6.6L L5P Duramax Specs, Tow Ratings, And Model Year Changes

2017+ Chevy HD and GMC Diesel Trucks

The GM 6.6L L5P Duramax joined the party with the Chevrolet Silverado HD and the GMC Sierra HD trucks back in 2017. While the exterior of this truck looked very similar to the LML Duramax, except the new hood-scoop, this L5P engine barely resembles the LML at all.

The displacement is practically all it shares in similarities with the LML. The 6.6L L5P Duramax engine provides significantly superior performance specifications, towing ratings, and durable reliability than the LML. 

6.6L L5P Duramax Specs, Tow Ratings, And Model Year Changes

Today, we are going to look over the changes that took place to ensure that the L5P Duramax engine is evermore powerful, capable, and reliable than the previous generations of Duramax. 

ATVA Online has you covered with our comprehensive guide to all things relative to the 6.6L L5P Duramax Diesel. 

The Engine 

Much like the engine designs of the past, the L5P Duramax engine has a 90-Degree V-8 configuration. The block is a cast-iron for superior strength, included with induction-hardened cylinder walls and five modular main bearings for even stronger durability.

The engine block of the L5P includes a deep-skirt design, it has four-bolt, cross-belted main caps. This feature helps to bolster the engine block and enables much more accurate locating of the rotating assembly. 

Then, there is the die-cast aluminum lower crankcase, which adds extra strength to the engine block, while this also simultaneously acts as the lower engine cover.

This helps the GM achieve some extra weight savings also. It also has significantly larger crankshaft rod journals when compared to the LML, this allows the use of a stronger crankshaft, as well as more bearing area, to be able to sustain higher cylinder loads.

These rod journals are also cut-then-rolled, this helps to strengthen the journal-web connection. The crankshaft itself is also made of forged-micro-alloy steel. 

The connecting rods are also forged with a powdered steel alloy, along with a fractured cap design, this is used with a 45-degree split-angle design too. This type of design allows for a larger diameter of rod bearings to pass through the cylinder bores during the assembly progress. 

The Cylinders 

Now, taking a look at the cylinder head design. The cylinder heads you may recall from previous Duramax generations are still aluminum in the L5P.

They have four valves per cylinder, and the casting of the aluminum head uses new, double-layer water core designs.

This simply means that the design arranges the water cores in layers, which results in a much stronger head structure in the cylinder head, with superior coolant flow properties. 

There were other revisions added as well, such as airflow passages which help improve the airflow and increase performance.

Durable Pistons

One area where the L5P has advanced over the LML is in its revised piston design which results in much more advanced and amazing durability.

These are new cast-aluminum pistons, which have a taller crown area, and a remelted combustion bowl rim. This process of remelted extends the life of this rim and extends the durability.

Once these pistons are cast the bowl area is also reheated, this then creates a finer metal grain structure that is attributed to a longer life. These pistons also don’t use pun busing, reducing weight and improving performance. 

Extra Engine Info 

The GM engineers added a better lubrication system and oiling circuit to the L5P Duramax engine, they did this to ensure that the engine can hold up its high-performance numbers.

The enhanced oiling circuit offers a higher flow, as well as a dedicated turbocharger feed.

Having this in place provides a fast oil delivery and an increased pressure at the turbocharger.

The piston-cooling jets at the bottom of the cylinder bores were also sized up so that they can provide twice the amount of engine oil to the piston crowns. This feature allows to further lower engine temperatures and increase reliability.

An integrated oil cooler is also one of the features of the L5P that offers an astounding 50% more capacity than the LML’s engine does. 

The L5P also has a new two-piece pan for greater NVH reduction and durability, the bottom piece is made of laminated steel which helps to reduce vibration, whereas the top piece offers a more rigid surface. 

Performance of the L5P Duramax 

This newest Duramax, the L5P is the absolute King of capability yet. It produces a jaw-dropping 445 horsepower and has 910 lb-ft of torque in stock form.

In many ways, it is still similar to the LML, as it uses the same 6.6L displacement still. Despite its similarities, the engine itself is very dissimilar.

There have been numerous big changes that resulted in a 48 horsepower increase and 145lb/ft of torque in comparison to its predecessor- the LML.

There have also been changes in the Borgwerner Variable Geometry Turbocharger, as well as a fuel system overhaul, and a fully-functional hood scoop intake system as well!  

Though these are not the only things that make the L5P amazing, there are plenty of other features that give it, its glitz and glam that it fully deserves. Let’s have a further look at these further qualities that give the L5P its kick. 

Borqwerner Variable Geometry Turbocharger 

The L5P Duramax has a fantastic variable geometry turbocharger, gifted by Borgwener which is electrically actuated and electronically controlled too.

