The 5 Best Duramax LMM Performance Upgrades

A few simple performance upgrades can take the Duramax LMM to over 500whp. We’re going to cover the five best mods to get it there: tuning, a cold air intake, exhaust, downpipe, and intercooler.

These upgrades alone can easily add over 100whp and 200wtq, pushing the LMM up against some of its performance roadblocks. So we’ll also cover power limits of the various engine systems and supporting mods for reliability.

Getting the LMM to 600whp and past is really expensive ($15k+) so we’re going to save these upgrades for a separate article.

Engine Power Limits

It’s pretty easy to achieve big power gains from performance upgrades on the LMM, but there are a few hurdles to discuss. Piston and crankshaft failure are common LMM problems. While they aren’t necessarily weak, they are a performance restriction. The OEM piston and crank can handle about 600-650whp before they are likely to crack. Therefore, pushing past 600whp will require a built motor unless you want to risk blowing yours.

However, your Allison 1000 transmission will limit performance before the pistons do. The Allison can handle about 450-500whp before it needs to be built. But, to run 450whp+ on it you will need a TCM tune to keep it reliable. Keep this in mind as the mods on this list will easily push you into 450whp territory.

The stock turbo can handle around 550whp until it needs to be upgraded. A lift pump is recommended once you are around the 500whp mark. Fortunately, with a lift pump you won’t need injector upgrades until somewhere around the 600whp mark.

Best Duramax LMM Performance Mods

• ECM & TCM Tuning
• Cold air intake
• Downpipe
• 4″ or 5″ exhaust
• Intercooler

If you would rather consume this content via a video, check out our How to Build a 450 WHP Duramax LMM video below:

1) Engine & Transmission Tuning

The best bang-for-the-buck LMM Durmax upgrade is a tuner. A simple tuner can add up to 100whp for just a few hundred bucks.

EFI Live is probably the most powerful tuning software for Duramax engines. You can also buy pre-built tuning packages for EFI Live so that it works more similarly to a handheld pre-loaded tuner. One of the best benefits of this software is that it also offers transmission tuning which is recommended since tuning can almost get you to 450whp alone.

If you just want some solid and easy power gains, you can stick to something like SCT, Edge, Bully Dog, etc. These are great options that are more cost effective, but if you are looking for more robust tuning capabilities then we recommend EFI Live.

Performance Benefits

• 30-100+whp and torque gains
• Better gas mileage
• More reliable transmission with TCM tuning
• Maximizes gains from other mods
• Easy install
• Best price per hp of any mod

2) Cold Air Intake Upgrade

An upgraded intake is our second favorite LMM Duramax upgrades since it is one of the best mods to combine with a tuner. With tuning it’s important to supply the turbo with more air and greater air density since it needs to compress a greater volume of air.

In addition to improving turbo efficiency and providing power gains an intake will also provide gas mileage improvements, better throttle response, and faster turbo spool in addition to power gains.

We prefer open intakes to closed intakes. Open intakes have bigger airflow increases over closed intakes. The extra flow will help provide bigger power gains, and reduce restriction on the turbo.

Power Gains

• Approx. 20whp and 40wtq gains when tuned
• Faster turbo spool
• Better throttle response
• 1-2mpg improvements
• More efficient and therefore healthier turbo
• Cool intake noises

The power gains we quoted aren’t necessarily peak power gains, but rather max power gains throughout various parts of the power curve.

Make sure to check out our Duramax LMM Cold Air Intake Guide for the top recommendations.

3) Downpipe Upgrade

Within the exhaust system a downpipe will provide the best power gains and backpressure reduction since the downpipe bolts directly to the turbo.

The stock downpipe is crushed and very restrictive, creating a lot of backpressure. Since it’s bolted to the downpipe this backpressure actually works against the turbo, making it harder for the turbo to spin its compressor wheel. This puts stress on the turbo, restricts performance, and also increases EGTs and engine temps.

Upgrading the LMM downpipe will improve the efficiency of the turbo, unlock solid power gains, and decrease engine temps and EGTs. Ultimately, it is one of the best reliability mods and also offers great performance gains.

Downpipe Performance Benefits

• Approx. 15whp and 25wtq power gains
• Less backpressure in exhaust
• Lower EGTs
• Better turbo efficiency and reliability
• Healthier engine

4) 4″ or 5″ Exhaust System

Deleting the DPF filter is probably the best exhaust mod. But a larger 4″ or 5″ DPF-back exhaust system will still help reduce exhaust backpressure. Therefore, it will benefit the turbo and help reduce EGTs a bit more. The larger you go the more flow increase you will see and therefore the more benefit to power gains and EGTs.

You have a few options with exhaust systems. First is sizing, 4″ or 5″ systems are the most popular. You can also choose to get an exhaust with a muffler or go full straight-pipe. Material wise you can get an aluminum exhaust or stainless steel. Pricing on exhausts range from $400-$1,000 depending on the materials you want and sizing.

Upgrade Benefits

• 5-8whp and 10-15wtq gains
• Decreased exhaust backpressure
• Lower EGTs
• Louder exhaust note

5) Upgraded Intercooler

While intercooler upgrades are expensive they are one of the best reliability upgrades for tuned and modified LMM’s. You won’t necessarily see a ton of power gains from an intercooler but you will see cooler engine temps and lower EGTs, especially if you tow frequently.

At 500whp, you probably don’t need an upgraded intercooler as the stock intercooler is pretty solid. However, it doesn’t hurt. It will still lower EGTs, improve reliability when tuned, and provide more consistent performance. It’s a great mod for anyone who pushes their truck hard or tows a lot.

Benefits

• Lower EGTs
• 30%-50% improvement in air capacity and flow
• Consistent performance
• Improved reliability when tuned
• Marginal gas mileage improvements

Summary

The LMM makes pretty good power from the factory with 365hp and 660lb-ft. of torque. However, for those who want more power 5 simple bolt-on mods can easily add over 100whp for just a few thousand bucks. These simple mods should be able to get you to or past the 450whp mark which is where these engines gets a bit more expensive to mod.

The Allison 1000 transmission needs to be tuned to hold 450-500whp consistently. Anything about 500whp and you’ll need a built transmission. The stock turbo is good for about 550whp until you’ll need to upgrade that. Fuel injectors are good until about 600whp, but a lift pump is recommended once you pass the 450whp mark or so. Lastly, the pistons and crank are good for about 650whp until they need to be upgraded.

Overall, getting to big power numbers can be quite expensive. However, adding an extra 100whp can be done pretty easily without sacrificing too much reliability. Our favorite bolt-on mods are a tuner, intake, downpipe, exhaust, and intercooler. A DPF delete is a great mod for the LMM if you are comfortable having a deleted truck.