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In 1998, General Motors and Isuzu teamed up to establish engine manufacturer DMAX Ltd to create a brand-new diesel engine that would be the first high-pressure common-rail, direct-injection powerplant to hit the U.S. vehicle market.
2000 – GM debuts the LB7 Duramax diesel engine with 300 hp and 520 lb-ft torque in ’01 ¾- and 1-ton trucks. The 6.6L V-8 turbodiesel engine featured aluminum heads with 32 valves on a cast-iron block, high-pressure, common-rail, direct fuel injection, a fixed-geometry turbo, injectors mounted under the valve covers, and a passive catalytic converter.
2004½ – The LLY Duramax is introduced mid-model year with 310 hp and 605 lb-ft of torque, featuring an improved valve design to make the injectors more accessible for repair. A variable-geometry turbo was added, which used movable vanes in the turbine housing. The vanes dynamically change the volume of air on the exhaust side of the turbo, improving low-end response while retaining a large turbine volume during high engine speeds. Emissions were addressed with the addition of an exhaust gas recirculation system, which routed a portion of the exhaust into a cooler before sending it back through the engine for a secondary burn.
2006 – The coveted LBZ Duramax was introduced for the ’06 model year and featured a number of improvements that enabled the engine to produce up to 360 hp and 650 lb-ft of torque. The LBZ became a quick favorite of tuners, thanks to a stronger block design, larger connecting rods, new piston design, and heads that could handle more pressure. Higher fuel pressure levels, larger fuel rails, six-hole injectors, an improved variable-geometry turbo, and a larger EGR cooler setup were also added. An advanced, 32-bit engine computer helped improve power, efficiency, and emissions. Although the engine was saddled with EGR, the LBZ was the last Duramax offered without a fuel-economy-robbing diesel particulate filter (DPF). This meant the exhaust system could be altered while keeping the truck street-legal. 2006 was also the year GM introduced the six-speed Allison transmission to the Duramax powertrain.
2007 – Along with the new GMT-900 pickup platform for ’08, the LMM Duramax engine was introduced with 365 hp and 660 lb-ft of torque. Along with the large EGR and passive catalytic converter, the LMM was the first Duramax to be fitted with a DPF. The DPF was an active catalytic converter and filter that heralded the new age of active regeneration. This reduced fuel mileage due to the need for extra fuel to be burned when the filter was full of soot. It also dramatically reduced the amount of particulate pollution produced by the engines so they could meet the stringent new emissions standards being introduced by the Federal Government. Despite this fact, engineers figured out a way to be cleaner while making the LMM the most powerful Duramax to date.
2010 to Present – The current version of the Duramax, known as the LML, brings to market a massive 397 hp and 765 lb-ft of torque and meets the most stringent emissions laws to date. Once again, engineers were able to squeeze out another 105 lb-ft of torque while making the engine run dramatically cleaner than the previous generation. This was accomplished with the use of multiple new features, including super-fast-reacting piezo-controlled injectors (which are capable of multiple injections per cycle for optimal combustion), a ninth injector mounted downstream from the turbo to help DPF regeneration, a new EGR system with a cooler bypass, and a new selective catalytic reduction (SCR) system with urea injection. The new engine design also came with a B20 rating, allowing owners to use fuel blends with up to 20 percent biodiesel content without voiding their warranty or risking damage to the engine or fuel system. The LML also added a “smart” exhaust brake built into the turbo, which is activated by the driver using a button on the center console. This exhaust brake has different modes of operation when the truck is in Tow/Haul mode or when the cruise control is activated.
The original Duramax was a vast improvement over GM’s previous indirect-injection diesel, and it beat both Dodge and Ford to the punch when it debuted for the ’01 model year. Two more years would pass before Cummins-equipped trucks were upgraded to common-rail injection, and it was another few months after that before Ford joined the higher-pressure party with its HEUI 6.0L Power Stroke engine. It wasn’t until the ’08 model year that Ford came to market with a true high-pressure common-rail—in the form of the 6.4L Power Stroke.
Until the introduction of the Duramax, GM relied on the all-iron, IDI 6.5L GM V-8, which produced a decent 215 hp and 440 lb-ft of torque in its most powerful configuration. The new, aluminum-headed 6.6L Duramax V-8 hit the market with a very impressive 300 hp and 520 lb-ft of torque in its first configuration, and it has only gotten stronger with age—while still meeting increasingly strict emissions requirements.