While Duramax has usually be equipped with Garrett units, this time they have gone with Borgwerner and so this is actually a big shift for them.

This Borgwener variable vane turbocharger has a billet compressor wheel that supports 11 blades and has an inducer that is slightly bigger than ones found in previous Duramax generations. 

The maximum boost pressure is superior to the LML and is 28 psi, this ensures better performance. 

The turbocharger here also acts much like an exhaust brake, which can be also found in the LML but this one is simply far superior. This turbocharger was revised so that it can provide you with greater exhausted braking abilities. It was given a reduction in internal leakage which was able to allow for more exhaust energy to be captured during the exhaust braking. 

This system is fantastic because the factory exhaust brake system gives you peace of mind and comfort when you are towing, as it adds back pressure into the exhaust system, which slows the vehicle down during deceleration or downhill driving- which is definitely something that you want on your side in that scenario. 

If you expect to be towing or to be the first person that people call when they need a tow, then this is a must-use feature that the L5P provides. Simply because it will significantly extend the life of the brake pad, and it will make big trailers or heavy loads much easier to manage, especially if you can see yourself driving in mountains or other unking terrains.n

Fuel System Overhaul 

The L5P Duramax also has a common rail direct-inject fuel system. Which is not supplied by Bosch, unlike many fuel systems you may be familiar with, such as models as recent as the LML.

The entire L5P system is made by Denso, it operates at 29,000 psi, or 2,000 bar, however, you rather view it. This helps to provide cleaner fuel to burn, reducing harmful emissions (fantastic for the more eco-friendly truck enthusiast), and also provides a  much smoother better performance. 

Denso HP4 Injection Pump 

As we have already mentioned Denso, let’s have a little further look into what the Denso Injection pump does for the L5P.

This injection pump is a star, and it is much more different than the Bosch units you may be used to in older trucks.

For a start, it has three high-pressure cylinders, a filter screen that catches debris and particles from the inlet of the pump, and it is supplied a steady stream of fuel from the first in-tank lift pump which is found on a factory Duramax. 

Wondering if you heard us right? We certainly were. But, yes! The L5P Duramax actually comes from the factory with a built-in lift pump! What does this do? Well, it improves the longevity of the injection pump because it takes a heavy workload off of it.

In previous engines you would notice that the injection pump would have to multitask, having to both pressurize the fuel for the injectors, which also siphoning fuel from the tank.

This was inefficient and did cause a stream of issues on trucks with any performance modifications. So, we think that this was a great idea. 

Denso G4S Gen 3 Injectors 

So along with the injection pump by Denso, there is also the Denso G4S Gen 3 Injectors.

The L5P Duramax’s injectors are solenoid injectors, instead of the piezoelectric ones you might find on models such as the LML Duramax.

These types of injectors are much less complex but due to their advanced technology they offer a performance that is similar to the piezo-style units.

These Gen three, G4S injectors can support up to seven fuel delivery events per any combustion cycle.

This, therefore, gives the L5P lower NVH whilst simultaneously providing greater efficiency and cleaner emissions (again one for the eco-friendly truck enthusiast) 

The New Intake System. 

So, we have already looked at some of the most critical and most fantastic upgrades that come with this L5P system. However, we still have many to go. One of these critical elements is the L5P Duramax’s impressive, brand new intake system that helps to give it its impressive specs. 

GM added in a hood scoop, as you can tell when you look at the model. This provides more cool and dense air to the engine.

Cooler air will have a greater density which will result in a much better combustion. Having this will improve the power, reliability, fuel economy, and it will again, help reduce emissions. You will be able to feel this fantastic system as you drive along. 

This system will help to keep the engine cool. Especially if you are driving along with a heavy-load or in difficult conditions, which trucks tend to be made for, this one is clearly made to be even more made for this.

Additionally, its addition of a fully functional hood-scoop providing constant cooler air is a fantastic design because it provides air derived away from the engine. Also, provide dramatically more air than you may be used to in your normal intake system. 

You may be surprised to learn that this hood scoop actually provides up to 60% of the air to the Duramax engines. The air filter housing then draws the remaining 40% air from a dry location in the front fenders.

Best the air from the air filter housing enters the combustion chamber, it will mix with the cooler air that is sourced from the hood inlet.

This means that drawing air from different locations guarantees that even if the bone was to become blocked then the other can still adequately supply cool air to support the engine. Whatever happens, your engine gets the air it needs. You are always prepared. 


When looking at the air cooling system, GM took special precautions to make sure that the air received by the new intake system stays clean and dry as well. Therefore an air/water separator mechanism exists within the system.

