L5P Duramax Specs & Engine Information You Need to Know

If your life demands a diesel engine that combines brute-force towing capability with modern refinement and proven durability, look no further than the GM L5P Duramax.

Since its 2017 debut, this 6.6L V-8 turbo-diesel has set a new benchmark for heavy-duty powertrains, engineered from the ground up for those who rely on their truck for more than just weekend appearances.

This isn't just an evolution; it's a significant leap in power, technology, and real-world reliability.

The L5P Duramax offers 470 horsepower at 2,800 RPM and 975 lb-ft of torque at 1,600 RPM in 2024 models. It has a 6.6L V8 setup. Bore is 95 mm. Stroke is 110 mm. The compression ratio is 16.0:1.

This indicated that the 6.6 L5P Duramax was strong, high-torque, and much less temperamental than some previous high-output diesels.

Read on. I share L5P Duramax specs, year-by-year hp & torque, towing capacity, common issues, and practical maintenance tips below.

L5P Duramax Engine Overview

The L5P is a 6.6L turbo-diesel V8 from GM. It started in 2017. It runs in heavy-duty trucks. Key feature is dual injection. It boosts efficiency.

L5P Duramax is essentially a 6.6L V-8 diesel engine that was designed to be used in heavy service.

It is a 90-degree V-8 featuring a cast-iron block and aluminum heads, which is built with torque first and horsepower second, since in the towing world, torque is what bills.

It was introduced into Silverado HD and Sierra HD trucks and cab-chassis models and soon became the standard of contemporary GM diesels.

Technical Specs on 2017+ L5P Duramax

Core 6.6 L5P Duramax specs include 6.6L displacement. V8 setup. Bore 95 mm. Stroke 110 mm. Compression 16:1. Fuel system evolved from CP4 to CP3.

These are the hardware and performance numbers that matter when you compare engines or pick a truck.

L5P Duramax Core Specs

• Displacement: 6.6 L (6,597 cc).
• Configuration: V-8 engine, 90° bank angle
• Bore x Stroke: 95 mm × 110 mm
• Compression Ratio: 16.0:1
• Block and heads: aluminum cylinder heads made of cast iron block.
• Valvetrain Pushrod OHV, 4 per cylinder.
• Fuel system: CP4.2 high-pressure pump→ CP3 retrofit program
• Turbo: variable geometry turbocharger (VGT) that is optimized regarding spool and high flow capability.

Source: GM Media Archive

Note: This long-stroke design prioritizes torque production at low RPMs, which is essential for moving heavy loads from a standstill.

Duramax engine specs by year; this is the part most buyers obsess over: how much power and what it translates to in real towing numbers.

Performance Output: Horsepower & Torque (Stock)

• 2017-2023 L5P: 445 hp @ ~2,800 rpm, 910 lb-ft @ ~1,600 rpm. (According to GM's official ratings)
• 2024+ L5P Refresh: 470 hp @ ~2,800 rpm, 975 lb-ft @ ~1,600 rpm. (GM engineers revised the turbo and fuel flow on the refresh to extract more power)

According to GM's published specifications.

The entire idea here has to do with torque at low RPM; you want high twist at 1,500-1,800 rpm when towing heavy trailers.

Transmissions Usually Paired With

Some will be heavy-duty Allison automatics, early combinations with 6-speed types, and later switches to 10-speed Allison boxes to better take the load and the spread ratios to towing.

The official rating changes are manufactured through tweaks (turbo, injector flow rate, emissions calibrations) over the years.

When shopping, always check the exact model year, and truck spec ratings can change slightly by cab/axle/transmission setup.

L5P Engine Components & Upgrades

Fuel system delivers high pressure. Turbo boosts air. Emissions handle exhaust.

Knowing what's under the hood helps when you maintain, modify, or troubleshoot.

1. Fuel Delivery and Combustion

The L5P uses a high-pressure common-rail fuel system (29,000 psi) with modern Denso hardware (HP4 family on many L5Ps). This is built to deliver extremely high injection pressures with Bosch piezoelectric injectors for cleaner, more efficient combustion and more power.

The system's precision + redesigned piston/cylinder head bowls = better swirl, better mixing, and cleaner burn.

2. Turbocharger and Air Intake Enhancements

The L5P employs a variable-geometry turbo (VGT): originally BorgWarner/B2BV variants, designed to give quick spool and high flow when needed.

Later model updates increased flow and refined vane control to reduce surging and broaden usable torque. Intercooler and intake plumbing were also revised in refreshes to reduce intake temps and improve transient response.

