Released in 2017, the 6.6L Duramax L5P is the latest Chevy & GMC turbo-diesel engine. The L5P produces 445hp and 910lb-ft. of torque from the factory. When dyno’d the L5P produces about 400whp and 850wtq.
You can’t ask for much more power from the factory. However, for those who are looking for some extra power and performance a handful of simple bolt-on performance upgrades can take the L5P past the 550whp and 1,200wtq territory. Getting to and beyond these power levels will require some additional supporting mods which we’ll discuss below. Fortunately, the L5P has a lot less performance inhibitors compared to previous Duramax diesels.
This guide is going to cover the 5 best L5P performance upgrades. Additionally, we’ll cover L5P power limits, and some of the supporting components that need to be upgraded to achieve various power levels. Pushing past the 600whp mark gets very expensive so while we will discuss necessary mods for these power levels, our 5 best upgrades are going to focus on the less expensive and more achievable bolt-on mods.
Duramax L5P Power Limits
Upgrading the L5P is fairly easy, however, there are a few important hurdles to discuss. Fortunately, the L5P has less restrictions and weak points than previous Duramax’s such as the LB7 or LML. We’ll cover these items in a bit more depth below, but here are the biggest considerations:
- The Allison 1000 transmission will need to be built around 550whp, getting it to handle 500whp will require some mods/tuning
- 550whp is pushing the limit on the stock VGT BorgWarner turbo
- The ECM is tough to crack which means tuning options are a bit more limited and expensive
- The stock fueling system can handle 750whp+ (will need larger injectors)
While the ECM is tough to crack, there are still a handful of tuning options we’ll discuss in our best L5P performance upgrades list. Additionally, the stock fuel pump, lift pump, and injectors are surprisingly good for 750whp which saves a lot of money and headache when it comes to modding.
A1000 Transmission Limits
As is true with any Duramax truck, the Allison 1000 transmission in the L5P is the biggest weak point. The stock A1000 runs at 80psi of line pressure which is really low. This impacts it’s ability to hold power and put it to the ground. The transmission can handle 550whp before needing to be built, but you will need to address line pressure prior to this.
At 500whp or anywhere near it we recommend tuning the transmission (TCM tuning) and installing an EPC Solenoid Fooler which will allow the transmission to constantly run over 200psi of line pressure. This will help the A1000 hold power and maintain some reliability at 500whp.
At 550whp, and maybe even a bit before, you’ll need to build out the Allison which will cost about $5,000.
BorgWarner VGT Turbo Limits
The stock L5P turbo is a BorgWarner 61mm variable geometry turbo. At 550whp the turbo is pretty much completely maxed out. I’ve seen some claims of 600whp on the stock turbo, however this would be the absolute limit. Additionally, at those power levels you are at a big risk of blowing the turbo and potential damaging the internals of the engine.
Therefore, we recommend replacing it a 550whp. And if you plan on running a consistent 550whp it is also worth replacing as reliability is questionable at those power levels. Most opt for an upgraded S300-series or S400-series fixed geometry BorgWarned turbo for upgrades.
Best Duramax L5P Performance Upgrades
- ECM Tuning
- Cold air intake
- 5″ exhaust
- Intake horn & resonator pipe
If you would rather consume this content via a video, check out our 5 Best Performance Modifications for the L5P Duramax video below:
1) Duramax L5P Tuning
Engine tuning is the single best L5P performance upgrade. It offers the biggest power gains at the lowest cost per horsepower. However, tuning on the L5P isn’t as simple as hooking up a flash tuner such as SCT. Fortunately, there are still a few options on the market.
The two options are custom tuning or getting a plug-and-play piggyback tuner.This topic is a bit more confusing since the tuners for the L5P aren’t the same as the flash tuners we are used to for pretty much all other diesels. If you are just looking for a bit of extra power get a piggyback tuner. If you need precision and maximum horsepower gains then you need to modify the ECM and go the custom tuning route.
