When it comes to heavy-duty trucks, two engine names usually dominate the debate: LML and L5P. Built by GM, diesel engines are praised for their power and efficiency. As such, they make heavy-duty trucks perfect for towing and hauling heavy loads regularly.
While these engines are powerhouses, the question is which one reigns supreme? In this post, we look at the performance, reliability, fuel efficiency and durability of the LML and L5P engines to determine which is the winner.
LML VS L5P: Key Differences
Performance
The LML is a 6.6L V8 engine that boasts robust performance. Built by GM, the powerful engine is strong, efficient and powerful. It features a common rail fuel injection and aluminum heads which helped cement Duramax stellar performance.
The turbocharged diesel engine also features a cylinder block and rotating assembly which ensures smoother and quieter engine operation. The strong cast-iron foundation is durable thanks to the induction-hardened cylinder walls.
The L5P is also a 6.6L V8 engine capable of providing 445 horsepower. Thanks to the higher boost pressure from the turbocharger, the L5P produces more power which comes in handy when hauling and trailering.
Besides the 19% in torque, the turbocharged engine is quieter and smoother. In fact, when idle, the noise is reduced to 38%. The powerful engine is capable of running on B20 fuel composed of 80% conventional diesel and 20% biodiesel.
Durable
The LML was first equipped with the Selective Catalyst Reduction, a system that helped to break down harmful nitrogen oxides. Also included was a 9th injector that sprayed fuel directly into the exhaust stream. This helped to clean out the exhaust filter.
The engine was not the only part of the LML designed with durability in mind. GM designed and built every part with durability in mind including the body structure. This ensures that LML vehicles can handle daily wear and tear. Additionally, the durability enables the vehicle to handle rough terrains.
Like the LML, the L5P uses a strengthened cylinder block that includes an induction-hardened cylinder wall. In addition, GM designed a larger diameter crankshaft increasing the bearing surface area.
They also addressed the troublesome CP4 pump by using a brand-new unit designed and built by Denso, a Japanese manufacturer. The new pump, dubbed HP4 produced 20% better flow than the outgoing unit.
Thanks to all these upgrades and more, the L5P is durable and reliable. Whether you’re hauling or trailering, the heavy-duty truck will provide exceptional performance.
Fuel Efficiency
When it comes to fuel efficiency, the 6.6L V8 engine equipped in the LML is fuel-friendly. When unloaded, the fuel economy was 24 mpg at a speed of 55 MPH on the highway. When city driving, the fuel economy was 15 mpg.
The L5P has an average mileage of 24 mpg on highways and 18 mpg in cities. There are changes drivers can make to their diesel engines to achieve extra mpg. For starters, one can tune the engine for extra mpg.
As you already know, diesel engines produce high low-end torque, and manufacturers want to reduce emissions. Due to this conflict, increase rpm and trade it for torque. If you can tune your truck and shift torque back to the low end, you’ll get more power with less energy. This will also improve gas mileage.
Making upgrades to the air intake system is another way to get extra mpg. When you replace the air filter and make modifications to the airbox, you let more air into the combustion chamber. The more clean air flows into the combustion chamber, the more efficient the combustion process.
Another modification you can make is getting a new fuel filter. A clean fuel filter will give you the best mileage and performance.
Towing Capacity and MPH
The LML has a towing capacity of 14,500 pounds, while the L5P has a towing capacity of 20,000 pounds. The reason why the L5P towing capacity is higher than that of an LML is that the L5P engine is designed and built with heavy hauling in mind. As such, the L5P is ideal for towing large trailers or for hauling heavy loads.
The LML can accelerate from 0 to 60 MPH in approximately 5.6 seconds, while the L5P takes 7.1 seconds to reach a similar speed. While the LML and L5P have similar turbocharged V8 engines, the LML engine is faster by 1.5 seconds than the L5P engine.
What you need to know is that you can mod the LML engine to generate more power and speed. The stock turbo of the LML engine is one of the worst because it’s good for 525whp before you need to upgrade it.
To generate more power and speed, you can upgrade the stock turbo with an aftermarket option capable of generating 650whp. If you want to push past 700whp, you can get a fixed geometry turbo.
Besides the turbo, you can make upgrades to the air intake system. Adding the air intake system will amplify the power gains for the turbo and intake. In addition, it will reduce stress on the engine by allowing it to breathe more easily.
We recommend going for open intake systems as they provide more airflow to the combustion chamber over closed box systems. This is true if you’re shooting for 600+ whp Besides the intake system and turbo, you can also upgrade the tuner.
Upgrading the tuner alone will add over 100whp and more than 200wtq. Together with the intake, you help the turbo and engine breathe better. This allows your engine to generate more power and speed.
Final Thoughts
The decision between the LML vs L5P engine is a personal preference. However, from our research, the L5P boasts of superior performance and power. As such, it’s best for towing heavy loads or trailering.
When it comes to the LML engine, it’s durable and reliable thanks to the many upgrades that GM made to the engine. However, when it comes to power in comparison to the L5P, it lags behind.
The good news is there are aftermarket options that you can use to mod your LML engine. From the air intake system to the fuel filter and turbo, all these options can help boost the performance of your LML engine.