Duramax LBZ Downpipe Upgrade Guide

An upgraded downpipe is one of the best performance upgrades for the Duramax LBZ. It provides power gains, lowers EGTs, improves turbo spool, and improves engine efficiency. Overall, it is one of the best performance and reliability upgrades available to these engines.

With experience manufacturing performance downpipes for the LBZ, we’re going to give you the inside scoop on the performance benefits and issues with the factory downpipe.

The Crushed Factory Downpipe

Duramax LBZ Downpipe Upgrade

The downpipe is the first component of the exhaust system which attaches to the turbo exhaust housing to the rest of the exhaust system. Due to their proximity to the turbocharger, 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. 

Duramax LBZ 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

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 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 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. 

LBZ’s with an upgraded downpipe will get 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 exhaust is the way to go in addition to a downpipe.

Maximizing Exhaust Upgrades

Although a 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 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.


The Duramax LBZ, 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 a 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.

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