It works well and effectively by doing the following; air will enter an expansion chamber that contains a very sharp, 180-degree turn when on its way to the air filter housing.

As it makes this sharp turn velocity changes where any moisture or humidity forms larger droplets that are flung against the outside housing wall. Here it will drain through a valve. 

Allison Transmission

We still haven’t looked at one of the most important features of the infamous Duramax trucks- the Allison Transmission. It is considered that this transmission is one of the most durable of any and any duty trucks.

The L5P Duramax uses a 6-speed Allison Transmission in their models from 2017-2019. Then in 2020, they switched it up and used a 10-speed automatic Allison transmission instead of the previous 6-speed. 

This 10-speed Allison Transmission puts out crazy power to the ground and does so better than the now overshadowed 6-speed.

It lays down much more torque in low gears, which ends up giving the result of a smoother and shorter shift as you drive. It also gives a fantastic performance, as it can put all 910 lb-ft of torque to the ground in first gear! 

The transmission can also enable smart engine braking, which will in turn extend the life of your brake pad, and we all want that! It also has another useful feature.

This Allison transmission eliminates the need for an aftermarket PTO (Power Take Off Unit). The 0-speed Allison transmission features an integrated, chain-driven PTO system that is fully able to power equipment at job sites too, just with a click of a button in the cab! 

The Engine Specs 

Manufactured Years:


Engine Design:

90-Degree V8 Turbocharged Diesel


2017-2019: Allison 1000 6-Speed Automatic

2020+: Allison 10L1000 10-Speed Automatic


6.6 Liters or 403 Cubic Inches


4.055″ or 103 mm


3.897″ or 99 mm

Block Material:

Cast Iron

Cylinder Head


Cast Aluminum

Intake Manifold Material:

Cast Nodular Iron


Forged Steel

Camshaft Material:


Connecting Rods Material:


Compression Ratio:


Firing Order:



BorgWarner Variable Geometry Turbocharger


Fuel Injection:

Direct Injection, Denso High Pressure

Common Rail with 29,000 Max PSI

Injectors: New Denso G4S Gen III Solenoid Style

capable of 7 injections per combustion sequence


32 Valve (4 Valves per cylinder) OHV or Overhead


Engine Oil Capacity:

10 quarts or 9.5 Liters

DEF Fluid Capacity:

7 Gallons

Cooling System


31.4 Quarts or 29.72 Liters


B20 Biodiesel Blend or Ultra Low Sulfur Diesel

Fuel Tank Size:

36 Gallons Standard

Max Engine Speed:

3,450 RPM (Revs per minutes)

Max Braking Speed:

4800 RPM (Revs per minutes)


445 Horsepower At 2800 RPM (Revs per minutes)


910 lb/ft at 1600 RPM (Revs per minutes)

History and Year Changes of the L5P Duramax. 

Let’s have a look at the changes and ways that the L5P Duramax has changed over the years and how it has grown.

What are the major stark differences between the 2017 model and the newest 2021 model? Is it improving or are there certain things to look out for in certain year models? Let’s have a look...


In 2017 we first saw the 6.6L V-8 L5P Duramax Diesel engine, introduced on the Chevy HD and GMC HD trucks.

The newest L5P is the most capable Duramax so far and it offers 445 horsepower at 2,800 revolutions per minute, as well as 910 lb-ft of torque at 1,600 revolutions per minute. 


In 2018 a few improvements were made, these improvements were primarily in the style and the tech. New colors were added as well as a 7” display standard on the base models.

The GMC also got a new Denali grille design, while the Chevy got a New High Country and Z71 grille design. There was also a tire pressure alert added on the TPMS system, and there was a new year-view camera standard on all models with a cargo box. 


2019 saw no significant changes, this may simply have been because they were biding their time to completely blow us all away in 2020. 

2020- REFORM! 

When 2020 arrived we were all shocked, as the Chevy HD and the GMC HD trucks were overhauled. A new-body style was added in, new towing technology became available. 

The L5P Duramax is also updated to help support a new maximum towing capacity of 35,500 lbs. Which is effectively a 50% increase from the 2019 models.

It also sports a 10-speed automatic Allison transmission, which replaces the 6-speed unit that is found on the older L5P variants. It also has a 6.6L gas engine in this model as well. 


The 2021 version included a tech and trim refinement. It included a Carhartt special edition added in the Chevy. There is also a wireless Apple CarPlay and Android Auto added into this edition, so the tech savvy who like to have their Apple devices easily linked up to their truck. 

There is also a Bed view camera available on WT, custom, and LT models as well. There is an EZ lift tailgate that is available for LT models. And a safety confidence package that is available on WT and custom models as well. 

