Duramax LML Downpipe Upgrade Guide

By the time the 2010s rolled around, the Duramax engine was on its 6th iteration, the LML. As an extension of the LMM engine that introduced heavy emissions regulation technology to the engine, there are quite a few ways to improve on the 2011-2016 LML. That is actually a good thing, as the LML is an engine that has ample power potential and a large aftermarket community. One of the best ways to actualize some more potential from the 6.6L turbo diesel V8 is by installing an upgraded LML Duramax downpipe.

LML downpipes offer excellent value for money and provide numerous advantages for your engine. By upgrading your Duramax downpipe, you can experience significant improvements in various areas. These include reducing exhaust gas temperatures (EGTs), enhancing turbo response, improving fuel economy, and unleashing additional horsepower that may be trapped by the crushed factory design.

This comprehensive guide will delve into the details of Duramax LML downpipe upgrades, exploring their benefits and highlighting the top options currently available on the market. If you are interested in learning more about Duramax LML engine upgrades, also check out our 5 Best Duramax LML Performance Mods Guide.

What is a Duramax LML Downpipe?

Before we jump into the specific details surrounding how an upgraded LML downpipe can help your Chevy/GMC, let’s talk about what a Duramax downpipe actually is. To clear up any confusion out of the gate, Duramax downpipes are sometimes called turbo direct pipes in the Duramax community. Regardless of what they’re called, they serve the same purpose. 

The primary goal of a Duramax downpipe, and downpipes in general, is to get exhaust gasses away from the turbocharger and send them on to the rest of the exhaust system. Being the initial exhaust component following the turbo, it is crucial to ensure that your downpipe is optimized for effectively channeling exhaust gases away from the turbo, minimizing airflow obstacles, and maintaining the lowest possible temperature. 

The factory LML downpipe is practically the opposite of that, as it is skinny and prohibitive to airflow. While the factory “crushed downpipe” as some Duramax enthusiasts call it, is generally just fine for stock trucks, it will become a limiting factor if you intend on upgrading other components down the line. However, an upgraded downpipe provides benefits for stock trucks, too. A well-engineered Duramax LML downpipe is specifically designed to minimize backpressure at the turbo outlet. That alleviates strain on the turbine and enhances its performance.

Duramax LML Downpipe Upgrade Benefits

• Decreased EGTs
• Increased turbo response
• Better sound at WOT and idle
• 5-10whp gain on stock turbo without tune
• 15-40whp gain with upgraded turbo and tune
• 1-5 MPG improvement

As with nearly any turbocharged engine, upgrading your LML downpipe has a number of important benefits. Some of those are surface-level benefits like improved sound, while others are directly related to performance.  Ultimately, an upgraded LML downpipe isn’t a power modification on its own. However, the effects that an upgraded downpipe has on turbo efficiency and engine health can be notable. 

Due to the fact that upgraded LML downpipes are designed to reduce turbo backpressure, they also have a positive effect on exhaust gas temperatures. Exhaust gas temperature, or EGTs, is one of the most important parameters to keep your eye on in a Duramax truck. That is especially true if you are towing or putting your truck under a heavy load. If your LML’s EGTs get too high, it can cause structural issues for your turbo and Duramax itself. 

Aftermarket LML Downpipes typically have better thermal properties than the stock unit, reducing EGTs by up to 100 degrees Fahrenheit, while also cooling faster after a period of intense heat. This not only keeps your LML healthier but also helps improve turbo efficiency and response.

Due to the fact that the factory LML downpipe hampers exhaust flow, you’ll see a bit of added performance with a better-optimized downpipe. However, it is important to note the performance gains that you see from an upgraded LML downpipe scale with other modifications. You might only pick up 5-10 horsepower from a stock-turbo, untuned LML V8. You’ll see far better improvements when paired with an upgraded exhaust and a tune. 

LML Duramax Downpipe Considerations

Due to the fact that the Duramax V8 engine series is so popular among enthusiasts, the aftermarket parts space is competitive. That is great news, as there are a number of quality downpipes to choose from numerous different parts manufacturers. While more options are always better than fewer options, choice paralysis can set in pretty quickly. 

The most important factors to consider before pulling the trigger on a Duramax downpipe are quality, build materials, and price. Outside of the downpipe itself, you should also think about other modifications that work well with an upgraded LML downpipe. Other exhaust and tuning-related modifications can compound the effect of a downpipe. 

