The 5 Best Duramax LBZ Mods

The LBZ succeeded the LLY engine in 2006 and was short lived, being replaced by the LMM in mid-2007. Some notable changes included an upgraded CP3 fuel pump for higher rail pressure and a lower compression ratio which eliminated issues with connecting rod failure in modified LLY’s. Part of the reason for the short life of the LBZ was emissions – the LBZ engine has an EGR system but lacks all of the other exhaust emissions components.

The LBZ produced 360hp and 650lb-ft. of torque. It’s lack of emissions systems and easy power gains make it common to modify. While these power levels aren’t much compared to the latest diesel engines, a handful of bolt-on upgrades can easily add over 100whp to the LBZ for a pretty low cost.

This guide is going to cover the best bolt-on modifications for the Duramax LBZ. Additionally, we will talk about supporting modifications and power limits of both the engine and its Allison 1000 transmission. We are going to focus on more simple bolt-on mods since things can get really expensive once we push beyond this list.

Duramax LBZ Power Limits

It’s easy to drop a tune and some simple upgrades on the LBZ and make 100whp+ power gains. However, there are some considerations and hurdles to doing so that you will need to consider first.

The biggest hurdle on the LBZ (and all 6.6L Duramax’s) is the Allison 1000 transmission. While it gets stronger and stronger each year, the transmission in the LBZ is only good for about 400whp. Transmission tuning can help make it last a bit longer at higher power levels, but considering a stock LBZ dyno’s about 300rwhp we don’t have much room to play with before hitting the limit of the Allison transmission.

The next limiting factor is the turbocharger and fueling. The stock turbo can reliably handle 500rwhp and can be pushed up around 550rwhp but getting beyond this is going to require a larger turbo. Additionally, a lift pump is always recommended since the LBZ doesn’t have on stock. But furthermore, the injectors will need upgrading when the turbo does. The stock CP3 is good for 625-650rwhp before needing an upgrade.

Lastly, the most expensive flaw with the LBZ is its pistons. While the connecting rod issue with the LLY was fixed, it created an issue with the pistons cracking. The pistons are good up until about 600rwhp but it’s not unforeseen for them to crack above 500rwhp too. Ultimately, getting past 600rwhp or comfortably pushing those power levels without sacrificing reliability is going to require building out the internals.

Power Limit TL;DR

• Allison 1000 transmission needs to be built to make it much past 400rwhp
• Stock LBZ turbo is good for 500rwhp reliably, about 550rwhp when pushed to its limit
• Lift pump is recommended when tuned
• Stock fuel injectors need to be upgraded around 500-550rwhp range
• Stock CP3 fuel pump is good until about 625-650rwhp
• LBZ pistons are prone to cracking at 600+rwhp

Best Duramax LBZ Performance Upgrades

• ECM/TCM tuning
• Cold air intake
• Downpipe
• Full exhaust system (downpipe back)
• Lift Pump (supporting mod)

Mods for 500rwhp+:

• Built Allison 1000 transmission
• Intake Y-Bridge

1) LBZ ECM & TCM Tuning

The biggest power gains on a Duramax diesel come from a tuner. Plug-and-play tuners can easily add around 100whp without need for much else. The majority of the mods discussed after this are to support a tuner and improve reliability when tuned. Running a tune on the highest performance setting without proper mods is a recipe for disaster so follow along for the other mods.

Your two tuning options are getting a plug-and-play handheld tuner that simply plugs into the OBDII port and has pre-made tunes loaded into it. Or getting a custom tune from a tuning shop that is better dialed in to your specific engine.

EFI Live is probably the most robust tuner available for the LBZ. One additional component to this is transmission tuning. Since the Allison transmission is pretty weak, tuning the transmission will help increase reliability and allow you to push around 400rwhp without tearing up the transmission as much as you would without tuning.

LBZ Tuning Benefits

• 30-100+rwhp power gains
• Increases gains from other mods
• Most efficient tuning method ($/hp)
• Improved transmission reliability (with TCM tuning)
• Plug and play install
• Increased gas mileage

2) LBZ Performance Intake

A performance, or cold air, intake is the best mod to combine with a tuner. Tuners increase power mostly by increasing the boost, or psi, that the turbo the turbo is compressing the air to. Supplying the turbo with more air via an upgraded intake is a great way to reduce stress on the turbo and get solid power gains via a more efficient turbo from increased airflow.

Intakes are also good for MPG, throttle response, and turbo spool. We always recommend running an intake when tuned. We also prefer open intakes where the filter is directly exposed to the engine bay since they provide greater airflow increases. More airflow = more power so open intakes are the best on the market in terms of performance.

LBZ Cold Air Intake Performance Benefits

• 10-20whp and 20-30wtq power gains when tuned
• Increased turbo spool
• Quicker throttle response
• 1-2mpg fuel economy gains
• Cool intake sounds
• Increased turbo efficiency

For more information on intake upgrades, checkout our detailed LBZ Intake Upgrade Guide.