Since the stock ECM is pretty much uncrackable, custom tuning requires you to pull your ECM and send it to HP Tuners for modification. HP Tuners can modify the ECM so that it can then be custom tuned. This service costs about $700 and does not include the tuning. You also have the option to buy a new ECM for $1,500 if you don’t want to send in your ECM.
This is the best option for anyone that needs custom tuning. Unless you are planning on upgrading the turbo and shooting for crazy power levels then you are probably best off opting for a piggyback tuner. Not to mention you will probably end up running $2,000 to $2,500 if you go this route as custom tuning is expensive for the L5P.
L5P Piggyback Tuners
Most diesel tuners you are familiar with, like Edge/SCT/Bully Dog and so on, are flash tuners. They are handheld devices that plug into the OBDII port and allow you to alter the ECU by flashing new maps into it. Piggyback tuners work a bit differently. They connect directly to the ECM, so they don’t come with any handheld devices. Additionally, rather than re-writing or re-flashing the stock tune they instead trick the ECM by adjusting certain signals and sensor readings.
There are a few options on the market like the Banks Power Derringer and the Edge Pulsar module. Both options are around the $800 mark and are simple plug-and-play.
One potential downside to a piggyback tuner is that they don’t offer the ability to do custom tuning. However, most tuners will still come with multiple maps which can easily by changed on the fly via the steering wheel controls.
Piggyback vs. flash tuning is a more complicated topic so check out this article if you want to learn more.
L5P Piggyback Tuner Performance Benefits
- ~100hp gains
- ~150lb-ft. torque gains
- Improved gas mileage
- DME remains stock
- Easy install
- Allows for on-the-fly map changes
2) Duramax L5P Cold Air Intake Upgrade
Upgrading the L5P intake is our second favorite mod since it’s highly complimentary with a tune. Adding an intake with a tune will help maximize power gains from both the tune and the intake. Additionally, it will help reduce stress on the turbo and allow the engine to breathe better.
Tunes increase power from increasing the boost or psi of the turbo. When boost is increase, the intake air is compressed even further. With the air being compressed even further it’s important to bring more air into the intake system as the turbo needs to compress a greater volume of air for the engine. Not only will adding an intake result in some decent power gains, it will also help improve gas mileage, throttle response, and turbo spool.
We prefer open intakes which don’t have enclosed box designs since they flow more air. An open intake will usually increase airflow by about 50% whereas closed systems will provide increases closer to the 30% range. The increased airflow will provide better power gains and less restriction.
If you are in California and aren’t allowed to upgrade your intake, you can instead upgrade the intake resonator piping. This is fully legal in California and reduces the restriction created by the stock intake piping. The stock pipe has a silencer in it which results in significant air restriction.
6.6L L5P Cold Air Intake Performance Benefits
- Up to 20hp and 40tq with a tune
- Better turbo spool
- Quicker throttle response
- 1-2mpg increase
- Cool intake sounds
The power gains quoted are when used in conjunction with a tune. Additionally, these power gains are generally max power gains throughout the power curve and not gains at the peak of the curve. Banks quotes 21whp when combined with their Derringer tune.
Best Upgraded Intakes
3) 6.6L Duramax 5″ Exhaust System
With an intake and tune, we are now flowing a lot more air into the engine. Therefore, we need to increase the outflow of the exhaust air as it leaves the engine. Unfortunately, you can’t install a turbo-back exhaust system without deleting the DPF and SCR systems. You can upgrade the downpipe which we do recommend and will cover later. The next best option to a full turbo-back exhaust is a 5″ DPF-back exhaust system.
A freer exhaust system will reduce exhaust backpressure. Backpressure is bad for turbo diesels. It increase the amount of force against the turbine wheel which impacts the turbo’s ability to spool. This requires the turbo to work harder and overall has a negative impact on turbo reliability. Additionally, it results in higher EGTs.
A larger L5P DPF-back exhaust system will help reduce backpressure and lower EGTs. This results in a healthier and more reliable engine.
