Best Duramax Engines

There are a few details that all Duramax V-8 engines from LB7 to L5P share in common, and it begins with displacement. The Duramax V-8 displaces 6,599 cubic centimeters, which is equivalent to 6.6-liters or 402.7 cubic inches. Cylinder bore is 4.06 inches (103 mm) and piston stroke is 3.90 inches (90 mm). The engine’s base design is that of a 90-degree V. Engine blocks are cast of iron and heads are aluminum. To reduce wear, the upper portion of each cylinder bore is induction hardened. Pistons are constructed of a high-silicon aluminum alloy and rods utilize a fractured cap. The oil capacity of the 6.6-liter Duramax is 10 quarts (9.2 without the filter).

First Generation – LB7: 2001 to 2004.5

The first Duramax engine, coded LB7, made its debut for model year 2001. This engine would lay the groundwork for decades to come. A single fixed-geometry IHI turbocharger resides at the rear of the engine’s lifter valley. High-pressure fuel is delivered to the injectors by way of a Bosch CP3 injection pump. The fuel injectors are housed under the valve covers. The LB7 has a compression ratio of 17.5:1 and produces 300 horsepower at 3,100 rpm and 520 lb-ft of torque at 1,800.

Two versions of the engine existed in the wild: one with Federal emissions and the other with California emissions. Federal emissions LB7s were the more desirable of the two, as they lacked any performance-zapping hardware. California-certified engines were equipped with a passive catalyst, cooled exhaust gas recirculation, different heads, and a unique turbocharger housing. 

LB7s had an issue with leaking fuel injectors, which led to GM extending the warranty on the units to 200,000 miles. Because of the injectors being housed under the valve covers, diesel fuel was allowed to leak into the crankcase, causing dilution. The injectors were subsequently redesigned to correct the issue.

All LB7 engines were backed with a ZF-sourced six-speed manual transmission standard, with a five-speed Allison automatic being an often-selected option. Trucks with LB7 engines are identified by engine code “1” in the eighth position of the Vehicle Identification Number (VIN).

Second Generation – LLY: 2004.5 to 2005

Building on the success of the LB7, changes to the second-generation LLY Duramax engine revolved mostly around emissions equipment. Cooled exhaust gas recirculation was now standard on all engines, as was a catalytic converter. Improving emissions and power, a new variable geometry turbocharger from Garrett replaced the LB7’s IHI unit. Electronically controlled movable vanes in the turbine housing allowed the turbocharger to dynamically change the volume of air on its exhaust side. Low-end response improved and power output increased to 310 horsepower at 3,000 rpm and 605 lb-ft of torque at 1,500.

Other subtle changes occurred as well, such as a redesign of the valve covers. Doing so made the fuel injectors accessible without removing the valve cover, which greatly reduced repair time over the LB7.

Because it was a mid-year change, identifying 2004 model-year trucks with the LLY can be tricky. It’s best to consult the VIN and look for engine code “2” in the eighth position. Intestinally, along with 2004.5 and 2005 Chevrolet Silverados and GMC Sierra pickups, the LLY Duramax was also in the Hummer H1 Alpha, along with the medium-duty Chevrolet Kodiak and GMC Topkick. Power output for these vehicles was rated at only 300 horsepower and 520 lb-ft of torque, same as the previous-generation LB7. 

A further de-tuned version, making 250 horsepower and 460 lb-ft of torque, was used in the 2006 Chevrolet Express and GMC Savana full-size vans as well. The lower power figures were needed to prolong the life of the van’s four-speed Hydra-Matic 4L80E automatic transmission.

Third Generation – LBZ: 2006 to 2007.5

The game changed yet again with the introduction of the LBZ Duramax for the 2006 model year. Not since the very first LB7 had the Duramax engine gone through such a vast set of changes and improvements. First, the block casting and machining improved slightly in order to strengthen the bottom of the cylinder bores to better handle the increased power. Main bearing material was upgraded for better durability. Compression ratio was lowered from 17.5:1 to 16.8:1 by way of a new piston design, and the rod pin bore diameter was increased. Connecting rods were given a larger section width, and the heads were revised.

Improvements to the fuel delivery system were implemented as well, with the adoption of a new injector design with seven-hole nozzles. Injection pressure was increased from 23,000 psi to more than 26,000 psi. High-pressure fuel rails and delivery lines were also revised, as was the glow plug system. A new version of Garrett’s variable geometry turbocharger was put into service, and the air induction system was retuned for better acoustic control.

The LBZ saw the first use of GM’s new E35 32-bit engine controller as well. EGR was still present, though now with a larger cooler, as was the passive catalytic converter.

