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Top Mods For The Duramax L5P Engine

The Gen 1 L5P Duramax engine was first released in 2017 and became one of the most wanted GM Diesel engines.

"The 6.6l V8-turbodiesel engine comes from the factory with whooping 445 HP @ 2,800 RPM and 910 lb-ft (1,234 Nm) of torque at 1,600 RPM."

However, this beast has a lot of room for improvement as it’s equipped with very restrictive -and problematic- anti-pollution systems and noise reduction elements.

In addition, the original tuning is quite conservative, programmed for the average user, but far from the engine’s full potential. If you are one of those seeking to squeeze the engine up to its very last HP, then stay tuned, as we have created this guide just for you.

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Image Source: enginebuildermag

High-Flow Air Filter / Cold Air Intake

The L5P's stock air intake is better than you would expect; it provides the engine with enough airflow for stock and mildly tuned ECU software. However, it’s one of the easiest and most accessible parts to replace. A filter upgrade increases the engine power and makes it sound amazing.

You can choose between two options: 

  • Drop-in High-Flow Air Filter:These products replace the highly restrictive stock air filters, providing increased airflow and excellent filtration power. Most models are washable and reusable. This is a cool and affordable upgrade if you won’t settle with your truck’s stock power but don’t want to do significant modifications. Brands like K&N offer excellent high-performance drop-in filters for the L5P Duramax.

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Image Source:hpsperformanceproducts

  • Cold Air Intake (CAI): By installing a cold air intake, you will get rid of the stock intake piping, including the muffler, which effectively removes most of the engine's amazing sound. A proper CAI allows the engine to breathe better, reducing the turbo lag and making the combustion more efficient, achieving a power gain of more than 10%. Besides, cold air intakes enhance the looks of your engine, providing a clean and sporty look. SB Filters, for example, makes an outstanding kit for the Duramax, but there are plenty of choices in the market. You can find more info about CAIs in this blog post.

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Engine tuning software

Reprogramming the engine’s computer is an effective way to get the most out of a modern engine. You can choose a custom dyno tune, which involves taking the truck to a tuning shop where a professional tuner will reprogram the engine according to your engine mods and power and torque goals. Even though this method is personalized and tailor-made for each truck, it’s expensive, and you often get only one tune.

On the other hand, you can choose to buy a tuning box or calibrator, which has become a very popular mod among truck owners. These devices allow users to load different presets to the engine. Tuning boxes can have different programs that you can toggle depending on your driving needs and occasion, for example:

  • A Towing or High-Torque Program.
  • A High HP program oriented on high HP, increased throttle response and acceleration.
  • A Fuel Economy program to save fuel during long trips or urban driving.

These tunes are not as perfect as custom ones, but they allow the ECU to adjust its parameters to take the most out of your engine mods, if any. Also, most models allow users to log some engine parameters, which you can save and send to a tuner to get a tailor-made program. These programs are not as effective as the ones created using a dyno, but they work great and are far less expensive than a customized dyno tune.

Lastly, programming the engine’s computer is essential to avoid triggering warnings and preventing it from entering into “emergency mode” when installing an L5P Delete Kit (we will come to that in a bit). These kits allow the removal of some or all emission systems, which has many advantages. At Spelab, you will find an excellent programmer for the 2017-2023 Duramax, the OBDii Flash Delete Tuning Interface, which allows you to adjust some engine parameters by yourself, eliminate triggers caused by installing an L5P Delete Kit, and upload 3rd party performance software to the truck, among other great features.

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Image Source: maxxecu

Turbo Up Pipes Upgrade

Another great way to get more horsepower from the L5P engine is upgrading the turbo up pipes for high-flow up pipes.

The turbo up pipes are connected to the engine’s exhaust manifolds and feed the turbocharger with the exhaust gases that make it work.

The factory turbo up pipes serve their purpose well in a stock engine, but like most OEM parts, they are heavy, restrict the airflow, and are muffled. Upgrading them is a relatively inexpensive mod that optimizes the turbo airflow and reduces the turbo lag, enhancing its efficiency. This translates to increased boost, HP, Torque, and enhanced engine performance.

Turbo Downpipe

A downpipe upgrade is also an effective mod on all turbo vehicles, and the L5P engine is no exception. The Duramax stock downpipe is very restrictive because of its small diameter and shape (it seems it has been smashed with a sledgehammer). 

High-flow downpipes allow the turbo to evacuate gases faster, which results in reduced lag, an increased boost, and more HP for your engine. A high-flow downpipe reduces the turbo lag and naturally increases the boost, unleashing the turbo’s full potential. A larger downpipe increases the stock engine, and when combined with other upgrades like a Cold Air intake and a nice engine recalibration, you can expect serious power gains of more than 50HP in an engine like the 6.6 Duramax. Besides the power gains, high-performance downpipes give the engine an aggressive sound that helps create that adrenaline rush you feel when you hit the gas and unleash more than 450HP.

