Duramax LMM downpipe

Duramax LMM Downpipe Upgrade Guide

Jake Mayock

Meet Chandler

Chandler is a leading content writer for 8020 Media. Outside of writing truck related GM content for Chevy Trucks he creates a lot of articles around LS engines over on TuningPro. Chandler is a gearhead with tons of hands-on experience. Furthermore, he has a masters degree in history that makes him invaluable in crafting high-quality, well-researched articles on both classic and modern Chevy trucks.

One of the most restrictive components on the Duramax LMM is the factory downpipe. It is crushed and limits exhaust flow leading to increased backpressure. Ultimately, this leads to higher EGTs, decreased engine efficiency, and puts more stress on the turbocharger.

Upgrading the factory downpipe to a larger 3″ performance downpipe is one of the best performance mods for the LMM. In this guide we’re going to cover the benefits of a downpipe upgrade and highlight our own in-house product, manufactured by our Boosted Performance brand.

Duramax LMM Downpipe Upgrade
Credit: Boosted Performance

The Restrictive Factory Downpipe

The factory downpipe is crushed, and not a perfect round piece of piping. With a 3″ connector to the turbo, the crushed piping that is skinnier than 3″ creates a lot of backpressure within the exhaust.

Backpressure acts as a force against the turbo, decreasing its efficiency and resulting in slower spool. Ultimately, it restricts engine power and also causes the turbo to run hotter, resulting in higher EGTs which is bad for performance.

Downpipes vs. Deletes

Another common upgrade on the LMM when doing the downpipe is to delete the diesel particulate filter (DPF). The DPF is located directly after the catalytic converter and before the muffler.

The downpipe is a completely separate pipe from the DPF and it does not feature any emissions equipment within it, making a downpipe upgrade completely legal from an emissions standpoint.

Duramax LMM Downpipe Upgrade Benefits

  • +10-20whp and 20-30wtq
  • Decreased back pressure
  • Lower EGTs
  • Greater exhaust velocity
  • Increased engine and turbocharger efficiency
  • Healthier engine and turbo

The most noticeable benefit of upgrading the Duramax LMM downpipe is going to be the increase in power. With a freer-flowing downpipe, you can see gains of 10–20 horsepower and 20-30 lb-ft of torque. Most of these gains will be from the decreased back pressure of a larger downpipe, which increases exhaust flow velocity.

The second biggest benefit is the reduction in EGTs. Less backpressure means less stress on the turbo which in turn means less heat being produced by the turbo. This will cause EGTs to lower which is going to improve both the reliability of the turbo and the engine overall.

Boosted Performance LMM 3″ Downpipe

Duramax LMM Downpipe Upgrade

Price: $219
Material: 304 Stainless Steel
Buy Here: Boosted Performance LMM 3″ Downpipe

Our favorite downpipe for the LMM comes from Boosted Performance, of course, it’s our own brand. It’s made of 304 stainless steel, it has a nice heat shield on it, fitment is great and it works on both factory and aftermarket exhaust systems, and it doesn’t require any tuning or additional modifications. Weld quality is great and it comes in at a good price point.

At 3″ this downpipe is a lot less restrictive than the factory unit and therefore will have a big impact on backpressure reduction and improved performance. At $219 it isn’t the cheapest option on the market but it is one of the best values when you consider materials, quality, and fitment.

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