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Before we can draw a conclusion on which Duramax engine is the best, it’s necessary to discuss the different engines and the pros and cons of each. Every variant of the Duramax engine has its strong points and at least one weak point. Some engines are more popular than others. For example, the pre-emissions Duramax engines made between 2001 and 2007 are highly sought-after for superior reliability. On the other hand, the more modern engines add more horsepower, torque, and upgrade capability with Duramax performance parts.
The LB7 is the original Duramax engine that arrived in 2001. It’s still highly popular in the used market. Other than LB7 engines sold in California, these engines didn’t include any emission control devices. The lack of these extra emissions parts made the engines highly reliable. Modern Duramax engines often have issues with emissions devices, which don‘t typically last very long. The block of the LB7 is rock-solid and so are most of the internals. The one weak point with the LB7 is cracked or leaky injectors. In most cases, this issue requires injector replacement. The good news is that modern Duramax diesel parts can easily resolve most of the old issues with the LB7. If you’re looking at one now, there’s a good chance that any weak or failing parts have already been replaced.
One of the shortest-lived Duramax engines, the LLY is very similar to the LB7 in structure, parts, and the lack of emissions control. The LLY is capable of getting the largest amount of additional horsepower from tuning only versus any other Duramax engine except the most recent model in the L5P. In terms of weaknesses, the LLY traded the injector issues for overheating issues related to heavy-towing and blown head gaskets. The good news is that head gaskets are easy and cheap to fix compared to bad injectors.
If the LLY’s run was short, the run of the LBZ was even shorter. Still lacking emissions control devices, the LBZ is also one of the most popular Duramax engines. It has the best potential for performance and horsepower additions through various Duramax parts mods and tuning. Built stronger and more durable than previous engines, the LBZ is reliable and powerful. The only weakness is that the pistons are known to crack if you get over 600 horsepower output. However, this isn’t usually an issue for most owners as it takes some $20,000 in mods to get to that level and isn’t necessary for most applications.
Moving into the emissions era of Duramax, the LMM was almost exactly the same as the LBZ, except it featured several new emissions control devices. These devices include a diesel particulate filter (DPF), an oxidation catalyst, and a new EGR. All three of these parts are known to be failure points in this engine. Fuel economy was also lower in this engine as the exhaust treatment uses fuel to work. The good news is that this engine is otherwise the same as the LBZ and features plenty of power and reliability.
The LML Duramax featured a huge leap in performance from the previous engine to put out almost 400 horsepower stock and 765 pound-feet of torque. To accommodate this big power increase, the block, rods, pistons, and main bearing were all strengthened. The high-pressure fuel pump of the previous engine was abandoned for the purpose of helping emissions control in this engine. The smaller pump limits power gains from tuning or bolt-on mods. However, the LML has plenty of power right out of the box, so power-gain mods probably aren’t necessary for most owners. Overall, this engine is great for towing and offers good reliability. The main con is the limited tuning potential.
The L5P is the newest generation of Duramax launched in 2017. It was upgraded from the previous model with 445 horsepower and an incredible 910 pound-feet of torque. The biggest change to the L5P Duramax is the addition of cast-aluminum heads that allow more airflow. A major improvement for the L5P is the addition of a lift pump. This new part relieves stress on the main HPFP, which helps horsepower and fuel system reliability. The L5P is still fairly new, but all signs point to good tuning and modification potential. Overall reliability looks good on paper, but the L5P hasn’t been on the road long enough to rack up big miles and prove its longevity.
It’s hard to rule against the LBZ when it comes to having everything you 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, which is extremely attractive to most diesel enthusiasts. Finally, the LBZ is the last generation of Duramax without emissions control parts, which gives it superior reliability. For those reasons, the LBZ is our choice for the best Duramax engine.
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