Upgrading the downpipe is also highly recommended as it reduces the most exhaust backpressure outside of deleting the emissions systems.
L5P 5″ Exhaust Performance Benefits
- 5-10whp and 10-15wtq gains
- Less exhaust backpressure
- Lower EGTs
- Healthier and more reliable engine and turbo
Reducing EGTs and backpressure is important since both of these items have negative affects on the turbo and its reliability. Adding a tune, intake, and exhaust system will add about 100whp. Considering the turbo is only capable of handling about 550whp it will be getting close to its upper limit with these few mods added. Therefore it’s important to reduce backpressure and lower EGTs as much as possible to help maximize reliability.
4) L5P Intake Horn Upgrade
An intake horn is a common term for the intake manifold. The stock intake horn is plastic and only has a small 2.4″ diameter. Once an upgraded cold air intake is added, the small diameter stock intake horn becomes restricted. Upgrading the intake horn to a 3.5″ diameter steel pipe will increase air flow and therefore increase power.
Wehrli Custom achieved a 25whp gain with their 3.5″ intake horn upgrade, but note this was on an aggressive race tune and heavily modified truck with an upgraded turbo. You can expect about 10whp on a normal tune and lightly modified truck. Their intake horn will fit with any intake system and doesn’t require any additional mods or tuning.
Upgrading the intake horn is a simple, cheap, and effective way to increase air flow and add a solid 10whp to your L5P.
Intake Horn Upgrade Benefits
- Approx. 10whp with a tune and 15-20wtq
- Improved air flow
- Easy bolt-on install
- Looks cool under the hood
5) 6.6L L5P Downpipe Upgrade
Despite putting this last on the list, it’s actually our favorite exhaust upgrade. A big 5″ exhaust system will add good sound, but a downpipe will actually provide better power gains and the most backpressure reduction. A downpipe bolts up directly to the turbocharger and connects with the emissions portion of the exhaust (the diesel oxidation catalyst specifically). Since it bolts to the turbo it has the most impact on backpressure.
The stock downpipe is pretty small and skinny which restricts airflow. Upgrading to a larger 3.5″ downpipe will help improve exhaust flow and therefore reduce backpressure. This will allow the turbo to spool more freely, improving its reliability and increasing power. Additionally, it will have a big impact on lowering EGTs. All of the combined benefits of an upgraded L5P downpipe make it one of the best L5P performance upgrades.
No tuning is required for an upgraded downpipe. Although, as with any mod on this list, adding a piggyback tuner or going the custom tuning route will help amplify the gains achieved. Upgrading the downpipe on a stock L5P will have some small benefits like slightly lower EGTs, but the biggest gains and benefits come when you are running a tune and intake modifications.
L5P Downpipe Upgrade Benefits
- Approx. 10whp and 10-20wtq
- Reduced exhaust backpressure
- Improved turbo reliability
- Lower EGTs
Boosted Performance L5P Downpipe Upgrade
When it comes to Duramax L5P downpipe upgrades, Boosted Performance is leading the charge. The Boosted Performance L5P downpipe bridges a perfect balance between quality and performance. Made from 304 stainless steel, it is one of the strongest downpipes available for the L5P. Its design is centered around exhaust gas temperatures, providing unparalleled efficiency and thermal dynamics. BP’s L5P downpipe was made to provide the best flow figures in the game, utilizing a 3.5” design that meets the perfect balance between velocity and diameter.
Duramax L5P Performance Upgrades Summary
Five bolt-on upgrades can add 100-125whp to a 6.6L L5P Duramax. A stock L5P will dyno around the 400whp and 850wtq range. Adding a tune, cold air intake and horn, exhaust, and downpipe can easily push the L5P into the 500whp and 1,000wtq power range. Fortunately, the L5P doesn’t require many supporting mods as its fuel system can handle in excess of 750whp and the turbo is good for about 550whp.
The one concern with the L5P is the Allison 1000 transmission which is only capable of handling about 500whp. Even if you only plan on adding a tune we’d recommend doing the EPC Solenoid Fooler mod and getting TCM tuning to improve transmission reliability. If you plan on upgrading the turbo, you’ll need to build out the Allison transmission and get custom ECM tuning.
