The Duramax LB7 was the first engine released under the new 6.6L Duramax platform. The LB7 was considered a strong and stout engine for the time, producing 235hp and 500lb-ft. of torque which was upgraded to 300hp and 520lb-ft. of torque in 2004.
Fortunately, this is a pre-emissions engine and therefore can be easily modified to produce serious power gains. If you’re looking to add a little extra power these 5 Duramax LB7 performance upgrades are a great place to start: intake, tuning, exhaust, intercooler, and downpipe.
Keep in mind that there are a number of LB7 engine problems, such as head gasket and injector failure, that will become more likely to happen when modified.
Duramax LB7 Power Limits
You can get 1,000whp out of an LB7 if you really want to, but it’s not happening on the stock block or internals. The LB7 along with most diesels has a few limiting factors which are fueling, block and internals, and transmission.
- Transmission: 500whp limit for the Allison 1000, requires a built trans to go much beyond it. ZF6 manuals can handle over 600whp with just a clutch upgrade
- Fueling: you’ll need 30% larger injectors at around 525whp which will be good for about 600whp. Above that you will need to upgrade the CP3
- Lift Pump: the LB7 doesn’t have a lift pump, we recommend adding one immediately to help support the CP3 and reduce some stress put on it
- Internals: beyond 600whp is where rods start to get bent so you’ll need to consider internal upgrades at this point
- Turbo: the stock turbo can handle about 525-550whp but EGTs get really hot at these power levels so upgrading the turbo beyond 500whp is recommended
Overall, the power limit on a stock block and stock internals is about 600whp with an upgraded transmission, turbocharger, injectors, and lift pump in addition to other supporting mods mentioned below. If you don’t want to get into all these expensive items then you are capped around 500whp, but a lift pump is still recommended at these levels.
For these reasons, we’re going to focus on basic modifications to get you to the 500whp limit and will save the more advanced mods for separate articles.
If you would rather consume this content via a video, check out our Best Duramax LB7 Mods video below:
5 Best Duramax LB7 Performance Upgrades
- Tuner / Custom Tune
- Cold air intake
- Exhaust System
1) ECM and TCM Tuning
If you are only going to make one LB7 performance upgrade, a tuner is the way to go. Tuners offer the best bang for the buck and can easily add over 100whp. Your two options for LB7 tuning are using an off-the-shelf flash tuner or getting some custom tunes with EFI Live.
Custom tuning will offer the most power gains and the most refined engine performance. However, it is more expensive and limited than using a flash tuner. Custom tunes will need to be adapted and adjusted as performance upgrades are added so we generally only recommend doing it once you have all your other mods equipped. Additionally, if you are just looking for a bit of a performance boost and aren’t shooting for >500whp then I would recommend sticking with a handheld flash tuner.
One additional tuning option is TCM tuning, or transmission tuning. Even at just 500whp it is recommended to have the automatic transmission tuned as it will not hold up for very long on those power levels without tuning. Unfortunately, flash tuners aren’t TCM tuning capable so this will need to be done with EFI Live.
Tuning is a bit more of a complicated subject so I highly recommend you read my guide on Duramax LB7 tuning to learn a bit more and figure out what setup is best for you.
Flash & Custom Tune Performance Benefits
- 100+whp and 300+wtq gains possible
- Least expensive price per horsepower
- Improved fuel efficiency
- Multiple maps for towing, daily driving, performance, fuel economy, etc.
- Enough power for most to not need more mods
2) Cold Air Intake
Our second favorite LB7 performance upgrade is a performance, or cold air, intake. Tuners primarily increase power by increasing the amount of boost or psi produced by the turbocharger. Increasing boost puts more stress on the turbocharger and requires more air since it compresses air to higher pressures. The best way to increase airflow and reduce stress on the turbo is through the addition of an intake.
Intakes are frequently called cold air intakes, although this terminology isn’t necessarily accurate. Since the 6.6 Duramax is turbocharged and has an intercooler, intake temps are not as important as they are on naturally-aspirated engines. All intake systems will keep the stock intake location but simply utilize a larger air filter to increase the amount of volume entering the engine.
Open vs. Closed LB7 Intakes
You’ll find two different types of intake designs: open and closed. Open intakes have the filter directly exposed to the engine bay. On closed intakes the filter is housed within a box. Open intakes provide the biggest increase in airflow and therefore the most performance benefits. For this reason, we prefer and recommend open intakes. Closed intakes reduce intake air temps, but as mentioned above this doesn’t really matter.
One of the big considerations between the two is noise. Open intakes provide a lot more intake whooshing noises which can make them annoying for long road trips. Closed intakes are quieter. While open systems provide more airflow and performance it really isn’t a huge deal until you are shooting for huge power levels. Closed intakes will provide enough airflow increases over the stock intake to handle all of the mods on this list.
Ultimately, if you care more about intake noise get a closed intake. If you care more about performance or what more noise, go open.
