Evolution of the Duramax

March 6, 2019

History of Duramax Engines

As with most pickups in the industry, the Duramax line of diesel engines has come a long way from its inception to modern day. From the introduction of the LB7 almost 20 years ago, the engine output has nearly doubled its torque from approx. 500 lb-ft, to the modern-day workhorse pushing towards 1000 lb-ft, in the L5P engine line.

Though all of the Marketing departments at the big three diesel manufacturers tout the best in trucks, Dan Zelten of Dan’s Service Center (Eagle River, WI) claims he sees the least amount of Chevy’s in the shop for engine repairs. “A lot of Ford’s, however, have provided a good amount of business for us.”

For GM, they set the trend, teaming with Japanese manufacturer Isuzu, making it to market with the first redesign of the current-style high pressure direct-injector diesel engines. Dodge Cummins and Ford Power Strokes soon followed to take advantage of the new common rail injection design.

The First Duramax Diesel

Prior to the release of the newly designed LB7, the Duramax was delivering 400+ lb-ft of torque. The revised 6.6L V-8 turbo diesel motor came along at the turn of the century featuring aluminum heads and 32 valves. With their high-pressure, common-rail, direct fuel injection mounted under the valve covers.

As the first attempt with the new injector design, one might imagine it had its bugs to squash. “GM tried it, and it was a great motor,” says Zelten. “But the injectors were not.” The remainder of the design however, was on track and began the ascent into better delivery of torque. The LB7 Duramax diesel delivered 235 hp @ 2700 RPM with 500 lb-ft of torque at 1600 RPM.

With the injectors as an issue, the next upgrades came along in 2004, with the new LLY completely replacing the LB7 by middle of the year. The redesign incorporated a revised valve design so the injectors had improved accessibility for repairs, in addition to a turbo redesign improving low-end response. A new exhaust design introduced the recirculation system into the GM motor providing a second burn of the carbons for improved emissions. “They added the VGT (variable-geometry turbo). It was a huge jump up for drivability,” says Dan. The cumulative revisions resulted in an improvement from the LB7 300 hp @ 3,100 rpm with 520 lb-ft @ 1,800 rpm, to the LLY delivering 310 hp @ 3,000 rpm with 520 lb-ft @ 1,600 rpm.

Improving the Duramax Engine

By 2006 GM had hit stride adding the six-speed Allison transmission. The Duramax LLY included additional improvements in torque, measuring approx. 605 lb-ft @ 1,600 rpm.

The LBZ design replaced the LLY by 2007 delivering 360 hp @ 3,200 rpm with 650 lb-ft @ 1,600 rpm. Dan says, “They enhanced a little bit more with an updated VGT turbo design, new piston design, and heads that could handle more pressure. That’s when they also began to choke them out with the emissions.” The redesign included improvements to the fuel system with higher-pressure levels through improved injector design. With improved fuel in, a larger EGR cooler setup was implemented to improve exhaust quality leaving the engine. Computerization was also introduced to improve power, efficiency, and emissions.

The LBZ was followed by the LMM, which was essentially the “same motor with more emissions,” says Zelten, “like the passive catalytic converter.” The LBZ added the diesel particulate filter (DPF) to capture up to 80% more soot. With the reduction of harmful particulates, the DPF side effects include reduced fuel economy, blockage within the DPF, and the risk of expensive repairs.

In 2011 the LML evolved next in the Duramax history, incorporating a total redesign. “They drastically beefed up the motor, cooling system, transmission and emissions,” says Zelten. The DMAX combination included new attention to the fuel allowing biodiesel as an option without risk to warranty. The fuel system itself incorporated new piezo-controlled injectors, an additional injector to help DPF regeneration, a cooler-bypass EGR system and a new SCR (selective catalytic reduction) system.

The LML also introduced the smart brake system to automatically begin slowing down a heavy-loaded vehicle without applying the brakes. By taking advantage of the downshifting through the gears, the RPMs increase in the motor providing more exhaust in the turbo, to therefore utilize an internal sliding nozzle to cause backpressure.

Zelten says, “The LML transmission design changed everything over to a control solenoid for better shifting and reduced slipping.” Dan also notes that the CP4 pumps could provide an expensive repair if not maintained properly.”

With the 2017 redesign from turbocharger to injectors, fuel pumps to cylinder heads, the present-day Duramax LP5 delivers approx. 445 hp @ 2,800 rpm with 910 lb-ft @ 1,600 rpm from a stock diesel. It also includes enhanced security in the computer preventing the elimination of emissions components.

Common Duramax Maintenance

When asked of any common maintenance required across the entire line of Duramax models, Zelten says, “Protect your investment. Make sure you are running a fuel additive, and change your oil. If hauling a lot, make sure to change your transmission fluid. Do the regularly needed simple stuff that is going to make these engines live and last.

Zelten also advises that while good information is available online, there is too much bad information online that overpowers accuracy. “Talk to an educated person with expertise in diesel,” says Dan. “Don’t fall for the BS posts and comments. Some of the information I read is shocking. With proper knowledge and diagnosis, these trucks are fairly simple to work on. But work with an expert for both advice and repairs. Don’t guess – take it to a shop. You’ll pay far less in the long run.”

Whether stock or modified, for those interested in more towing capabilities and pushing or pulling a heavier load, the diesel truck, regardless of manufacturer,” says Zelten, “is going to be a more reliable vehicle delivering far better gas mileage with less engine and transmission strain.”

“You can’t beat the Allison transmission behind the Duramax. Hook 12,000 lbs. to a gas truck and the driver’s foot is most of the way in it,” says Zelten, “hook on to a diesel and the truck doesn’t even downshift out of overdrive.”


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Dan Zelten of Dan’s Service Center, Eagle River, WI