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

6.6L L5P Duramax Specifications, Information, and Resources!

2017+ Chevy HD & GMC HD Diesel trucks

GM’s 6.6L L5P Duramax joined the ranks of Chevrolet Silverado HD and GMC Sierra HD trucks in 2017. While the trucks’ exteriors looked very similar to the LML Duramax, with exception to the newly found hood-scoop, the L5P diesel engine hardly resembles the old LML at all. In fact, the displacement is practically all it share in common with the LML. The 6.6L L5P Duramax engine posts significantly better performance specs, towing ratings, and even reliability. So what changes took place to make the L5P Duramax engine more powerful, capable, and reliable than previous generations of the Duramax?

We’ll go over all these factors in this post, our comprehensive guide to the 6.6L L5P Duramax Diesel. Let’s dive in.

2020 Chevrolet Silverado 2500HD with the 6.6L L5P Duramax Diesel engine.
2020 Chevrolet Silverado 2500HD with the 6.6L L5P Duramax engine.

Engine Design

6.6L L5P Duramax Diesel Engine
2017 L5P Duramax Diesel Engine pictured above. Photo taken from Chevrolet Media Website.

Similar to engine designs in the past, the L5P Duramax engine utilizes a 90-Degree V-8 configuration. The block is cast-iron for superior strength, with induction-hardened cylinder walls and five nodular main bearings for even greater durability. The L5P’s engine block features a deep-skirt design, that has four-bolt, cross-belted main caps. This helps bolster the engine block and also enables more accurate location of the rotating assembly.

The die-cast aluminum lower crankcase further strengthens the engine block, while simultaneously acting as the lower engine cover. This helped GM achieve some weight savings too. Significantly bigger Crankshaft rod journals, when compared to the LML, are allow the use of a stronger crankshaft and more bearing area to sustain higher cylinder loads. These rod journals are cut-then-rolled, strengthening the journal-web connection. The crankshaft itself is made of forged micro-alloy steel.

The connecting rods are forged with a powdered steel alloy, with a fractured cap design. They use a 45-degree split-angle design. This allows larger diameter rod bearings to pass through the cylinder bores during assembly.

6.6L L5P Duramax Engine Components Compared to 6.6L LML Duramax
L5P Duramax Vs LML Duramax

Cylinder Head Design

Aluminum cylinder heads are still used in the L5P, just like earlier Duramax generations. Six head bolts provide significant head-clamping strength. Four valves are found per cylinder. The casting of the aluminum head uses a new, double-layer water core design. This design arranges the water cores in layers. The result is a stronger cylinder head structure with better coolant flowing properties. Airflow passages were also revised to improve airflow, helping to increase performance.

Stronger Pistons

The L5P’s revised piston design results in significantly greater durability. These new cast-aluminum pistons have a taller crown area, and a remelted combustion bowl rim. Remelting is a process in that extends life and improves durability. After the pistons are cast, the bowl area is reheated. This creates a finer metal grain structure that can be attributed to longer lifespans. The pistons also don’t use pin bushings, reducing weight and improving performance.

Other Notable L5P Duramax Engine Features

GM’s engineers adding a better lubrication system and oiling circuit to help make sure this engine can hold up to its high performance numbers. The enhanced oiling circuit offers higher flow and a dedicated turbocharger feed. This provides faster oil delivery and increased pressure at the turbocharger. Piston-cooling jets at the bottom of the cylinder bores were upsized to provide twice the amount of engine oil to the piston crowns. This further helps lower engine temperatures and increase reliability. An integrated oil cooler is also present on the L5P that offers 50% more capacity than that of the LML engine’s.

The L5P utilizes a new two-piece oil pan for greater NVH reduction and durability. The bottom piece is made of laminated steel and helps reduce and vibration. The top piece offers greater rigidity.

L5P Duramax Performance Specs

The new L5P Duramax is by far, the most capable duramax to date, producing 445 horsepower and 910 lb-ft of torque in stock form. Similar to the LML, the L5P utilizes the same 6.6L displacement. The engine itself is vastly different however, with numerous big changes that resulted in an increase in 48 horsepower and 145 lb/ft of torque over its LML predecessor. Changes included a Borgwerner Variable Geometry Turbocharger, a fuel system overhaul, and a fully-functional hood scoop intake system. There are a lot of other features that help make the L5P Duramax as impressive as it is too. We’ll go into detail about how these performance attributes and their contributions below.