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L5P Delete Kit

As we mentioned earlier, the Duramax V8 turbodiesel engine comes with a series of emission control features that affect the engine’s peak performance and fuel economy and are one of the primary causes of breakdowns in the long run.

Eliminating the emission systems is an excellent way to reduce the odds of future costly replacements. It’s also the only way to install a full high-performance exhaust system, which is an essential part of the most extreme tunings, and it’s also the only way to get rid of the troublesome and HP-killing DPF.

Another problematic component is the EGR (exhaust gas recirculation) valve. All diesel owners know the troubles related to these valves and how they clog up and render the engine less and less efficient as it accumulates more miles.

The DPF, EGR, DEF, and CCV systems are designed so that in case of malfunction (or removal; the engine identifies a removal like an error), the engine computer is designed to trigger all the alarms and set the engine in emergency mode, rendering almost undrivable.

That’s why you should reprogram the engine computer before removing any of these systems and install a series of electronic devices that ‘fool’ the computer so it doesn’t notice the missing emissions components.

Removing these items can be illegal in your state; that’s why we advise you to check your location’s local regulations before removing any of these components. However, it’s essential that our company and all high-performance parts manufacturers only recommend making these mods for off-road use only. You can find more information about this in the following article.


Below, you will find some of the best L5P delete parts and the full L5P delete kit, which includes all you need to remove all the unnecessary, restrictive, and potentially problematic emission controls from your truck:


  • L5P EGR Delete kit:This kit includes everything you need to remove the problematic EGR valve. Besides, removing this valve improves the exhaust flow and reduces the turbo lag, resulting in a faster throttle response.
  • L5P DPF Delete Kit / Downpipe Back Exhaust System:High-flow exhaust systems help enhance the engine sound, squeeze some HP on mildly modified engines, and are extremely necessary for extreme, high-output tunes. The larger and enhanced piping and the elimination of the DPF filter reduce the engine’s backpressure, allowing it to evacuate exhaust gases faster. As the exhaust gases are eliminated faster, the engine can grasp cold, fresh air sooner, resulting in more HP. The diameter of the exhaust is a matter of preference, but it’s also related to the turbo's size and the engine’s power. When installing a DPF delete kit, you will need a set of emulators to trick the engine ECU and remove all ‘open circuit’ signals that cause the removal of the DPF and NOX modules.
  • L5P Delete Kit:This kit brings all the necessary to make a complete emissions delete on your truck. It includes all the delete kits you can imagine and a programmer that removes the error codes and works as a scan tool, among other amazing functions.

L5P Delete Kit

Other Mods Worth Consider

The list of upgrades available for the L5P engine is endless. Below, you will find some honorable mentions in our top mods list.

Big Turbo

The stock turbo is another significant limitation regarding how much HP you can get from the engine. With proper tuning software and hardware, a big turbo will allow you to break the 600HP barrier and get in the 700+ horsepower range.

Transmission Upgrades

Auto transmissions are commanded by a computer called a TCM (Transmission Control Module). The modern L5P TCM allows you to adjust parameters like the torque converter’s parameters, shifting points, and other values that will help you make the most of your tuning. Some programs can also modify the clutch force to increase its clamping force, reduce friction, and extend your transmission’s lifespan.

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Image Source: dieselarmy

Water Methanol Injection

Another significant yet affordable upgrade is installing a water-methanol injection kit. These kits consist of a bomb and one or several nozzles (depending on the intended power gain) that spray a mist of water and methanol into the engine, reducing the combustion chamber’s temperatures and the risk of piston knocking. In an engine like the L5P, you can gain about 60 HP just from the benefits of the cool mixture fed into the engine. Besides, the reduced temperatures allow more aggressive tunes, which can lead to gains beyond 80+ horsepower. Snow Performance, for example, is one of the most recognized and popular water-methanol injection kit manufacturers, and it offers a special kit for the 6.6 Duramax.

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Image Source: ebay

Wheel Spacers

This mod is not for the engine but is an excellent complement to the modifications mentioned before. A set of wheel spacers not only the vehicle’s track, providing more stability but also gives it that bad look that matches what’s inside the hood.

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Final Words

We made this list to inspire you and give you an insight into the best mods you can do to upgrade a L5P Duramax. We hope you have enjoyed it as much as we enjoyed sharing it with you. If you would like us to expand on some of these tunes, or you would like to share some pictures of your builds, please leave a message in the comment section below. We are always happy to help and see what you guys are up to!

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