The 6.6L Duramax LML was released in 2011 and produced through 2016. Producing 397hp and 765lb-ft. of torque, the LML delivered solid power and was a strong competitor to Ford and Cummins 6.7L diesel engines of the time.
While the LML’s power is just about as much as anyone would need, there are still some significant performance and efficiency benefits that come from an upgrading the LML’s intake system. A cold air intake with not only increase horsepower through more airflow, but also reduce stress on the turbo, provide better throttle response, and provide small MPG increases.
An LML cold air intake is one of the best performance mods you can make, especially if you have a tune or plan on adding one. This guide will walk through the performance benefits of cold air intakes, discuss air intake temps, and provide some recommendations on our favorite LML intake upgrades.
Duramax LML Cold Air Intake Benefits
The term “cold air intake” is really just a marketing term when it comes to diesels. Intake performance benefits come from the increased airflow drawn in from the intake system rather than from the temperature of the air the intake is pulling in. Performance intakes for the Duramax LML will provide 30%+ increases over the stock intake system. The added airflow decreases stress put on the turbocharger, allows it to spool more quickly, and increases its efficiency which ultimately increases power.
Putting an upgraded intake on a stock LML won’t quite provide the same benefits on a tuned LML. Horsepower gains from an intake are greater when the LML is tuned. Tunes predominantly increase power by increasing boost pressure, or psi. When boost is added the stock intake system becomes restrictive as it does not flow enough air to the turbo.
Creating more power requires more combustion. More combustion requires more fuel and air. When boost increases, the air is compressed more. The more compressed air is the less space it takes up. Therefore, more air has to be sent into the engine. The stock intake becomes restrictive because it cannot flow enough air which puts extra stress on the turbo.
Here are the performance benefits of adding a cold air intake to the LML:
- Up to 20whp and 60wtq gains
- 30%+ airflow increase
- Faster turbo spool
- Increased throttle response
- 1-2mpg increases
- Sweet engine sound
LML Intake Horsepower Gains
The numbers of 20whp and 60wtq quoted above won’t necessarily be true on a stock engine. As mentioned, tuned engines will receive more power gains from an intake as the increased airflow is more beneficial when turbo boost is increased.
Additionally, these numbers as well as the numbers quoted from most companies don’t represent peak power gains. While these gains are accurate at low RPMs, the peak power gains will be a good bit lower. Peak power gains will more likely be in the 5-10whp and 10-20wtq ranges.
Cold air intakes are beneficial for low-end power and torque rather than high-end peak power. This makes an intake a great addition for anyone who does a lot of towing or who is looking for better acceleration.
LML Intake Upgrade: Best Intake Styles
As we mentioned above, the term “cold air intake” isn’t necessarily accurate. Most Duramax LML intakes are actually ram air systems. Cold air intakes generally re-route the location of the air filter so that it draws in colder air. Ram air systems keep the stock location of the air filter and focus on improved airflow.
All of the intakes available for the LML are ram air intake systems. They use the stock airbox location and focus on removing restriction to improve airflow. Point here is that you will see intakes called cold air intakes, ram air intakes, performance intake systems, and so on. Ultimately, they are all the same.
So ignore the name of the intake and instead focus on the style and design: open intakes vs. closed intakes.
LML Open Intake vs. Closed
The most important intake consideration is whether you choose an open or a closed intake. As the name suggests, open intakes have the air filter open and directly exposed to the engine bay air. Closed intakes keep the air filter enclosed within an airbox, therefore protecting it from the engine bay temps. A lot of open intakes will have “heat shields” that are supposed to protect the filter from the hot engine air. These are pretty much marketing ploys and not really very effective.
Pro’s of Open Intakes
- Provide more airflow than closed intakes since the box on closed systems is restrictive
- Greater power gains due to more airflow
- They are usually a bit cheaper since it’s less material
- Provide more intake “whoosh” sounds (could be a con)
Con’s of Open Intakes
- They draw in slightly hotter intake air temps (IATs) since they are exposed to the engine bay
- See our explanation below on why this really doesn’t matter
We always recommend open intake systems. They provide better power gains, are usually a bit less expensive, and give the greatest airflow increases. The only time we would recommend a closed system is if you wanted less intake noise. But overall, any upgraded intake is an improvement over the stock system. Unless you are planning on going full bolt-on and upgrading your turbo then a closed system will be just fine.