6.6L L5P Duramax Performance Specs
L5P Duramax Performance Specs

Borgwerner Variable Geometry Turbocharger

The L5P Duramax utilizes a variable geometry turbocharger supplied by Borgwerner that is electrically actuated and electronically controlled. Traditionally, Duramax trucks have been equipped with Garrett units so this is a big shift! This BW variable vane turbocharger utilizes a billet compressor wheel with 11 blades and has a slightly larger inducer than previous Duramax generations. Maximum boost pressure is increased over the LML, to 28 psi in order to provide better performance. This turbocharger also acts as an exhaust brake, similar to the one found on the LML, just better.

The L5P’s turbocharger was revised to provide greater exhaust braking capabilities. Internal leakage was reduced, allowing more exhaust energy to be captured during exhaust braking. The factory exhaust brake system creates peace of mind while towing by adding back pressure in the exhaust system, slowing the vehicle down during deceleration and down-hill driving. If you tow, this is a must-use feature because it’ll significantly extend brake pad life and make big trailers much easier to manage especially when driving in mountains or other unfriendly terrains.

Fuel System Overhaul

The L5P Duramax uses a common rail direct-injection fuel system. Unlike fuel systems in the past, even as recently as the LML, this fuel system isn’t supplied by Bosch. The entire system is made by Denso. The fuel system operates at 29,000 psi, or 2,000 bar, which helps provide a cleaner fuel burn to reduce emissions and better overall performance.

Denso HP4 Injection Pump

The Injection Pump chosen for the L5P is Denso’s HP4. This injection pump is drastically different than the Bosch units found on older trucks. It has three high-pressure cylinders, a filter screen that catches debris/particles at the pump’s inlet, and it’s supplied a steady stream of fuel from the first in-tank lift pump found on a factory Duramax. That’s right, the L5P Duramax comes from the factory with a built-in lift pump. This improves longevity of the injection pump because it takes a significant work load off of it. On previous engines, the injection pump would have to both pressurize fuel for the injectors and siphon fuel from the tank. This was in-efficient and often caused problems on trucks with any sort of performance modifications.

Denso G4S Gen 3 Injectors

The L5P Duramax’s injectors are solenoid injectors, instead of piezoelectric ones like those that are found on the LML Duramax. These injectors are less complex, but because of their advanced technology, they offer performance similar to piezo-style units. These Denso G4S Gen III injectors can support up to seven fuel delivery events per combustion cycle. This gives the L5P lower NVH, while simultaneously providing greater efficiency and cleaner emissions.

New Intake System

A fully-functioning hood scoop was added to GM Heavy Duty trucks to accompany the L5P Duramax engine. It’s one of the few visible differentiators between late model LML trucks and newer L5P ones.

Another critical element of the L5P Duramax’s impressive performance specs is a brand new intake system. GM incorporated a hood scoop, as pictured above, to provide more cool, dense air to the engine. Cooler air has greater density which results in better combustion. This improves power, reliability, fuel economy, and reduces emissions. It also helps keep the engine cooler, especially while under heavy load or difficult conditions. Adding a fully functional hood scoop provides constant cooler air because it provides air derived away from the engine. It also provides dramatically more air than just your normal intake system.

In fact, this hood scoop provides 60% of the air to these Duramax engines. The air filter housing draws the other 40% of air from a dry location in the front fenders. Before air from the air filter housing enters the combustion chamber, it mixes with the cooler air from the hood inlet. Drawing air from different locations guarantees that even if one is blocked, the other can still adequately supply cool air to support the engine.

Safety First

GM took special precautions to make sure the air received by the new intake system stays clean and dry too. An air/water separator mechanism exists within the system. It works like this: air enters an expansion chamber that contains a very sharp 180-degree turn when en route to the air filter housing. This sharp turn creates a velocity change where any moisture or humidity forms larger droplets that are then flung against the outside housing wall, where it then drains through a valve. Take a look at one of their testing photos where they put the L5P Duramax through a number of worst-case scenarios down below.