LML Downpipe Material

Build materials are one of the most important factors in choosing the right LML Duramax downpipe for you. A Duramax downpipe is a simple piece of equipment that is designed in nearly an identical way between part manufacturers. Since the structure of the part is pretty consistent across the board, using high-quality materials is one way for a Duramax downpipe manufacturer to set themself apart. 

Steel is the most common material used to construct Duramax downpipes. It is important to pay attention to the kind of steel that is used to build the part. The type of steel plays a big role in corrosion and rust resistance and overall longevity. Most LML downpipes are made of either aluminized steel, 409 steel, or 304 steel, each with benefits and shortcomings. 

Out of the three, aluminized steel stands out as the most budget-friendly for both production and buying. It also has fantastic thermal conductivity, making it a good material for a downpipe. However, its durability diminishes significantly over time. That is especially true when exposed to road salts used for snow melting during the winter season. Extended contact with these substances causes aluminized steel to rust and corrode. 

409 stainless steel is the next step beyond aluminized steel in terms of price and corrosion resistance. While slightly more expensive, 409 downpipes will undoubtedly hold up better over an extended period of abuse. 

Lastly, we have 304 stainless steel. Of all of the most common materials used to build downpipes and other exhaust components, 304 stainless steel is by far the best in terms of durability. Its material makeup makes it nearly impervious to rust or corrosion. With that being said, it is the most expensive to produce and buy.

Getting the Most From an LML Downpipe

An LML downpipe is not a power modification on its own. While it provides undeniable benefits for EGTs and turbo health, a Duramax downpipe will only produce notable performance benefits when paired with other modifications. 

Since an upgraded Duramax downpipe decreases backpressure and helps push more exhaust gas away from the turbo, it only makes sense to upgrade the rest of your LML’s exhaust system as well. In the LML, a catalytic converter comes immediately after the downpipe. Depending on the emissions requirements in your state, a Duramax straight pipe exhaust or cat-back can help carry the benefits of a freer-flowing downpipe all of the way through the exhaust system, freeing up some power and noise. A Duramax straight pipe exhaust will provide the best performance, as there is no cat creating a restriction.

A tune is another way that you can heavily benefit from an upgraded Duramax downpipe. Due to the fact that Duramax tuners typically increase power by adjusting boost parameters, a downpipe can help the turbo operate even better. Whether you go with a plug-and-play tuner like an Edge CTS3 or a custom tuner like an EFI Live Autocal, the performance gains are massive. This Duramax tuner/downpipe pairing is compounded even further with a full LML exhaust. 

Duramax LML EGR Delete

While a Duramax EGR delete isn’t directly related to an upgraded LML downpipe, their effects compound very well together for even better EGRs and overall performance. Since we’ve already written a Duramax LML EGR delete guide, we’ll keep it brief here. In essence, an LML EGR delete gets rid of the engine’s exhaust gas recirculation system. This system recirculates a portion of the LML’s exhaust gasses back into the engine to be re-combusted. Its purpose is to remove some of the diesel particulates and improve emissions. 

However, recirculating dirty exhaust gasses back into the engine is bad for both performance and reliability. Not only does it increase EGTs and combustion temperatures, it leads to internal soot buildup that can cause problems later on. By removing this system altogether, you’ll see marginally improved performance in the short term and increased reliability in the long term. 

So, what does this have to do with a Duramax LML downpipe? Well, when paired together, an EGR delete and an upgraded downpipe can make a serious impact on reducing EGTs. As we mentioned earlier, that is important if you are running into overheating issues when towing. Both components also increase performance on their own, with even greater power gains when paired together and with a tune. 

Best LML Duramax Downpipes

The LML, and the entire Duramax family for that matter, is extremely popular. For that reason, there are quite a few decent upgraded LML downpipes on the market currently. It also helps that the LML was released over 10 years ago. That has given big names in the diesel exhaust space plenty of development time. Here are our recommendations for the best LML Duramax downpipes available currently:

• Boosted Performance Duramax LML Downpipe
• PPE 3”
• MBRP 3”
• ProFab 3” LML Downpipe

Since LML downpipes lack catalytic converters across all products, the differentiating factors among the leading options are pretty minor. As a result, most of the leading LML downpipes on the market are almost identical in terms of shape. However, factors such as construction materials, thermal properties, and flow characteristics remain significant considerations for LML downpipes. 

2) MBRP 3” 6.6 Duramax V8 Performance Downpipe

Price: $254.99

Purchase Here: mbrpexhauststore.com

MBRP’s LML downpipe is unquestionably one of the most popular and well-known downpipes in the Duramax scene. With years of experience under their belt, the MBRP team has established a strong presence in the industry. Since its inception in 1996, MBRP has gained recognition for their commitment to customer satisfaction and the production of top-notch products. As a family-owned business rooted in Canada, MBRP’s operations have consistently prioritized quality, a principle that has endured over time.