Intake Upgrade Performance Benefits
- 50%+ increase in airflow
- Reduced turbo stress
- Increased turbo spool and efficiency
- Better throttle response
- Decreased EGTs
- Better fuel economy
Best Closed Intakes: Banks Power and S&B
Best Open Intakes: HSP, aFe, WC Fab
3) 4-inch Downpipe-Back Exhaust System
Next on our list is a downpipe-back exhaust system. We cover downpipes as the #5 best LB7 performance upgrades on our list but upgrading the downpipe is also common to do while upgrading the exhaust system. Unlike modern diesels with diesel particulate filters and all those emissions goodies, the LB7 is pretty much emissions free. This is good for performance but might make you think an exhaust upgrade isn’t worth it.
Despite not having a lot of emissions equipment, the stock LB7 exhaust system is still very restrictive. Upgrading to a 4″ or even 5″ system will drastically reduce exhaust backpressure as well as exhaust gas temps (EGTs).
The reduced EGTs result in improved turbo efficiency and ultimately more horsepower and torque. The only pre-2004 LB7’s that had catalytic converters were trucks sold in California. Therefore, upgrading the exhaust system to one without any cats is legal in all states except for California. Power gains and benefits are even greater if you do have a Cali truck with the cats and decide to remove them.
There are a lot of different considerations for upgrading the LB7 exhaust – such as material, piping diameter, and mufflers. My recommendation is to get a 4″ aluminum exhaust without a muffler if you are on the stock turbo and to get a 5″ if you have an upgraded turbo. Steel has a lot of drone and is more expensive and mufflers are restrictive and also more expensive. Additionally, I always recommend a downpipe with an exhaust (but it is a bit harder to install).
Exhaust System Benefits
- 20-30whp and 50-60wtq gains when combined with downpipe
- Virtually zero backpressure
- Better turbo spool and efficiency
- Better exhaust note
4) Intercooler Upgrades
LB7’s are prone to head gasket failure which is predominantly caused by engine temps. One of the best LB7 mods to reduce engine temps is an upgraded intercooler. Unfortunately this is the most expensive performance upgrade on our list but also one of the best for engine reliability.
Intake air gets heated up as it passes through the intake system and turbocharger. The intercooler cools the pressurized air before it enters the combustion chamber. If you are running a tune and an intake, you are bringing significantly more air into the system. This increase in airflow can easily overwhelm the intercooler and cause heat soak.
Intercoolers do provide some power gains but their biggest benefit is also preventing power loss from excess engine temps. Back to back pulls or frequent aggressive driving can overwhelm the stock intercooler and cause it to not effectively cool air before entering the engine. This results in hot air passing into the engine and reducing power and performance in addition to reliability.
An upgraded LB7 intercooler results in more constant performance, lower EGTs, better reliability, and an overall healthier engine. Despite it being on the more expensive end, it’s one of our favorite LB7 performance upgrades.
Upgraded Intercooler Benefits
- More consistent performance, no performance loss from heat soak
- Lower EGTs
- Improved engine reliability
- 30%+ increase in airflow and capacity
- Increased fuel economy
Best LB7 Intercooler: Banks Techni-Cooler
5) 3-inch Downpipe
A downpipe comes in last on our list only because it’s very difficult to install without pulling the trans and requires relocation of the trans dipstick. A downpipe bolts up directly to the turbocharger and the downpipe-back exhaust system. The stock downpipe is highly restrictive.
Since the downpipe is attached to the turbo the restriction creates a lot of backpressure. Backpressure for a turbo is bad. It creates force against the turbo and makes it more difficult to spool therefore reducing efficiency and turbo reliability. Removing this restriction reduces backpressure and therefore improves turbo efficiency and turbo spool.
While the downpipe is challenging to upgrade it’s definitely the most important part of the exhaust to upgrade. Running a bigger exhaust but keeping the small, crushed, and restrictive downpipe will minimize the performance gains and EGT reduction you get out of an exhaust upgrade.
Downpipe Upgrade Benefits
- 10-15whp power gains
- Reduced exhaust backpressure
- Decreased EGTs
- Improved turbo efficiency and reliability
- Faster turbo spool
- More throttle and turbo response
PPE 3″ LB7 Downpipe Upgrade
At only $170 this is the best bang-for-the-buck on the market. It will bolt-up directly to the 4″ MBRP exhaust that I recommend as well.
The LB7 Duramax is capable of handling about 500whp without the need for very expensive upgrades. Our 5 favorite mods are a tune, intake, exhaust, downpipe, and intercooler which can easily get the LB7 to the 500whp mark for only a few thousand dollars.
To surpass the 500whp mark you will need to build out the transmission, upgrade the turbo, add larger injections, and add a lift pump. Getting to the 600whp mark is going to cost somewhere around $15k for automatics, and $10k for manual transmissions. Surpassing these levels will require a built engine and other serious upgrades.
The LB7 has weak injectors and head gaskets. Considering these engines are getting quite old, adding performance mods is going to increase the likelihood of failure if these components haven’t already been replaced. Additionally, modifying any old eninge increases the likelihood of internals failures, water pump failures, cooling system problems, and so on.
Overall, the LB7 is mod-friendly up to the 500whp mark, which can be reached for around $3k. Above these power levels the engine becomes very expensive to modify in addition to decreasing reliability a significant amount.