If you’re looking to keep things on a budget and want to aim for slightly more power and better MPG, then drop a Derringer tune and cold air intake on the L5P. For the majority of performance folks this will be enough. If you keep it on a modest tune you shouldn’t have any issues with the A1000 transmission.
What mods are you running on your 6.6L L5P Duramax?
Stock turbos, stock injectors, and internals can easily handle 600 horsepower, which means that the Allison 1000 will give up the ghost without substantial upgrades.How do I get more power from my L5P? ›
Adding a tune, cold air intake and horn, exhaust, and downpipe can easily push the L5P into the 500whp and 1,000wtq power range. Fortunately, the L5P doesn't require many supporting mods as its fuel system can handle in excess of 750whp and the turbo is good for about 550whp.How much HP does a tuned L5P make? ›
While the rated output for the L5P is 445 HP and 910 ft-lbs of torque it dyno'd 405 Rear Wheel Horsepower (RWHP) and 850 ft-lbs on our loaded chassis dyno.What is the best Duramax for tuning? ›
The LBZ also offers excellent tuning and modification potential, which is extremely attractive to most diesel enthusiasts. Finally, the LBZ is the last generation of Duramax without emissions control parts, which gives it superior reliability. For those reasons, the LBZ is our choice for the best Duramax engine.What is the max HP for a L5P Duramax? ›
L5P Towing Capacity
With 445 horsepower and 910 lb/ft of torque, the L5P Duramax is capable of towing just about anything you can throw at it.
The L5P turbo runs a highly efficient Radial flow turbine that measures 70 by 62.7 mm. The radial flow style turbine is built with an integrated heat shield and designed to work with a variable geometry vane cage.What year L5P is best? ›
The safest Duramax model years you can buy are the models produced from 2011 to 2021. These include the Duramax LGH, Duramax LML, Duramax XLD25, Duramax XLD28, Duramax LWN, Duramax L5P, and Duramax LM2. These engines go a step further to provide better emissions thanks to a diesel exhaust fluid/urea injection feature.What is the best fuel mileage for L5P? ›
Note the best "before" MPG recording was 24 MPG. In Level 1 (economy mode), we saw a best of 33.6 MPG at 65 MPH, and at 75 MPH, we saw 24.7 MPG average (between 23 and 26 MPG) on our 1,200 test trip. Overall, this is guaranteed smile-maker addition to your truck.How long should I let my L5P warm up? ›
If the temperature is between zero and fifty degrees, the warm-up period should be three to five minutes. Over fifty degrees will only require one or two minutes to warm up. This warm up time is necessary to increase the temperature of the combustion chamber.Is it worth deleting L5P? ›
Deleting the L5P DPF system is common for both preventative maintenance and performance reasons. Not having all these complicated systems reduces potentially expensive repairs, and also allows for more power production.
6.6L V-8 L5P Features
This next-generation redesign offers more horsepower and torque than ever — an SAE-certified 445 horsepower (332 kW) and net 910 lb. -ft.
It's the electronic side of the transmission sensing excessive slipping and placing the unit in fail-safe mode, where only one forward gear is available. As you've probably deduced up to this point, the stock Allison will handle roughly 350 to 400-rwhp in five-speed form and 425 to 450-rwhp in six-speed trim.What is the fastest stock Duramax? ›
Brett Deutsch's 1969 Chevy C10 currently holds the record for the fastest diesel-powered Pro Stock truck in the quarter mile. Under the hood is this single-turbo LLY Duramax engine.What Duramax can make the most power? ›
L5P. The L5P Duramax is the latest version of the Duramax V8 diesel engine. (engine code Y) Introduced in the 2017 model year it is the most powerful diesel engine GM has produced with 445 hp (332 kW) at 2,800 rpm and 910 lb⋅ft (1,234 N⋅m) at 1,600 rpm.What is needed to delete an L5P? ›
- You will require an HP Device, Canbus Plugs, and an Unlocked ECM.