It’s worth noting that the LBZ was the last generation of Duramax to not come equipped with a diesel particulate filter as part of the exhaust system. This, combined with the improvements over the LLY, makes it an incredibly desirable platform for the performance-minded enthusiast. LBZ-equipped trucks can be verified by looking for engine code “D” in the eighth VIN position.

With the job of transferring power to the wheels, the Allison 1000 automatic transmission gained a cog, increasing from five forward gears to six. This generation also saw the demise of the ZF six-speed manual, which had become optional.

Power output increased to 360 horsepower at 3,200 rpm, and torque rose to 650 lb-ft at 1,600. Kodiak and Topkick saw a bump as well, remaining at 300 horsepower but increasing torque to 605 lb-ft.

Fourth Generation – LMM: 2007.5 to 2010

Introduced mid-year in 2007, the LMM made its first appearance in GM’s new GMT-900 platform pickup, which was a ground-up redesign. Again it was tightening emissions regulations that forced most of the updates to this generation. The exhaust gas recirculation system was again improved and upsized, as was the catalytic converter. To reduce NOx emissions, the crankcase ventilation system went from an open to closed loop. New low-ash engine oil, meeting the CJ-4 standard, was made a requirement. Cooling system capacity was increased. And largest of all was the addition of a diesel particulate filter (DPF).

In the grand scheme, the ultimate goal with diesel emissions was to reduce NOx output. However, NOx and particulate generation go hand-in-hand. The answer then was to run lower in-cylinder temperatures, which produces less NOx but great amounts of particulate, and capture the particulate on the way out. Solid theory, however, when the particulate filter becomes clogged the only way to remove the matter is to burn it out. This is done by injecting raw fuel into the exhaust stream in an effort to raise exhaust temperatures high enough to burn off the particulate and clear the filter. While the system works, fuel economy suffers greatly during the active regeneration event.

Despite ever-tightening emissions regulations, power output was again raised. Chevrolet and GMC pickups received a modest bump to 365 horsepower at 3,200 rpm and 660 lb-ft at 1,600. Kodiak and Topkick also received an increase with the LMM, which was known by RPO code LYE or LRX in the medium-duty trucks. These now made 330 horsepower and 620 lb-ft of torque.

In the Express and Savana vans, the LMM Duramax was present in some form from 2007 until 2016. From 2007-2010 power was rated at 250 horsepower and 460 lb-ft of torque. Power was increased for 2011-2016 models to 260 horsepower and 525 lb-ft, and the engine’s RPO code changed to LGH. The transmission was also upgraded to a Hydra-Matic 6L90 six-speed automatic.  

To identify an LMM-equipped vehicle, look for engine code “6” at the eighth place of the VIN.

Fifth Generation – LML: 2011 to 2016

Once again pushed forward by constricting emissions standards, the fifth-generation LML Duramax saw the largest amount of change since the LBZ. The LML saw a major update to the fuel injection system with the switch to piezo-controlled injectors and a new Bosch CP4.2 high-pressure injection pump. These new injectors were capable of multiple injection events per cycle, including pre- and post-combustion, and a ninth injector was added downstream in the exhaust tract to aid in particulate filter regeneration. Injection pressure was raised again, this time to 29,000 psi. This ability helped improve both emission and engine noise and vibration. The entire fuel system, from tank to injectors, was also revised with the ability to run on a blend of up to 20 percent bio diesel.

Inside the engine, piston oil flow was improved for better lubrication and cooling, and a new oil pump was added to support this. The engine’s Garrett variable geometry turbocharger was again upgraded, and the ability for the adjustable vanes to act as an on-demand user-selectable exhaust brake was added.

The most important update, again, was found in the exhaust system. To better scrub the exhaust of harmful NOx emissions, a Selective Catalyst Reduction system utilizing urea was implemented. By adding ultra refined urea, known as diesel exhaust fluid (DEF), to the exhaust stream and then passing it through a catalyst, virtually all NOx emissions can be scrubbed. Doing this also allows for in-cylinder temperatures to be hotter, thereby creating less particulate and leading to fewer regeneration cycles. The net benefit, other than cleaner exhaust emissions, is a stark improvement in fuel economy over the previous DPF-only generation.

Because the engine was again allowed to run more efficiently, power levels increased by the largest margin up to this point. The LML was found only in Silverado and Sierra pickups, and produced 397 horsepower at 3,000 rpm and 765 lb-ft of torque. The medium-duty Kodiak and Topkick had gone out of production by this point. LML was the longest running single generation of Duramax engine, and is denoted by engine code “8” in the vehicle identification number.