6.6L L5P Duramax Air Intake Testing
Air intake testing done on 2017 L5P Duramax trucks.

Allison Transmission

6 Speed Automatic Allison Transmission
6-Speed Automatic Allison Transmission

The Allison Transmission is one of the most important features of Duramax trucks. Plenty of people consider these transmissions the most durable of all heavy duty diesel trucks. The L5P Duramax utilizes a 6-speed Allison Transmission from 2017 to 2019. In 2020, a 10-speed Automatic Allison Transmission replaces the old 6-speed.

The 10-Speed Allison Transmission puts power to the ground better than the previous 6-speed unit. It puts more torque down in lower gears, resulting in smoother and shorter shifts. It also provides greater performance, putting all 910 lb-ft of torque to the ground in first gear. This transmission also enables smart engine braking to extend brake pad life. Another useful feature is that this Allison tranny eliminates the need for an aftermarket PTO or Power Take Off Unit. The 10-speed Allison features an integrated, chain-driven PTO system, capable of powering equipment at job sites by clicking a button in the cab.

6.6L L5P Duramax Engine Specs

For a full breakdown of the 6.6L L5P Duramax specs that make these engines so capable, see the chart below.

Manufactured Years:2017-2021
Engine Design:90-Degree V8 Turbocharged Diesel
Transmission:2017-2019: Allison 1000 6-Speed Automatic
2020+: Allison 10L1000 10-Speed Automatic
Displacement:
6.6 Liters or 403 Cubic Inches
Bore:4.055″ or 103 mm
Stroke:3.897″ or 99 mm
Block Material:Cast Iron
Cylinder Head
Material:
Cast Aluminum
Intake Manifold:Cast Nodular Iron
Crankshaft:Forged Steel
Camshaft:Steel
Connecting Rods:Iron
Compression Ratio:16.0:1
Firing Order:1-2-7-8-4-5-6-3
Turbocharger/Air:BorgWarner Variable Geometry Turbocharger
(VGT)
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
Valvetrain:32 Valve (4 Valves per cylinder) OHV or Overhead
Valve
Engine Oil Capacity:10 quarts or 9.5 Liters
DEF Fluid Capacity:7 Gallons
Cooling System
Capacity:
31.4 Quarts or 29.72 Liters
Fuel:B20 Biodiesel Blend or Ultra Low Sulfur Diesel
Fuel Tank Size:36 Gallons Standard
Max Engine Speed:3,450 RPM
Max Braking Speed:4800 RPM
Horsepower:445 Horsepower At 2800 RPM
Torque:910 lb/ft at 1600 RPM

L5P Duramax History & Model Year Changes

In 2017, the L5P Duramax Diesel engine is introduced on GMC and Chevy HD

2017 : L5P Duramax Introduced

In 2017, the 6.6L V-8 L5P Duramax Diesel engine is introduced on Chevy HD and GMC HD trucks. The new L5P is the most capable Duramax thus far offering 445 horsepower @2,800 rpm and 910 lb-ft of torque at 1,600 rpm.

2018 L5P Duramax Denali HD Improvements over 2017

2018: Minor Styling & Tech Improvements

  • New Colors Added
  • 7″ My Link Display Standard on base models
  • New Denali grille Design (GMC only)
  • New High Country and Z71 grille design (Chevy only)
  • Tire pressure alert added on TPMS system
  • Rear-view camera standard on all models with cargo box
2019 GMC Sierra HD

2019: Calm Before the Storm

No significant changes were made to 2019 models. We suspect this is due to the sweeping changes that will be made on 2020 Chevy HD and GMC HD trucks.

2020 Sierra HD with the L5P Duramax Engine

2020: Massive Reform

2020 Chevy HD and GMC HD trucks were overhauled. A new body-style is added, new towing technology and features are available and the L5P Duramax is updated to help support a new max tow capacity of 35,500 lbs. That’s a 50% increase over 2019 models. A 10-speed Automatic Allison Transmission replaces the 6-speed unit found on older L5P variants. A 6.6L Gas engine is introduced.