3. Emissions and Aftertreatment Package

The new L5P diesels are not only the engine block: the aftertreatment package is essential:

• DOC (diesel oxidation catalyst), DPF (diesel particulate filter), and SCR (selective catalytic reduction).
• DEF(diesel exhaust fluid/urea) is needed: check the quality and quantity.
• Regeneration strategies (passive and active) are automatic but require owner awareness: ignore DPF warnings and you'll end up with downtime and expensive fixes.

4. Common Owner Upgrades

Many experienced owners and builders recommend the engine upgrades.

• Secondary lift pumps for extra fuel safety under modified tunes.
• Better intake piping and intercooler tweaks for cooler charge temps when towing.
• Tunes that keep emissions systems intact (non-delete) for legal, road-friendly power gains.
• Upgraded turbo hardware for serious towing or commercial use.

CP4 Pump Concern (2017-2020 models):

The CP4.2 high-pressure fuel pump used in early L5Ps gained a reputation in the diesel community for being susceptible to failure, particularly with contaminated fuel. (Widely reported in industry publications and owner forums)

This underscores the critical importance of using high-quality fuel and changing filters diligently.

It's worth noting that subsequent production revisions and the move toward Denso HP4 hardware in later models aimed to improve fuel system robustness.

If you're looking for Duramax diesel engine specs for modification planning, always match hardware changes to the fuel system and transmission capacity: power without drivetrain support is just expensive drama.

L5P Duramax Towing & Payload Capacity

Max towing reaches 36,000 lbs gooseneck. Payload up to 7,442 lbs.

Towing capacity is determined by axle, cab, frame, hitch, and GCWR, and therefore, there are quite a few variations:

Max Towing:

• Regular Cab DRW: Up to 36,000 lbs (gooseneck)
• Crew Cab SRW: ~23,000 lbs (depending on axle ratio)
• Payload: ~7,442 lbs (depending on configuration)

Note: The manufacturer's tow charts are the last word. Always consult your specific vehicle's GM trailering guide (available online via your VIN) for the definitive rating, as it varies significantly with configuration.

As the Duramax L5P diesel engine specs are often swapped when buying used trucks, know that the same type of engines on the same year of model may be different in the amount of pounds that it can pull, depending on the type of truck (2500/3500, SRW/DRW), type of cab, and hitch prep.

Real-World L5P Duramax Fuel Economy and Performance

Highway 18-22 MPG. City 14-17 MPG. Towing drops.

If you buy an L5P Duramax expecting car-like economy, cool your jets. It is not an eco-compact, but a powerful diesel.

• Highway (light bearing): Most owners note around 18-22 mpg in the 3/4-ton trucks when not hauling heavy loads.
• City/stop-start :~14-17 mpg, diesels are less efficient when you're constantly idling or crawling.
• Towing heavy: expect a meaningful drop, sometimes a 20-40% hit depending on trailer weight and aerodynamics.

The real-world economy is massively impacted by box weight, trailer aerodynamics, gearing, and operator behavior. Keep RPMs lower when cruising, maintain proper tire pressures, and don’t lug the engine

That’s why the 6.6 L5P Duramax specs contribute to impressive fuel efficiency for a heavy-duty truck.

L5P Common Problems & Reliability Insights

No engine is perfect. CP4 failure in early models. EGR leaks. Turbo surge.

Here's what owners commonly talk about on Duramax forums and what to watch for.

Frequent or Notable Issues

• CP4 Pump Failure (2017–2020 models): Some pump hardware (CP4 lineage or early HPFP variants on other Duramax generations) gained notoriety in the diesel world; L5P moved toward Denso HP4 hardware to address earlier failure modes, but fuel system health remains a critical area to monitor (contamination, filter changes, etc.).
• Turbo Surging: Early units had transient turbo behavior that GM revised in later years with stronger vanes and recalibration. Post-2020 hardware tweaks improved this.
• Injector harness chafing/sensor wear: As with many modern diesels, wiring harnesses and sensor mounts can be stress points that benefit from visual inspection during service.

Durability Summary

When cared for, L5P Duramax engines are durable.

Oil changes, swapping of fuel filters, maintenance of DEF and DPF systems, and a lot of care are what can make the difference between driving the truck to 300k+ miles and spending more time in the shop than in the driveway.

When you are intending to purchase used, ensure you receive an extensive service history and a pre-purchase inspection with keen interest in the fuel system and turbo components.

L5P Duramax Maintenance Tips

Change oil regular. Check harness. Lube linkages.

Simple practices keep complex engines from turning into money pits.

