History of the Duramax Engine

The Birth of DMAX

General Motors had fallen behind in the market in the late 1990's in regards to their Diesel Engine offerings, with the Detroit Diesel outputting abysmal power and torque numbers it was time for something new. With 3% of the market share, they knew they had to change the direction of this segment quickly.  In comes the partnership with the leader in diesel engine technology, Isuzu. This was the beginning of one of the best partnerships in the industry. In 1998 GM and Isuzu established a new engine manufacturer, DMAX Ltd. they invested in a 650,000 square foot facility located in Moraine, Ohio and was split 60% owned by GM and 40% owned by Isuzu. Isuzu had originally planned to release this new engine around 2003 but GM put it on the fast-track to be sure it could be available for production in 2001. The design was also split up between the two corporations with Isuzu in charge of the main engine design, while GM was put in charge of the common rail fuel system that allowed for the engine to be much more efficient than other fuel systems found in the competition's vehicles. The engine is a 90-degree V8 layout, featuring an overhead valve design with 4 valves per cylinder, the engine also utilized direct injection and was turbocharged to produce the power required to beat the competition. 


The LB7 Duramax was introduced in 2001 and was an immediate success, earning best in class in multiple categories and even out performing the comparable gasoline power plants. It was initially rated at 235 horsepower and 500 lb.-ft. of torque which was right in line with the competition, same power and torque as the intercooled 7.3L Power Stroke Diesel and the 5.9L 24 valve Cummins. The common rail injection is what really set this engine apart from the rest, aside from being smoother and quieter than the competition it was easy to add power! GM kept the power output the same for the first 2 years of production before they saw the need to stay ahead of the competition. In 2003 the LB7 received a major update in power, going up to 300 horsepower and 520 lb.-ft. There were minimal changes for the 2001-2004 Duramax other than the power output, although there were 2 different configurations available. Due to California’s strict emissions regulations, there was a California emissions truck and Federal emissions truck, the CA trucks had an Exhaust Gas Recirculation (EGR) system and a Catalytic converter. This later became standard on all engines moving forward.


With Ford releasing their 6.0L Power Stroke engine it was evident that an update was needed for the Duramax. In comes the LLY, after seeing some injector issues with the LB7, the injectors and valve covers were redesigned for improved reliability and allowed for easier replacement. The LB7 featured injectors under the valve covers and was quite the job to replace them and it was often recommended to replace all 8 injectors at a time. The LLY injector featured a completely new design and proved to be much more reliable than the original. The turbocharger was also a welcome upgrade, the LB7 featured a fixed vane IHI turbo that was reliable but was not as efficient as the new variable vane technology that was now available from Garrett Turbochargers. The size and design of the turbo was all new and now had variable vanes to improve drivability and performance as this is the largest turbocharger, 62mm, ever fitted to a factory Duramax. This resulted in an increased power output of 310 horsepower and 520 lb.-ft. Unfortunately this did not come without its own share of issues with overheating causing head gasket issues early on as the radiator and intercooler remained unchanged from the original LB7 Duramax and were undersized.


In 2006 the holy grail of Duramax engines was introduced, the LBZ. Not only did this rendition solve many of the overheating problems, the power output was upped to a staggering 360 horsepower and 650 lb.-ft. of torque blowing past the competition! The LBZ utilized a 1mm smaller turbocharger but maintained the variable vane technology as it soon became a standard in the industry. The power increase was thanks to the improved block design, stronger connecting rods, new piston design, slightly revised fuel system and a whole new computer system. The LBZ engine block has additional reinforcement in the casting creating a more rigid design than the previous iterations. The new fuel system used a new injector nozzle and improved fuel rails that allowed for higher pressure and better efficiency. Using a 32-bit CAN Bus type computer system made this a favorite for tuners as it is more reliable than the previous computer system on the LLY and LB7 Duramax’s. This did not last long unfortunately as it was only available for 2006 and early 2007 GM light duty trucks. Emissions regulations were getting more and more stringent and it called for a massive overhaul of the exhaust and emissions systems.


