Duramax LBZ Downpipe Upgrade Guide

As the third entry into the Duramax family, GM had learned a few things about how to build a turbo diesel V8. Introduced halfway into the 2006 model year as a replacement for the outgoing LLY Duramax, the LBZ improved on a few notable design defects with the previous model. Additionally, the LBZ existed in a sweet spot before emissions regulation technology got extreme, making it a favorite in the community due to its simplicity. 

When it was initially launched, the LBZ produced 360 horsepower and 650 lb-ft of torque. While that was a significant leap over the outgoing LLY’s 310 horsepower and 605 lb-ft, those numbers pale in comparison to the true power potential resting inside the LBZ. With a few choice modifications, quite a bit of untapped performance can be unleashed from the 6.6 Duramax. An upgraded LBZ downpipe is one of those modifications. 

Upgraded LBZ downpipes not only improve the efficiency of your exhaust but also lower exhaust gas temperatures, improve turbo response, protect turbo health, improve sound, and untangle some power. In this article, we’ll cover the benefits of upgrading your Duramax LBZ downpipe, aspects to consider when buying one, and a few of the LBZ downpipes that we recommend. 

Credit: MBRP Exhaust Store

What is a Duramax LBZ Downpipe?

On the LBZ Duramax, the downpipe is the first component of the exhaust system which attaches to the turbo exhaust housing to the rest of the exhaust system. Downpipes are also sometimes referred to as “turbo direct pipes” in the Duramax community. Due to their proximity to the turbocharger, LBZ Duramax downpipes play the most vital role in the exhaust system. 

As a general principle, the more efficiently you can get exhaust gas away from the engine, the better performance you’ll see. That is especially true for turbocharged/turbo diesel engines, as turbos rely on an effective exhaust system to work as well as possible while suffering as little damage as possible. Excessive backpressure is the enemy of both performance and turbocharger health, as exhaust gas that is trapped in the exhaust system can cause the turbocharger to work harder than needed, putting additional strain on the turbine.

The design of the factory downpipe on all Duramax engines is extremely restrictive. One of the main problems with the factory downpipe is its shape. Unlike aftermarket LBZ downpipes that are designed with smooth airflow in mind, the stock unit is crushed, creating poor airflow characteristics. 

Upgraded Duramax LBZ Downpipe Benefits

Upgrading your LBZ Duramax’s downpipe has some notable benefits that pertain to both performance and engine health. While there are conflicting reports on this front, an upgraded Duramax downpipe isn’t a significant power upgrade by itself. You’ll generally have to add other exhaust and intake modifications to reap the true power benefits of an upgraded downpipe. With that being said, the benefits to EGTs, turbo health, turbo response, and sound make it a worthy upgrade.

  • 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

Decreased EGTs

For LBZ owners that put their Chevy/GMC truck to good use, like towing heavy loads, lower EGTs are likely the most obvious reason for upgrading your LBZ downpipe. EGTs, or exhaust gas temperatures, are extremely important to monitor, as excessively high EGTs can cause damage to your turbo and engine itself. Upgraded LBZ downpipes generally have better thermal properties than the stock unit, lowering EGTs while also cooling off faster than a stock downpipe. 

Turbo Performance and Health

In addition to EGT improvements, upgraded LBZ downpipes provide some noticeable benefits for turbo performance and health. This boils down to reducing backpressure, as the less a turbocharger has to fight to expel exhaust gas, the easier it is for it to spool and perform efficiently. By reducing how hard the turbo has to work, its overall longevity is also improved. 

Better Sound

Another, somewhat underrated, benefit of an upgraded downpipe is its effect on the sound of a Duramax. While this is obviously a matter of personal preference, some people enjoy the deeper rumble at higher RPMs associated with an upgraded downpipe. This is especially true for LBZ owners that have a straight pipe exhaust that drones around the 2,500-4,000 RPM range. 

Most LBZ owners with an upgraded downpipe say that it gets rid of the high-pitched WOT screeching sound and replaces it with more pronounced turbo sounds instead. However, if you are seeking out better exhaust sounds primarily, an upgraded LBZ exhaust is the way to go. You have a couple of options on this front.

Duramax LBZ Downpipe Upgrade Considerations

With so many Duramax downpipe options on the market, it can be hard to decide which one is the best option for you. Luckily, LBZ downpipes are a relatively simple component. It is a small pipe connecting the turbo to the catalytic converter. As a result, there isn’t much variation in terms of the part itself. With that being said, quality, materials, fitment, and price are all important to consider before pulling the trigger.

The overall quality of an LBZ downpipe is perhaps the most crucial aspect to consider when buying one. This boils down to the fit and finish of the part. Was the downpipe formed with mandrel bending tech? Is it painted to prevent rust and corrosion? Does the downpipe feel solid in your hand? Some of these questions are easier to answer than others. However, the Duramax community has gone pretty in-depth with most parts out there

Materials are another very important factor to consider. Most Duramax downpipes are either made from aluminized steel or stainless steel. While aluminized steel has some benefits as a downpipe material, like superior thermal conductivity, it is very prone to rust and corrosion, especially in places where roads are salted in the winter. 409 and 304 stainless steel are more expensive to manufacture and purchase but they hold up much better to corrosion over time. 

Fitment is another very important aspect to consider as the LBZ leaves little physical room for a downpipe. In some cases, heat dispersion techniques used by some manufacturers, like a bulky thermal wrap, can cause problems with fitment.