1. Stick to oil schedules. Diesel synthetic oil, the correct grade, and timely changes preserve the turbo and bearings. If you tow for work, shorten intervals.
2. Change fuel filters regularly. Contaminated fuel is the fastest way to cause injector and high-pressure pump failure. Use quality filters.
3. DEF & aftertreatment care: Keep DEF topped and use a quality product; contaminated DEF can cause headaches. Check regens cycles and do not disregard the warnings of DPF/SCR.
4. Visual checks: Check injection in harness routing, turbo actuator linkage, and fuel lines to ensure no chafing or loose clamp is present - find small wear before it occurs as a failure.
5. Cooling & intake health. Keep intercoolers clear and keep radiator/cooling circuits clean - excessive heat is an undesirable development in the diesel of the day.
6. Professional diagnostics. If a major code shows up, get it read professionally. Don't wait for emissions or fuel system fault codes.
7. Use OEM or Equivalent Quality Fluids and Filters: Don't compromise on the quality of engine oil, DEF, and filters. Using parts that meet GM's specifications is a cheap insurance policy for your expensive engine.

From owner reports, the single most effective habit is changing fuel filters regularly with quality brands.

Following these steps makes the Duramax L5P specs mean more than just numbers -- they mean the engine actually hits those numbers for years.

Comparison: L5P vs. Older Duramax Variants

For those familiar with the Duramax lineage (LB7 → LBZ → LMM → LML → L5P), the L5P isn't just another step; it's a generational leap.

Old Duramax lacked punch. L5P outshines. More HP. Better tech.

Engine	HP @ RPM	Torque @ RPM	Compression	Injection Pressure
LBZ	360 hp @ 3,200	650 lb-ft @ 1,600	17.5:1	123,000 psi
LMM	397 hp @ 3,000	765 lb-ft @ 1,600	16.8:1	126,000 psi
LML	397 hp @ 3,000	765 lb-ft @ 1,600	16.8:1	129,000 psi
L5P	445 hp @ 2,800	910 lb-ft @ 1,600	16.0:1	129,000 psi

While earlier models like the revered LBZ are known for their simplicity and ruggedness, the L5P was designed to deliver modern performance while meeting stringent emissions standards, without sacrificing durability.

Here's the short take:

• LBZ/LB7 era: earlier technology, lower HP/TQ, simpler emissions. Rugged but less refined.
• LMM & LML: incremental jumps in injection pressure and emissions tech; LML introduced more complex emissions hardware.
• L5P: significant step forward: stronger block, modern high-pressure injection, refined turbo control, and higher stock torque and horsepower.

In plain speak, L5P is the one for people who want modern power and towing ability without losing the durability of earlier Duramax blocks. It's the practical evolution rather than a radical experiment.

Matching the Duramax L5P Specs to Your Lifestyle

The possession of L5P Duramax is not only a matter of bragging but also a matter of choices. After you clear the 6.6 L5P Duramax specs (horsepower, torque), most of the everyday reality lies in the way you will be using the truck and in the little choices that you make during the initial stages.

The same engines can be put into two trucks and seem completely different based on tires, gearing, and towing habits, and even such simple aspects as oil brand and the frequency with which the owner checks DEF. Then, as you look at one, do not look at peak torque, but look at lifestyle fit.

Light Duty vs. Heavy Work

When you make most of your money moving a boat on the weekends, you will have a very different maintenance requirement and adjustment route than someone who makes a living moving a trailer with a 20k-lb load on it 5 days a week.

Light-weight tower drivers will appreciate the fuel economy and comfort; commercial users of heavy-weight use live and die by cooling, transmission robustness, and reliable service periodicities.

The difference must inform your purchasing decision of whether you choose heavyweight towing packages, upgraded brakes, or a higher-strength rear axle.

The Smart Way to Modify an L5P

Aftermarket reality check. The Duramax L5P specs make it have a healthy aftermarket, which is great, but it's also why you'll see trucks with wildly different reliability stories. Upgrades like better intercoolers, secondary lift pumps, and reinforced turbo housings can be smart investments, especially if you plan to tune.

However, do not get into the trap of cheap power: a song that increases the numbers without corresponding fuel, cooling, and other spheres of the vehicle improvements will make life shorter and result in costly failures.

Incremental is the smart way: filtration and cooling, then intake/exhaust, only then the conservative tune, which does not push the limits of emissions hardware.

Don't Ignore Software and Dealer Updates

Software and updates are underrated. Modern diesels are as much software as metal. Dealer updates and calibrations can quietly improve driveability and longevity.

