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Which Duramax engine is the best? Reaching that conclusion takes a lot of work: you have to weigh the pros and cons of each engine model. Each Duramax engine has its strong points, plus a drawback or two.
Some truck owners seek out the pre-emissions Duramax engines made between 2001 and 2007 for their superior reliability. Other truck owners prefer the modern engines for their extra horsepower and torque –plus the ability to upgrade their capabilities with Duramax performance parts.
The original Duramax engine is the LB7, which has been highly sought after since its introduction in 2001. Unlike LB7 engines sold in California, this engine model didn’t include emission control devices, which contributed to its reliability. In comparison, modern Duramax engines have emission device issues that tamper with their longevity.
The LB7 block and its internals are mostly rock-solid; this engine’s only weak point is cracked or leaky injectors, which usually require an injector replacement. You can resolve most of the old issues with the LB7 by installing modern Duramax diesel parts.
If you’re trying to buy an LB7 now, its weak or failing parts have likely been replaced by now.
The LLY, one of the most short-lived Duramax engines, is very similar to the LB7 in structure, parts, and lack of an emissions control system. However, the LLY gains large amounts of additional horsepower through tuning only—more than any other Duramax other than the L5P.
The LLY does have some pronounced weaknesses: it experiences overheating issues caused by heavy towing and blown head gaskets. Fortunately, head gaskets are easier and cheaper to fix than bad injectors.
While the LLY’s run was short, the LBZ’s was even shorter. Despite being short-lived, the LBZ remains one of the most popular Duramax engines. Although it lacks emissions control, ito has the best potential for mods and tuning, which can improve its performance and horsepower.
The LBZ is also incredibly reliable; it’s built stronger and more durable than previous Duramax engines. Their only weakness is that their pistons are known to crack if you surpass 600 horsepower output.
Since it can take roughly $20,000 worth of mods to reach that level of performance, it won’t be an issue for most owners.
The LMM marked the emissions era of Duramax engines. This engine is almost identical to the LBZ but includes several new emissions control devices, including a diesel particulate filter (DPF), an oxidation catalyst, and a new EGR. All three of these emissions systems are well-known failure points in this engine.
Since the engine’s exhaust treatment uses fuel to work, this engine also had a lower fuel economy. Despite these drawbacks, the LMM is almost identical to the LBZ, so it’s incredibly powerful and reliable.
The performance of the LML Duramax is leaps and bounds ahead of its predecessor. It’s capable of nearly 400 horsepower stock and 765 pound-feet of torque. To help accommodate this significant power increase the lock, rods, pistons, and main bearing were all strengthened.
The LML also abandoned the previous generation’s high-pressure fuel pump to support its emissions control. While its smaller pump limits the amount of power it can attain from tuning or bolt-on mods, the LML has plenty of power right out of the box.
Most owners won’t need power mods. Its greatest drawback is its limited tuning potential, but overall, this engine is great for towing and incredibly reliable.
Launched in 2017, the L5P received several performance upgrades from the previous model, including 445 horsepower and a whopping 910 pound-feet of torque. However, the biggest change in the L5P Duramax engine is the addition of cast-aluminum heads for greater airflow. Another major improvement is the addition of a lift pump, which relieves stress on the main HPFP.
This improves the engine’s horsepower and fuel system reliability. It also has the potential for tuning and modification. The L5P sounded like a reliable engine on paper and has since proven its rock-solid durability. In the 2024 model year, the L5P Gen2 further increased its horsepower and torque.
The L5D Duramax diesel engine is a 6.6-liter V8 designed for medium-duty applications, such as GM’s Chevrolet Silverado 4500HD, 5500HD, and 6500HD trucks. It offers a balance of performance and efficiency, producing approximately 350 horsepower and 700 lb-ft of torque, though these figures may vary slightly depending on the specific vehicle configuration.
The engine features a variable-geometry turbocharger, which enhances performance and responsiveness across a broad range of operating conditions. It also utilizes a high-pressure common rail direct injection fuel system to ensure precise fuel delivery, maximizing power and fuel efficiency.
Additionally, the L5D includes advanced emissions after-treatment systems, enabling it to meet stringent EPA and CARB emissions standards. Tailored for durability and reliability, the L5D is well-suited to demanding commercial and fleet operations.
It’s hard to rule against the LBZ; it has everything you could want in a Duramax diesel. The LBZ improved upon the previous two engines, which had significant weaknesses in the injectors and head gaskets.
The LBZ also offers excellent tuning and modification potential, making it extremely attractive to most diesel enthusiasts.
The LBZ is also the last generation of Duramax without emissions control parts, making it more reliable than any subsequent engine. For those reasons, it is our choice for the best Duramax engine.
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