Intake Air Temps (IATs) and Why They Don’t Matter
If you’ve looked at upgraded intake systems before, you’ve probably seen the ‘hot air debate’. A lot of people claim upgraded intakes result in higher intake air temps. And, in a way they do. But it doesn’t really matter.
On a naturally aspirated engine, intake air temps do matter. The air goes through the intake and directly into the engine. Therefore, if you draw in air that is 5 degrees hotter it will be 5 degrees hotter when it goes into the engine. However, this isn’t the case for turbo diesel engines, or any turbo engine.
Intake air on turbo engines goes from the intake system to the turbocharger. Turbo’s are extremely hot, so they naturally increase the temperature of air. This is why turbo cars have intercoolers. Once the air is heated up and compressed by the turbo it is then passed into the intercooler where it is cooled down before being sent into the combustion chamber.
An open intake might draw in air that is 1-3 degrees warmer than a closed system. This slightly hotter air doesn’t impact the intercoolers ability to adequately cool it. So while the air coming in is slightly hotter, it isn’t any hotter when it goes into the combustion chamber because of the intercooler.
Best Duramax LML Cold Air Intakes
We recommend open air intakes since they provide the best bang-for-the-buck usually. There are dozens of intake manufacturers out there. As long as you get an intake system that has a high quality filter then it really doesn’t matter what intake you get. Just avoid the cheap eBay or Amazon intakes since they usually have crappy China filters. Stick name-brand and they are all pretty much the same.
We’ll provide our favorite open intakes as well as closed intakes for anyone looking for less noise.
1. Best LML Open Intakes: WCFab or Sinister Diesel
Our two exceptions to the “open intakes are cheaper” comment is the WCFab and Sinister Diesel intake systems. These two systems are a bit on the pricier end coming in above $400, but they are top quality systems. Both manufacturers have been around awhile and have strong reputations for quality and performance.
Both the WCFab and Sinister Diesel intake systems are open systems. Neither LML cold air intake has a heat shield, making it a true open system, therefore providing the best power gains. Sinister Diesel manufactures their own air filters while WCFab uses S&B filters.
The one caveat is that the WCFab intake fits all 2011-2016 LML’s whereas Sinister has two different fitments: 2011-2012 and 2013-2016.
If you are looking for a more affordable open intake system then we recommend Gorilla Performance (GDP) which is right around $300.
2. Best LML Closed Intakes: S&B or Banks Power
Similar to the above, Banks Power and S&B are two of the most respected diesel performance brands. Neither offer open intake systems and instead opt for fully-enclosed LML intakes. The S&B system is rather affordable at $350 and the Banks Power comes in slightly pricier around $450.
Since these intakes are closed systems they only provide about 30% airflow improvements, whereas the open systems above offer around 50% more flow. However, since they are enclosed they will be a bit quieter which is nice for anyone who makes frequent long road trips.
LML Duramax Cold Air Intake Upgrade Summary
Whether your LML is completely stock or tuned, an upgraded intake system is always our first recommended mod. In addition to power increases it allows the engine and turbo to breathe better which improves efficiency, gas mileage, and engine responsiveness. When an intake is combined with a tune you can see around 10whp and 20wtq peak power gains, with significantly greater gains throughout the low-end of the power curve.
We prefer open intake systems since they provide more airflow increases and therefore more power gains. However, unless you are shooting for big power gains and plan on upgrading your turbo, a closed intake system will be plenty effective on the LML. WCFab, Sinister Diesel, GDP, S&B, and Banks Power are all well respected intake manufacturers. At the end of the day all of these intake systems are virtually the same and choosing to add a cold air intake is more important than the brand you choose.
Looking for more LML content? Check out our 5 Most Common Duramax LML Engine Problems guide.