If you buy used, ask whether the truck has received recall fixes and software updates. A one-hour dealer visit can sometimes fix quirks that a thousand miles of trial-and-error won't. It's low-effort, low-cost insurance.

Everyday Driving Habits That Make a Difference

Actually helpful tips to take into consideration when driving a car daily: maintain consistent speeds on the highway, avoid straining the engine by lingering in low gears, and attempt to avoid sustained steep climbs at constantly high RPM rates.

Aerodynamic considerations (caps, tailgate position on some trailers) and the correct tire pressure can save an unexpected amount of fuel. In addition, during towing, you should also keep pace with the traffic; abrupt acceleration and braking consume a lot of fuel rather than constant 60-65 mph.

Keeping Resale Value High

The L5P name carries weight in the market. Trucks with documented service history, OEM parts, and conservative mods command a premium.

Buyers notice care: fresh oil records, proper DEF receipts, and clean DPF logs tell a story. Conversely, trucks with harsh tunes and a history of deleted emissions gear are red flags; they scare off many buyers and can tank resale value.

The Power of the L5P Community

Lastly, community matters. There is an active owner scene of the L5P: forums, Facebook groups, and stand-alone shops specialized in Duramax work. These groups are gold in troubleshooting, sourcing parts, and learning best practice maintenance practices.

They are useful; however, not all postings on the forums should be taken as the law of Moses. Check the technical support information and favor written solutions over speculation.

FAQs

Q: What year did Duramax get DEF?

A: Diesel Exhaust Fluid (DEF) was first introduced on the Duramax with the LML engine, starting in the 2011 model year. This was part of a broader industry shift to Selective Catalytic Reduction (SCR) technology to meet stricter EPA emissions standards.

The L5P, from its 2017 introduction, continued and refined this DEF/SCR system.

Q: What oil should I use in an L5P?

A: Always use a diesel-rated synthetic oil that meets GM's latest specification, which is typically dexosD™. This information is clearly stated in your owner's manual.

Using the correct oil is non-negotiable for protecting your turbocharger and emission system. For severe service (like frequent towing), most experts recommend shortening the change interval by 25-50%.

Q: Can I tune the L5P without deleting emissions gear?

A: Yes, "emissions-on" or "green" tuning is a popular and legal option. Reputable tuners offer calibrations that provide significant power gains while keeping the Diesel Particulate Filter (DPF) and SCR system fully functional and intact.

It is crucial to understand that even with emissions intact, aggressive tuning can increase stress on the transmission and fuel system, so supporting modifications may be advisable

Q: What's the difference between LML and L5P?

A: The L5P has stronger internals, a more robust block, improved injection hardware, and updated turbo control, resulting in more torque and generally improved durability.

Beyond the obvious power jump (910 lb-ft vs. 765 lb-ft), the L5P feels fundamentally more robust. Key differences include:

• Fuel System: The L5P's (post-2020) Denso HP4-based system is considered more robust than the LML's CP4.2 pump.
• Engine Block: The L5P features a stronger, more rigid block designed to handle its higher output.
• Turbocharger: The L5P's variable-geometry turbo is larger and more sophisticated, providing better response and peak flow.

The L5P is the more capable, durable, and modern engine out of the box.

Q: Does the L5P have a factory lift pump?

A: The L5P does have a sophisticated factory fuel supply system. However, it does not include a dedicated, high-flow mechanical lift pump between the tank and the high-pressure pump.

For this reason, many owners choose to install an aftermarket lift pump as a first and highly recommended upgrade.

This provides an extra layer of protection against fuel contamination and ensures a steady supply of fuel to the high-pressure pump, especially under high load or with performance tunes.

Conclusion: Should You Pick the L5P Duramax?

L5P Duramax delivers strong power and reliability. It suits towing and daily use. I recommend it for truck owners.

The L5P Duramax is a clever choice to buy in case towing, hauling, or simply wanting a modern-built and tough diesel are some of the elements of your life.

It gives you:

• Massive low-end torque that makes towing feel easier,
• A durable foundation (cast iron block, modern internals),
• Modern Duramax diesel specifications that balance emissions with performance, and
• Well-established post-sales support and upgrade infrastructure.

The 2017-2023 models provide 445 hp/910 lb-ft, but 2024+ raises it to 470 hp/975 lb-ft - actual figures, which translate to actual towing capability when optimally set up.

Maintenance practice, with respect to the fuel system, and the L5P Duramax specs will return you a long and productive life.

About the Author- John Barrett

More Reading

• L5P Reliability
• GM Official Towing Guides Website
• SAE International Papers on Diesel Engine Evolution