The Gm heavy duty trucks equipped with the L5P Duramax engine look almost identical to the LML Duramax from 2017 until 2019.

The differing factors are by looking at their exterior hood scoop. In 2020 Chevrolet and GMC both released their respective updated Heavy Duty body styles, while horsepower and torque stayed the same, the max tow capacity shot up massively.

Other extremely convenient changes occurred for the L5P Duramax in 2020, including a relocated DEF tank fill location and new bed steps for accessing the front of your truck bed. 

Uncrackable ECM/TCM

The ECM used in the new L5P Duramax trucks is very complex, this is rather obvious. It really took years for these trucks to be tuned, and they had the downside of being unlike other diesel trucks in that there were no plug-and-play options.

Adding custom tunes to your L5P Duramax meant that the ECM and TCM had to be swapped with a modified version that is capable of receiving tuners.

Currently, HP Tuners are the only software available that you can effectively use to tune the trucks once you have swapped the ECM. Many companies are creating the tunes themselves, and emissions-present tuning has achieved up to 600 horsepower. 

However, while these numbers are appealing and are enough to make your mouth water, the prices of custom tuning and an ECM/ TCM swap can take a lot of money right out of your wallet. 

L5P Tuning Options

If you want to increase the power of your L5P without turning to the custom tuning you can turn to a few options to do so.

There are options with the ‘Banks L5P derringer’ which you can get without even having to remove and replace your ECM and TCM. 

Which at around half a thousand dollars you could make up to 61 additional horsepower if you think it is worth it, it will also provide you with an additional 112lb-ft of torque. 

Banks are a good option as their products are always thoroughly tested before they are publicly released. 

You can also get the option of the ‘Edge Pulsar’. This option is good, they do claim to provide gains of up to 90 horsepower and 156 lb-ft of torque.

It is even easier to install, simply plugging into the ECM, it can be hard to do as a one-man job, however, if you have someone who is s mechanically savvy as you it can be done, or you could take it to a shop and get it done in a shop as an option as well. 

The Major Changes of 2020. 

In 2020, so many things changed for the L5P Duramax, GM made many major steps and changes to the technical aspects of their trucks Both of the 2020 GMC Sierra HD and the Silverado HHD models have the additions of over 15b new camera views, trailer technology, and an available power take-off option.

These heavy duty trucks are larger in every aspect of the 2020 model. They are longer, tall, and much more spacious than their predecessors. Their cabs have gained an additional 3 inches of legroom as well, so you can really stretch your legs. 

What do we love though? The best change that GM made in 2020, is the Durabed truck box… let's look into that some more.

The L5P Duramax Durabed Specs 

One of the most useful changes GM made in 2020 was the new DUrabed model. The new GM heavy duty trucks will have an increased bed length of 6’9” on a standard bed and will retain an 8’ long bed configuration.

Both the larger and the standard bed will gain box length and maximum box volume too. It will make cargo easier to lift into the bed as box lift-in height and overall height has been decreased. 

It offered up to 12 tow-hooks in the bed for your use to secure your cargo. You can also get an optional 120 volt power outlet which is available for all bed applications. 

This option also has other features such as new side-panel bed steps, which are capable of supporting 500 lbs, corner steps integrated into the rear bumper, and a power up/down tailgate which is available on the higher trim models. 

We have more specifications regarding the new Durabed for you below. 





Box Floor Length:

97.8 inches

98.3 inches

Box Height:

21.2 inches

21 inches

Box Width Between

Wheel Housings:

51 inches

50.6 inches

Maximum Box Volume:

76.4 cu. feet

83.5 cu. feet

Box Lift-in Height:

39.6 inches

38.8 inches





Box Floor Length:

78.8 inches

82.2 inches

Box Height:

21.1 inches

21 inches

Box Width Between

Wheel Housings:

51 inches

51.9 inches

Max Box Volume:

61 cu. feet

69.6 cu feet

Box Lift-in Height:

39.8 inches

38.9 inches

L5P Towing Capacity

The L5P Duramax has an impressive towing capacity, with 445 horsepower and 910 lb/ft of torque, it will tow pretty much whatever you throw at it. However, the towing capacity isn’t the same throughout the model years. However, you may see that Chevrolet made adjustments throughout the years that improve the total towing capacity. 

  • The 2017-2019 Chevrolet HD and GMC HD trucks have a max towing capacity of 23,300lbs
  • In 2020, the GM engineers overhauled the trucks and increased the capacity by 52%. So they then had a towing capacity of 35,500lbs. 
  • In 2021, they made slight revisions and improved the maximum towing capacity some more, up to 36,000lbvs