In 2007.5 the next generation of Duramax, LMM, carried over many of the parts from the short block of the LBZ. It also increased the power output slightly with a bump to 365 hp and 660 lb.-ft. of torque. The major difference came in the form of a Diesel Particulate Filter (DPF) the addition of this robbed fuel economy as it used fuel to burn off the diesel particulate that was being captured by the DPF by performing an active regeneration. A larger and more efficient EGR cooler was fitted to this engine to reduce cylinder temperatures and reduce emissions. This stayed for a while until it was replaced by the next generation of emissions.


In 2011 the LML Duramax was introduced, it had a host of new upgrades, there were very few parts that were carried over from the previous generation trucks. The injection system was overhauled again with a massive change to piezo electric injectors, this utilizes a stack of Piezo crystals that would expand and contract with electrical current, this happened much faster than the previous solenoid injectors would allow for, this meant you could perform multiple injections per combustion cycle for optimized combustion. In addition to this the LML received a whole new injection pump, CP4, that was able to hold a higher pressure for longer durations than the previous injection pumps. It was not immediately recognized that the CP4 had a design flaw that could lead to a catastrophic failure and require a complete fuel system replacement. The emissions system was completely new as well with the introduction of Diesel Exhaust Fluid (DEF) that was injected into the exhaust stream and when combined with heat and the materials from the Selective Catalyst Reduction (SCR) caused a chemical reaction to decrease the amount of harmful NOx emitted from the exhaust system. There was still a DPF on the exhaust as well, this was mainly to reduce the amount of soot that was pushed out of the tailpipe to meet the stringent requirements set by the Environmental Protection Agency (EPA). While all of the emissions systems implemented may seem like the power would be reduced as well, the LML actually produced a tremendous 397 horsepower and 765 lb.-ft. of torque becoming a class leader, until the 6.7L Power Stroke edged it out in late 2011. Additional cooling upgrades were made as the towing capacity increased substantially. It was in 2012 when DMAX Ltd. hit a major milestone, producing 1,500,000 Duramax engines, the joint venture with GM and Isuzu proved to be a massive success and GM has received many awards based on this product. 


In 2017 there was an entirely new engine with no shared components from any of the previous models, new suppliers, and major design changes were made. The L5P Duramax was introduced and took the market by storm with its healthy 445 horsepower and 910 lb.-ft. of torque. The air flow was one of the major improvements as there is an entirely new head design and intake runners that allowed for much better flow to the cylinders and improved efficiency.  The entire bottom end was also redesigned with stronger rods, pistons, block and crankshaft. This was the largest change that had been done to the Duramax engine since its inception. The fuel system was changed from Bosch to Denso, and went back to a solenoid style injector instead of the Piezo electric injectors that were fitted on the LML, along with this came the welcome upgrade to the finicky Bosch CP4 injection pump, the Denso HP4 this eliminated the dreaded catastrophic failure that can occur causing the entire fuel system to be replaced. Along with a new supplier for the fuel system, the turbocharger was also a massive change, switching to a Borg Warner turbocharger that maintained the use of the variable vane technology but utilized an externally actuator versus the olderstyle Garrett turbochargers that housed the actuator within the body of the turbocharger. The emissions system was completely overhauled as well with a SCR located directly off the back of the turbocharger to quickly heat up the SCR to operating temperature so it can operate efficiently. This engine continued the use of a DPF, EGR and DEF system to maintain compliance with the EPA. In 2017 DMAX Ltd. produced their 2,000,000th engine, this is a massive milestone and shows the success that the American plant has had with the Duramax Engine program. 


Power output stayed the same until the 2024 model year when it increased to an incredible 470 horsepower and 975 lb.-ft. of torque. There have been many slight revisions to the L5P to achieve this output but at this point has not been publicly released as to what exactly those revisions entail.