- With the HP Device perform an Info Log before removing the ECM for unlocking.
- Remove the ECM and send it in. ...
- Once you receive the unlocked L5P ECM read the tune using the HP Device.
They still call this engine the L5P generation. It's now rated at 470 horsepower and 975 lb-ft of torque.What is the lifespan of a L5P? ›
With proper maintenance, the L5P should be able to easily clear the 350,000 mile mark, with some owners claiming they have had virtually zero issues through the 400,000 and 500,000 mile mark. Overall, these engines have proved to be extremely reliable.Is the L5P downpipe worth it? ›
The biggest benefit of an upgraded downpipe on the L5P is the reduction of backpressure. Less backpressure means more power and torque. Additionally, it lowers EGTs, creates a quicker turbo spool, and reduces stress placed on the turbo itself. On a completely stock L5P you probably won't notice a ton of power gains.What is the biggest stock Duramax turbo? ›
11.2mm on the LML engine available from '11-'16). This translates into the LLY possessing the highest flowing factory turbocharger.
All modern diesels are beasts, but the L5P Duramax in GM's '17-present heavy-duty trucks is exceptional. From the factory, the latest 6.6L diesel V8 produces 445hp and 910 lb-ft of torque at the crank.
The GM L5P Duramax is a turbo-diesel engine produced by General Motors for use in full-size heavy-duty (HD) pickup trucks. Displacing 6.6 liters in a V-8 configuration, the L5P is part of a new generation of Duramax engines. It succeeds the 6.6L Duramax V-8 LML engine.What comes after the L5P? ›
|Engine RPO Code||Production (model years)||Engine Block Material|
|LWN||2014 - Present||Cast grey iron|
|L5P||2017 - Present||Cast iron|
|LM2||2019 - Present||Cast aluminum|
|LZ0||2023 - Present||Cast aluminum|
LinCo Diesel Performance does it all, whether that be transmission work, maintenance and repair, or performance builds. Their prowess in Duramax and Cummins applications make them one of America's Best Engine Shops!What pump does the L5P have? ›
On the L5P, a Denso HP4 injection pump replaces the Bosch CP4. 2 found on the LML. The pump is still located at the front of the lifter valley, but the HP4 uses three high-pressure cylinders vs.How do you get 30 MPG on a Duramax? ›
You can get 30 mpg with a Duramax engine through several ways, including replacing older vehicle parts, adjusting the cooling and exhaust system, using good quality fuel, or getting a new engine system entirely. Changing the powertrain, radiator, or drive shaft might help you get the desired results.How many gallons of oil does a L5P Duramax take? ›
The maximum oil consumption for the 6.6L Duramax™ Diesel engine (RPO L5P) is 2.36 liters (2.5 qt) within 379 liters (100 gallons) of fuel used.What year Duramax gets best fuel mileage? ›
As far as I can tell the best years for mileage are 2001-2004 or so. Seems like they got into a horsepower war with Dodge and Ford after that and MPGs suffered.How much HP can a stock Allison transmission handle? ›
As you've probably deduced up to this point, the stock Allison will handle roughly 350 to 400-rwhp in five-speed form and 425 to 450-rwhp in six-speed trim. However, if you push things past that point the clutches will eventually slip and bring on the Allison's notorious “limp mode” condition (i.e. limp home mode).How much power can a stock 6.6 Duramax handle? ›
Factory 6.6L Duramax engines will make 300 to 397 flywheel horsepower depending on the model. Virtually any model can be bumped up to around 600 hp (about 480 rwhp) with simple computer tuning, provided that the turbocharger and fuel system are in good working order.How much horsepower can you get out of a 6.6 Duramax? ›
This next-generation redesign offers more horsepower and torque than ever — an SAE-certified 445 horsepower (332 kW) and net 910 lb. -ft. (1,234 Nm) — to enable easier, more confident hauling and trailering.