Getting the Most From an LBZ Downpipe

Although a Duramax downpipe certainly offers significant advantages in terms of EGTs and turbo health, you’ll really only see notable performance benefits when it is combined with other modifications. Other exhaust modifications, intake modifications, and tuning are the best ways to increase the benefits of an upgraded LBZ downpipe.


Upgrading your downpipe has a massive positive effect on reducing backpressure, but a quality LBZ cat-back exhaust can ensure that those benefits carry through the rest of the exhaust system. In most states, a catalytic converter is required to meet emissions requirements. As a result, most LBZ exhausts on the market are cat-back systems. Not only will a cat-back exhaust free up some additional power, but it will also improve your LBZ’s sound by a significant amount.

Tunes are truly one of the best modifications for any Duramax engine. That is because a factory Duramax can withstand a lot more power than it delivers in factory form. Most handheld tuners and custom tunes increase horsepower by adjusting boost parameters. 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. Since an upgraded downpipe improves turbo efficiency and reduces backpressure, the benefits of a tune are more pronounced when combined with a downpipe.

Best LBZ Duramax Downpipes

Since the Duramax LBZ has been around for so long, there are quite a few downpipe options to choose from. Almost every Duramax parts manufacturer has something on offer for the LBZ. However, there is a fair bit of variety in terms of what each manufacturer brings to the table. While the actual downpipe doesn’t vary very much in terms of shape, build materials, quality, and price are all important considerations. 

  • Boosted Performance Duramax LBZ Downpipe
  • PPE 3” LBZ Downpipe
  • Diamond Eye 3” LBZ Downpipe

2) Diamond Eye LBZ Performance Intake

Price: $203.29

Purchase Here: Dieselpowerproducts.com

Diamond Eye is a name that has been around for a long time in the Duramax community. Almost every Duramax downpipe thread on the internet makes mention of Diamond Eye which should speak to their influence. They got their solid reputation a reason, too. Based out of eastern Oregon, Diamond Eye manufactures all of their components in-house. With their own CNC and mandrel bending machines, Diamond Eye is committed to advancing with the times.

The Diamond Eye LBZ intake is another 3” intake which is the perfect diameter for optimal airflow and velocity. While the Diamond Eye LBZ downpipe is aluminized steel, which isn’t the best in terms of rust and corrosion resistance, it is wrapped in a thermal-resistant band to help shield it from damage while also benefiting themal properties. Diamond Eye claims that their LBZ downpipe will help reduce EGTs by up to 150 degrees in the right circumstances.

One of the biggest upsides to the Diamond Eye LBZ downpipe is its fitment. The Duramax’s downpipe location makes it a pain to uninstall and reinstall. For that reason, it is important that a downpipe is the right width and length for the space. It is almost unanimously concluded that the Diamond Eye downpipe is the best-fitting option on the market.

3) MBRP Performance Duramax Downpipe

Price: $189.99

Purchase Here: MBRPexhauststore.com

Like Diamond Eye, MBRP is another name that gets a lot of love in the forums. Whether it’s because MBRP has been in the Duramax/Chevy performance game for over 20 years or because of their commitment to customer satisfaction and the production of top-notch products, MBRP has their praises sung nonstop. Their Canada-based operation has been going strong since 1996 and will likely endure well into the future.

MBRP has taken meticulous engineering measures to ensure the LML Duramax 3″ downpipe attains the best efficiency possible. Through the implementation of a mandrel bending process, they have achieved a very smooth internal surface, guaranteeing optimal flow. Furthermore, the MBRP Duramax downpipe is comprehensively heat wrapped, resulting in enhanced exhaust gas temperatures. As part of their esteemed BLK series, this MBRP downpipe is expertly crafted from 16 gauge aluminized steel and boasts a sleek black ceramic coating, showcasing both durability and aesthetic appeal. That will also help the aluminized steel resist rust and corrosion. 

While there are plenty of upsides, one of the main complaints with the MBRP downpipe is poor fitment. Most people agree that the MBRP downpipe is a bit too wide, causing it to barely fit in the bay. Some MBRP customers have had to hammer down 

LBZ Duramax Downpipe Upgrade Summary

The LBZ Duramax, known for its simplicity and power potential, can significantly benefit from a well-designed downpipe. Upgraded LBZ downpipes improve exhaust efficiency, lower exhaust gas temperatures (EGTs), enhance turbo response, and produce an improved sound. While the power gains from a standalone downpipe upgrade may not be significant, combining it with other modifications such as exhaust upgrades, intake modifications, and tuning can maximize its performance benefits.

Reducing EGTs is crucial for LBZ owners who tow heavy loads, as high temperatures can damage the turbo and engine. Upgraded downpipes provide better thermal properties, effectively lowering EGTs and allowing for a more efficient engine overall. Additionally, reducing backpressure enhances turbo performance and longevity by allowing easier spooling and efficient operation. That can be further amplified with an LBZ Duramax tune.

When selecting an LBZ downpipe, you should consider factors such as quality, materials, and fitment. While most downpipes are similar, they are not all created equal. A stainless steel downpipe will hold up much better over time than an aluminized one. Fitment is also important to consider since the space that you are working with is very tight. Several manufacturers offer LBZ downpipes, each with its own unique features and price points. Boosted Performance, Diamond Eye, and MBRP are among the notable options, with each offering specific advantages in terms of construction quality, fitment, and thermal properties.

Why are you considering upgrading your LBZ Duramax downpipe? If you already have one, let us know your experience below. 

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