2021: Tech & Trim Refinement

  • Carhartt Special Edition Added (Chevy Only)
  • Wireless Apple CarPlay and Android Auto Added
  • Bed View Camera available on WT, Custom, and LT models.
  • EZ Lift Tailgate available on LT models
  • Safety Confidence Package available on WT and Custom models

Between 2017 and 2019, the GM Heavy Duty trucks equipped with the L5P Duramax engine look almost identical to the LML Duramax. The main way to differentiate the two trucks by only looking at the exterior is by the hood scoop. In 2020, Chevrolet and GMC both released their respective updated Heavy Duty body styles. While the horsepower and torque numbers remained the same, max tow capacity was increased tremendously. Other convenient changes to the L5P Duramax in 2020 including a relocated DEF tank and DEF fill location and new bed steps to access the front of your truck bed.

L5P Duramax Uncrackable ECM/TCM

One thing that was clear almost immediately was the complexity of the ECM used in the new L5P Duramax trucks. It took literally multiple years for the trucks to be tuned and unlike other diesel trucks, there are no plug-and-play options. To add custom tunes to your L5P Duramax, the ECM and TCM have to be swapped with a modified version capable of receiving tuners. At this moment, HP Tuners is the only available software that can be used to tune the trucks after an ECM swap. Multiple companies are creating the tunes themselves, and up to 600 horsepower is being achieved on emissions-present tuning! While the numbers are really impressive, so is the price. Custom tuning and an ECM/TCM swap can cost upwards of $5,000.

L5P Tuning Options

If you’re not looking for custom tuning for your L5P Duramax, there are currently a handful of tuning options you can use to increase power on your L5P. You can use the Banks L5P Derringer without removing and replacing your ECM and TCM. At around $500, you can make up to 61 additional horsepower, and 112 lb/ft of torque. As with all Banks products, you can rest assured knowing the products have been tested thoroughly before they are ever released. Another L5P Duramax tuning option is the Edge Pulsar. Edge claims gains of up to 90 horsepower and 156 lb-ft of torque. This option is also much easier to install, simply plugging in to the ECM. It can still be tricky to do by yourself, so have a friend help you or visit a shop and have them do it!

L5P Duramax Changes in 2020

  • Stronger, Cast Iron Block & Improved Cylinder Heads
  • Re-designed reciprocating and rotating assembly
  • New Single-Cooler EGR system that includes integrated bypass
  • New Variable Geometry Turbo capable of 28 psi & Offering improved exhaust braking.
  • Two-piece Oil Pan helps reduce noise and vibration.
  • Integrated Oil Cooler with 50% greater capacity than previous design.
  • Larger diameter crankshaft
  • Solenoid Injectors support seven fuel delivery events per combustion events.
  • Venturi Jet Drain Oil Separator
  • New Ceramic Glow plugs
  • Updated Allison 1000 6-speed Transmission
  • New torque converter

L5P Duramax Changes in 2020

2020 Chevrolet Silverado 2500 HD Custom

Many L5P Duramax specifications were changed GM made major steps to the technology aspects of their trucks in 2020. Both the 2020 GMC Sierra HD and the Silverado HD will be available with over 15 new camera views, new trailering technology, and an available PTO (Power Take Off) option. 2020 GM Heavy Duty trucks will also be larger in every aspect. They’re longer, taller, and more spacious than previous Duramax trucks. Crew Cabs gained an additional three inches of leg-room in crew cab models. Our favorite change GM made in 2020 is the addition of the new DuraBed truck box.

The DuraBed

Perhaps the most useful change GM made in 2020 is the new Durabed. New GM Heavy Duty trucks will have an increased bed length to 6’9″ on standard bed lengths and retain a 8′ long bed configuration. Both the larger, standard bed and the long bed will gain box length and max box volume however. Cargo is easier to lift into the bed as box lift-in height and overall height have been decreased. Up to 12 tow-hooks are available in the bed for your use to secure cargo. An optional 120 volt power outlet is available for all bed applications. Other noteworthy Durabed features include new side-panel bed steps capable of supporting 500 lbs, the corner steps integrated into the rear bumper, and a power up/down tailgate available on higher trim models. For specific L5P Duramax specifications on the new Durabed, take a look at the chart below.