MBRP has engineered their LML Duramax 3″ downpipe to maximize efficiency to the furthest extent possible. Employing a mandrel bending process, they have achieved a remarkably smooth internal surface, that guarantees optimal flow. Additionally, the MBRP Duramax downpipe is fully heat wrapped to improve Exhaust Gas Temperatures (EGTs). As a member of their BLK series, this MBRP downpipe is expertly crafted using 16 gauge aluminized steel and finished with a sleek black ceramic coating.

While the MBRP LML downpipe is unquestionably one of the best on the market, it does fall short in a couple of key areas. For one, it is made from aluminized steel and therefore more prone to corrosion. There are also claims in the community that the MBRP Duramax downpipe is a tight squeeze in the engine bay.

3) PPE Duramax V8 3” Downpipe

Price: $189.91

Purchase Here: ppepower.com

Pacific Performance Engineering is a name that often goes under the radar in the Duramax community. While they have been around since 1985, their Duramax downpipes are often overlooked in favor of MBRP. To be honest, it’s hard to tell why. PPE is known for their advancements to the Duramax tuning space, with contributions like the PPE Duramaximizer. While they are known for their pioneering efforts in making Duramax’s faster, they have some very good exhaust components too. 

The PPE LML downpipe is the only other downpipe, besides Boosted Performance’s, on this list that is made from the highest-quality 304 stainless steel. That makes it a lifelong product that you won’t have to replace in the future due to damage or corrosion. Like the other entrants on this list, PPE uses mandrel bending to shape their pipes. For enhanced thermal efficiency, the PPE LML downpipe is wrapped in a woven titanium sleeve, reducing engine bay temps. 

In addition to the PPE downpipe’s superior build quality, it is also 50 States Emissions Legal. That means that it can be purchased and shipped to California, unlike many other Duramax downpipe options. It is also equipped with three sensor bungs, meaning that all of the factory Duramax downpipe sensors can be retained. 

While there are certainly more pros than cons with the PPE downpipe, fitment is one main gripe among enthusiasts. Most Duramax owners that have purchased the pipe claim that it is about ⅛” too long, causing a slight exhaust leak at the turbo. 

4) ProFab 3” Duramax LML Downpipe

Price: $213.55

Purchase Here: profabperformance.com

Completing our lineup is a noteworthy LML Duramax downpipe produced by a well-known American manufacturer. ProFab is a company dedicated to delivering both value and performance. ProFab Performance Parts, originally established as a repair shop near Kansas City, has expanded its scope to encompass the manufacturing aspect of the automotive industry, with a specific focus on Duramax performance parts.

Their commitment to quality is evident in their meticulous manufacturing process, utilizing in-house mandrel bending and CNC equipment. Crafted from aluminized steel and coated with a ceramic finish, the ProFab 3″ LML downpipe is further enhanced by a heat wrap. This comprehensive approach ensures exceptional heat management, making it one of the top choices for effectively reducing Exhaust Gas Temperatures (EGTs).

While the ProFab 3″ Duramax downpipe has garnered praise from numerous Duramax and LML enthusiasts for its impressive performance, it is worth noting that some users have mentioned installation challenges due to its design and heat shielding.

Duramax LML Downpipe Upgrade Guide Summary

Upgrading your LML Duramax’s downpipe offers some significant and varied benefits for your 6.6L turbo diesel V8. It helps reduce exhaust gas temperatures, improves turbo response, enhances fuel economy, and unlocks additional horsepower that may be restricted by the factory design. 

The aftermarket community for LML engines is robust, providing a wide range of options to choose from. When selecting a downpipe, factors such as build materials, quality, and price should be considered. Materials like aluminized steel, 409 stainless steel, and 304 stainless steel offer varying degrees of durability and corrosion resistance. 

It is important to note that while a downpipe alone won’t provide substantial power gains, combining it with other modifications such as an upgraded exhaust system and a tune can maximize performance benefits. Additionally, pairing a downpipe with an EGR delete can further improve exhaust gas temperatures and overall performance. 

Among the recommended options for LML Duramax downpipes are Boosted Performance, MBRP, PPE, and ProFab, each offering their own advantages in terms of construction materials, thermal properties, and flow characteristics. Overall, upgrading your LML Duramax downpipe is a worthwhile investment for better engine performance and longevity.