Duramax LML Downpipe Upgrade Guide

One of the best performance upgrades for the Duramax LML is a 3″ downpipe. A downpipe will help reduce exhaust backpressure, providing good power gains in addition to lower EGTs, faster turbo spool, better gas mileage, and more.

Through our performance brand, Boosted Performance, we’ve been making downpipes and performance products for Duramax engines for years. In this guide we’re going to give you our inside knowledge on the performance benefits and reasons for upgrading the LML downpipe.

If you are interested in learning more about engine upgrades, check out our 5 Best Duramax LML Performance Mods Guide.

The Crushed Factory Downpipe

The primary goal of a downpipe 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”, 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 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 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. 

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.

Combining a Downpipe with an 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. 

Duramax LML Downpipe Upgrade Guide Summary

Upgrading your LML Duramax’s downpipe offers some significant and varied benefits. 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. 

Overall, upgrading your LML Duramax downpipe is a worthwhile investment for better engine performance and longevity.

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