins, Duramax, and PowerStroke

Ask any mechanic at your local Ram 2500 dealership or service center to choose between a Cummins diesel or a gas-powered engine for a heavy-duty truck, and they’ll always choose the Cummins. Why? Diesel engines are notorious for their capability, efficiency, and longevity. Long-time Dodge and Ram fans will tell you, “Nothing beats a Cummins.”

What makes the Cummins so special? The average life of a Cummins diesel engine ranges anywhere from 350,000 to 500,000 miles. You’ll likely trade in your Ram truck long before you break in the engine, which says a lot about the Cummins and its reliability. What else makes the Cummins remarkable, and how does it compare to other diesel powertrains like Ford’s Power Stroke or GM’s Duramax? It’s time to find out.

The Makings of a Diesel: How It Operates

Invented in the late 19th century by a German thermal engineer named Rudolf Diesel, diesel engines were originally used in ships and trains before the automotive industry discovered their capability. As gas prices soared in the 1970s, diesel engines became even more attractive and found a coveted place in the American automotive industry. After five decades, that hasn’t changed. So, how do they work?

Both gas and diesel engines use internal combustion, which is when air enters the engine and mixes with fuel to create a series of explosions. However, while the basic principles are the same, there are some major differences between gas and diesel. On a gas-powered engine, a spark plug ignites the fuel and air to start a chain of events that propels the vehicle forward. Diesel engines approach the process differently.

Diesel engines use a four-stroke combustion cycle that starts with the intake valve opening to let the air in while the piston moves down. The piston then moves up again to compress the air. As the piston reaches the top, fuel is injected and ignited. This explosion forces the piston back down and then up again to push the exhaust out of the exhaust valve. Unlike a gas engine, though, there is no spark plug – ignition is purely the result of compression.

A 2022 Ram 2500 Cummins engine is shown on a black background.

Why Compression Matters

As Diesel designed the first internal combustion engine, he discovered the importance of compression. He theorized that an engine with higher compression delivered more power and greater efficiency. The diesel engine proved his theory. When the piston compresses the fuel-air mix in the cylinder, the mix becomes extremely concentrated. The more concentrated that it becomes, the greater the usable energy when it is ignited.

However, extreme compression has a secondary effect of heating whatever is being compressed. Compress it enough, and it will spontaneously ignite without needing a spark plug. In a gasoline engine, this is called “pre-ignition” and can damage the engine, but diesel engines are designed for it, reducing the complexity of the engine.

Cummins, Duramax, and Power Stroke: What’s the Difference?

If diesel engines all work the same way and they all have relatively long lifespans of up to 500,000 miles, what makes the Cummins different from GM’s Duramax or Ford’s Power Stroke? The best way to answer that is to compare the 2021 engines: the standard and high output 6.7-liter Cummins turbo-diesel I-6, the 6.6-liter Duramax turbo-diesel V8, and the 6.7-liter Power Stroke diesel V8.

  • Cylinder Layout: The Cummins turbo-diesel is an inline six-cylinder engine, which means the cylinders are aligned rather than in a V-pattern like the Power Stroke V8 and the Duramax V8. This results in a smoother and longer-lasting engine.
  • Displacement: The Cummins and the Power Stroke offer the same displacement of 6.7-liters, with the Duramax in close proximity at 6.6 liters.
  • Horsepower: The standard and high output Cummins engines deliver 370 horsepower and 420 horsepower, respectively, at 2,800 rpm. The Duramax delivers 445 horsepower at 2,800 rpm, and the Power Stroke delivers 475 horsepower at 2,600 rpm.
  • Torque: The standard output Cummins delivers 850 lb-ft at 1,700 rpm, and the high output Cummins delivers 1,075 lb-ft at 1,800 rpm. The Duramax and Power Stroke both reach their peak torque at 1,600 rpm, with the Duramax at 910 lb-ft and the Power Stroke at 1,050 lb-ft.
  • Transmission: The Cummins is mated to a 6-speed automatic transmission while the Duramax and Power Stroke are mated to 10-speed automatic transmissions.
  • While these categories show the differences between the Cummins, Duramax, and Power Stroke engines, they also reveal just how slight those differences are. For example, heavy-duty trucks are renowned for their ability to tow heavy loads, which is where torque plays a prominent role. While having a lot of torque is ideal, it’s also important to look at when that torque is delivered or, in other words, the rpms.

Let’s say that you’re towing a camper out of town for the weekend. Just before you leave the city limits, you’re stopped at a traffic light. When your diesel engine delivers higher torque at a lower rpm, it means you don’t have to rev the engine to get the power you need. This means you can accelerate from a stop quickly since the engine gives you the power you need to accelerate and pull the load.

Now, let’s say that you’ve made it out of town with the camper and your route includes a few miles of mountainous highways. Your diesel engine with its higher torque at a lower rpm is ideal for quickly accelerating from a standstill, but what happens if your engine works the opposite and delivers its peak torque at a higher rpm? In this case, your engine gives you more power when you’re already underway. So, while the truck may be sluggish as it starts pulling its load up the hill, it gains more speed and capability as it reaches its max torque and rpm.

A blue 2022 Ram 2500 is shown towing a red tractor.

Adding Longevity to Your Diesel Engine

Whether your truck is equipped with a Cummins, Duramax, or Power Stroke, you can usually expect to get anywhere from 350,000 to 500,000 miles from the engine. In most cases, you’ll trade the truck long before the engine quits. However, it’s still important to maintain your diesel to optimize its performance and extend its lifespan.

Heavy-duty trucks like the Ram 2500 are designed as workhorses, and that means you can take them anywhere and push their towing and hauling limits. While diesel engines have fewer components than their gas-powered counterparts, they still require routine maintenance and cleaning, especially if you spend a lot of time on dirt roads or other harsh terrains or climates. Before you get started, check your owner’s manual for recommendations on how to care for the engine properly.

While you’re cleaning the engine, check and replace the air filter. Dirty air filters can bog down the engine making it weaker and adding unnecessary wear. You’ll also want to check and replace the fuel filters. Most diesel engines have a primary and a secondary filter, both of which see more use than in a gas engine due to the fact that diesel fuel is less refined.

What’s Under Your Hood?

Do you have a Cummins, Duramax, or Power Stroke under the hood of your truck? Regardless of which one powers your road warrior, you’re likely enjoying the benefits of everything a diesel engine has to offer. They’re reliable, durable, efficient, and wildly capable, all of which is why they’re the heartbeat of heavy-duty workhorses like the Ram 2500, Ford F-250, and Chevy Silverado 2500 HD.