6.6 Duramax Vs. 6.7 Power Stroke: How Do These Diesel Engines Compare?

Of the three United States automakers that offer diesel-powered heavy-duty pickup trucks, only two of those diesel engines are V8s. Those V8 diesel engines are the 6.6 Duramax found in offerings from General Motors, and Ford's 6.7 Power Stroke. As you probably know, General Motors (GM) produces two distinct lines of full-size pickup trucks, the GMC Sierra and Chevrolet Silverado. Both brands designate their heavy-duty models as 2500 and 3500, and it's within that range you'll find options for the 6.6-liter Duramax diesel engine.

Like GM, Ford only provides its powerful diesel engine option, the 6.7-liter Power Stroke, for its heavy-duty pickups, such as the F-250, F-350, and F-450 Super Duty models. Of course, both automakers equip their larger chassis-cab trucks with diesel power as well.

The two diesel engines have powered their respective brands' pickups admirably for some time now. The 6.6 Duramax is the senior of the two, debuting for the 2001 model year. According to MotorTrend, it was the first U.S. market diesel engine to use a "high-pressure common-rail, direct-injection" fuel system. It took Ford over two years to implement its own high-pressure fuel-injection system on the 6.0-liter Power Stroke, and the Blue Oval brand didn't come out with the 6.7 Power Stroke until 2011.

In addition to its groundbreaking fuel injection system, the first iteration of the 6.6L Duramax diesel engine, the LB7, featured 300 horsepower and 520 lb-ft of torque. It was replaced by the 310-hp LLY Duramax, with 605 lb-ft of torque, halfway through the 2004 model year. More changes with increased power came on a regular basis, with the LBZ in 2006, the LML in 2011, and the L5P in 2017, with 445 horsepower and 910 lb-ft of torque, being among the most notable versions.

Chevrolet advertises 470 horsepower and 975 lb-ft of torque for the enhanced L5P 6.6 Duramax available in the 2025 Silverado HD pickup. The drivetrain includes a 10-speed Allison automatic transmission and provides up to 36,000 pounds of towing capacity when properly equipped. The Duramax is built on a strong foundation with its cast iron engine block, cast aluminum cylinder heads, and forged steel crankshaft.

Ford's 6.7 Power Stroke diesel engine has evolved over three generations, spanning 15 model years to date. The first generation, often considered some of the worst years for the 6.7 Power Stroke, produced 390 horsepower and 735 lb-ft of torque. Not only are the third-gen 6.7 Power Stroke diesel engines more reliable than the first-gen engines, but they're also more powerful. However, the second-generation 6.7 Power Stroke, produced from 2015 through 2019, is also reliable, although it can't match the power of the new 6.7 Power Stroke.

The newest Ford Super Duty pickup trucks offer a choice between standard output and high output 6.7L Power Stroke versions. The standard output third-gen 6.7 Power Stroke generates 475 horsepower and 1,050 lb-ft of torque. While those impressive numbers top those of the 6.6 Duramax, the high output 6.7 Power Stroke raises the bar with 500 horsepower and 1,200 lb-ft of torque. Either diesel engine option for the Ford F-350 Super Duty comes with a 10-speed automatic transmission and provides up to a maximum of 40,000 pounds of towing. Like the 6.6 Duramax, the 6.7 Power Stroke uses aluminum cylinder heads. However, the Ford engine uses an engine block made from compacted graphite iron (CGI).