L5P Duramax DuraBed Specifications

8′ Bed

Years:2017-20192020+
Box Floor Length:97.8 inches98.3 inches
Box Height:21.2 inches21 inches
Box Width Between
Wheel Housings:
51 inches50.6 inches
Max Box Volume:76.4 cu. feet83.5 cu. feet
Box Lift-in Height:39.6 inches38.8 inches

Standard 6’9″ Box

Years:2017-20192020
Box Floor Length:78.8 inches82.2 inches
Box Height:21.1 inches21 inches
Box Width Between
Wheel Housings:
51 inches51.9 inches
Max Box Volume:61 cu. feet69.6 cu feet
Box Lift-in Height:39.8 inches38.9 inches

2020 L5P Mechanical Changes Over 2017-2019 Models

  • New 10L1000 10-Speed Automatic Allison Transmission
  • 52% Increase in Max Towing to 35,500 Lbs when properly equipped.
  • Relocated DEF tank and relocated DEF fill location. DEF will no longer be added under the hood. It has been moved to the gas cap.
  • “Beefier” Front & Rear axles.
  • 11.5″ Ring Gears on 2500HD models and 12″ Ring Gears on 3500HD models.
  • 30% Larger Diameter Prop Shafts
  • New 28″ Diameter Variable-Speed Cooling Fan that is 2.5X Larger than previous models.
2020 L5P Duramax Engine
2020 L5P Duramax Engine

L5P Towing Capacity

L5P Duramax Tow Capacity
2020 Chevy HD with L5P Duramax engine towing a trailer. 2020 Chevrolet HD models can tow up to 35,500 lbs when properly equipped! Photo courtesy of Chevrolet Media

With 445 horsepower and 910 lb/ft of torque, the L5P Duramax is capable of towing just about anything you can throw at it. Tow capacity isn’t the same throughout the L5P model years however, as Chevrolet made adjustments throughout the years to improve max tow capacity.

2017-2019 Chevrolet HD and GMC HD trucks with the L5P Duramax have a max tow capacity of 23,300 lbs. In 2020, GM’s engineers overhauled the trucks and increased tow capacity by 52%. 2020 Chevrolet HD and GMC HD trucks with L5P Duramax engines have a max tow capacity of 35,500 lbs. Then, in 2021, slight revisions improved max tow capacity a little more. 2021 Chevy HD/GMC HD trucks have a max tow capacity of 36,000 lbs.

For easy to read L5P Duramax towing specs, we created the chart below to display max towing capacities. Actual tow capacity on your Duramax may differ according to cab configuration, bed length, and whether your truck is 2wd or 4wd. So be sure you check your owner’s manual for exact details on your vehicle.

Year:Max Tow
Capacity:
GCWR:
2017-201923,300 lbs31,300 lbs
202035,500 lbs43,500 lbs
202136,000 lbs44,000 lbs
2017 L5P Duramax Towing

L5P Duramax FAQs

How Much Horsepower And Torque Does The L5P Duramax Have?

The L5P Duramax engine found in 2017+ Chevrolet HD and GMC HD trucks produces 445 horsepower at 2,800 rpm and 910 lb-ft of torque at 1,600 rpm.

What Years Was the L5P Duramax Used in Chevrolet and GMC trucks?

The 6.6L L5P Duramax engine is present in 2017-2021 GM heavy-duty diesel trucks. These trucks include Chevrolet Silverado 2500HD and 3500HD trucks as well as their GMC variants, the GMC Sierra 2500HD and Sierra 3500HD.

How Much Can The L5P Duramax Tow?

Max tow capacity varies amongst years of the L5P Duramax. 2017-2019 L5P Duramax trucks can tow a maximum of 23,300 lbs. 2020 L5P Duramax trucks can tow 52% more than the previous model years for a total of 35,500 lbs. In 2021, tow capacity was increased even further to 36,000 lbs.

Want to learn more about the L5P Duramax?

Check out our other posts about the L5P below!

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ABOUT Kamil

Founder of Diesel Resource and a complete diesel head. Has a little bit of problem buying too many trucks. Learn more about him by checking out his truck.