Sixth Generation – L5P: 2017 to Current

The sixth-generation L5P Duramax is the most extreme refresh since the first LB7 rolled off the line, sharing little more than bore and stroke dimensions with its predecessors. Starting at the core, the L5P’s block is 20 percent stronger than the outgoing LML, and is nine pounds heavier. Pistons are taller and feature a larger wrist pin, along with having laser melted tops and radiused bowl lips. Connecting rods see a 20 percent increase in strength, along with featuring an offset bearing cap. The engine’s oil pump has 19.6 percent more capacity and is capable of flowing 21 gallons-per-minute.

Injectors are no longer Bosch units, rather Denso’s G4S Gen-III solenoid-type with Mini-Sac nozzles. The high-pressure injection pump also changes from a Bosch unit to a Denso HP4. LS-style valve lifters shave 64 grams off of the previous unit, and pushrods cut another 1.3 grams apiece, despite being thicker than previously. Valve size remains the same in the heads, however the L5P’s exhaust ports are noticeably larger. Crank and rod bearings all increase in width along with the crankshaft being an all-new design.

The turbocharger changes from the standby Garret unit to a BorgWarner piece. This new turbo features a billet compressor wheel, electronically actuated wastegate, and an exhaust-housing-mounted catalyst. Producing 470 hp and 975 lb-ft of torque, the L5P is the strongest Duramax yet.

The “Other” Duramax Engines

As any good organization would, General Motors has utilized the success of the 6.6-liter Duramax diesel engine to spin up the marketing machine in favor of more compression-ignition mills. While some of these engines carry the Duramax name, they may not necessarily have been produced by the DMAX Ltd. joint venture.

LM2/LZ0 – 3.0-liter

The LM2 “baby Duramax” 3.0-liter I-6, produced at the Flint Engine Operations Plant, made 277 horsepower and 460 lb-ft of torque. It was fitted in light-duty trucks and SUVs, including the Silverado 1500/Sierra 1500, Tahoe/Yukon, Suburban/Yukon XL, and Escalade. The ½-ton trucks got this diesel for late-model 2019, at that time competing with Ram’s 3.0-liter V-6 EcoDiesel and Ford’s 3.0-liter V-6 Power Stroke. The second-generation LZ0 followed for model-year 2023, bumping horsepower to 305 and lb-ft of torque to 495. The bumps came courtesy of a re-tuned turbo compressor; new, higher-flow fuel injectors; revised piston-cooling oil jets; new steel pistons;  and more. The SUVs got the LM2 for model-year 2021 and get upgraded to the LZO for model-year 2025.

LWN – 2.8-liter

In 2015 General Motors reintroduced the mid-size Colorado pickup, and with it announced that the 2016 model year would receive a diesel engine option. What followed was a 2.8-liter inline-four-cylinder engine that produced a modest 181 horsepower and 369 lb-ft of torque, while receiving a highway fuel economy rating of up to 31 mpg. While the engine is produced at a GM plant in Thailand, it carries the Duramax name when sold in the U.S. In 2017, the LWN became an option in the Express and Savana 2500 and 3500 series vans, replacing the outgoing 6.6-liter LGH engine.  

LMK – 4.5-liter

Originally slated for the 2010 model year of Sierra and Silverado 1500 pickups, the LMK was to be GM’s first attempt at a modern ½-ton diesel. Unfortunately the great recession and resulting bankruptcy of General Motors shelved the project indefinitely. The LMK was to be a 4.5-liter 72-degree V-8 that produced in the neighborhood of 310 horsepower and better than 500 lb-ft of torque. The engine featured a compacted-graphite iron block and reverse-flow aluminum cylinder heads. One prototype found its way into the public eye in a Chevrolet Suburban test mule shortly before the program was scrapped.

LG4 – 7.8-liter

Little known in the family of Duramax engines is the 7.8-liter, 7800 Series, inline six-cylinder. The hulk of an engine was briefly offered in the Topkick and Kodiak medium-duty trucks from 2003 until GM exited the market in 2009. Built by Isuzu, the LG4 is actually a 6H-series engine. It was offered in configurations that ranged from 200 to 300 horsepower, and 441 to 860 lb-ft of torque.

Cheers to 25 years of the venerable Duramax turbodiesel. That wraps it up for now, but we can’t wait to see what’s next for GM and Duramax.

Now that you’re all fired-up about the Duramax diesel engine, it’s time to shop for your Duramax-powered Chevy Silverado 2500HD and GMC Sierra 2500HD. And as always, contact our knowledgeable sales team for product inquiries and order assistance.