3) LBZ Downpipe Upgrade

We are going to discuss a full exhaust system next, but a downpipe is our favorite exhaust mod on the LBZ. It bolts directly to the turbo and therefore has the biggest impact on backpressure and exhaust flow.

The stock LBZ downpipe is poorly designed. It is “crushed” with bends in it that make it really skinny and therefore not great for exhaust gas flow. What this causes is backpressure to build up within the exhaust system which then creates a negative force against the turbo compressor wheel. Ultimately, it makes it harder for the turbine wheel to spin and compress air therefore increasing stress on the turbo and reducing its efficiency.

Downpipe upgrades are the best exhaust mod since they have the biggest impact on backpressure reduction. Therefore, it results in a healthier turbo, better power gains, and also lower engine temps and EGT temps. Definitely a recommended mod when you are tuned and have an intake – the extra air the intake is pulling in makes exhaust gas flow even more important.

Downpipe Performance Gains

• About 15whp and 25wtq
• Reduced exhaust backpressure
• Lower engine temps and EGTs
• Improved turbo efficiency and reliability
• Overall healthier engine + turbo

Best Duramax LBZ Downpipe: Boosted Performance 3″ Downpipe

Price: $219
Buy Here: Boosted Performance Duramax LBZ Downpipe

Boosted Performance makes our favorite LBZ downpipe upgrade on their market. Their downpipe is made of 304 stainless steel which will prevent any rusting issues. Most other downpipes in this price range are made from aluminized steel which will rust over time. Additionally, it features a nice heat shield to prevent excess engine temps.

It’s a larger, non-crushed 3″ design which significantly improves exhaust flow over the factory downpipe. Furthermore, it’s a direct bolt-on part and doesn’t require any additional modifications or tuning. Overall, we think this is the best combination of price, quality, and performance available on the market.

4) Downpipe-Back Exhaust

The best exhaust for a turbo car is technically no exhaust. Fortunately, the LBZ lacks a DPF filter and other exhaust emissions equipment. However, it does still have a diesel oxidation catalyst. We aren’t going to get into the topic of deleting the DOC, but we will get into larger exhaust systems.

A 4″ or 5″ downpipe-back exhaust is the second best way to reduce exhaust backpressure. Since it sits after the DOC and downpipe it isn’t as important of a mod, but it still can help lower EGTs and engine temps even further thru less exhaust backpressure. Ultimately, this mod is more so dependent on whether or not you want a louder exhaust note. They’re pretty affordable and definitely worthwhile if you are okay with a louder exhaust note.

LBZ Full Exhaust Upgrade Benefits

• 5-10rwhp and 10-15wtq power gains
• Lower EGTs and engine temps
• Reduced exhaust backpressure

5) 6.6L Duramax Lift Pump Addition

The LBZ doesn’t have a factory lift pump. Lift pumps essentially help transfer fuel to the high pressure CP3 pump. What this does is reduce stress on the CP3 pump and the fuel injectors. Since increased power requires more fuel tuning an LBZ without a lift pump can cause the CP3 to fail more quickly and can also cause issues with fuel starvation if the pump can’t supply the engine with the fuel that it needs.

Ultimately, this is a supporting mod and one that isn’t going to really add any power. However, it will allow you to supply more fuel to the injectors without the need for an upgraded fuel pump or larger injectors. With a lift pump the CP3 doesn’t need to be upgraded until 600+rwhp.

Additional LBZ Mods

Another great mod is an intake Y-pipe, or Y-bridge alongside an upgraded up-pipe/intercooler piping. These will help with improved intake air flow from the turbo to the intercooler and to the engine. However, this upgrade really isn’t necessary unless you are trying to push beyond the limits of the Allison 1000 and get it built. While it will help improve airflow and therefore help the engine “breath” better you’re going to be looking at close to $1,000 for this upgrade.

Since the Allison is the first limit we hit when modding the LBZ, it is the first major “supporting” upgrade that needs to be made. A built transmission is going to run you $5,000 to $8,000 so it’s a big leap to make. If you aren’t trying to push the LBZ too far then sticking with a tuner, intake, downpipe, and lift pump are really all you need to get some extra enjoyment out of this engine.

Duramax LBZ Mod Summary

The LBZ engine is easy to modify and can hold power pretty well. Simple bolt on modifications like a tuner, intake, and downpipe can get this engine to up around 400rwhp. However, pushing past these power levels is where it gets expensive.

Limiting power factors are the Allison 1000 transmission that can only hold about 400-425rwhp (when tuned). The pistons are known to crack above 600rwhp. The stock turbo is good for 500-550rwhp and alongside a turbo upgrade will require larger injectors. And then pushing to 600rwhp and past is where you will need forged internals and a built motor to keep going.

So while the LBZ can handle some serious horsepower builds it costs a lot of money to get there. For this reason our favorite upgrades are sticking to the simple bolt-ons like a tuner and transmission tuning, a cold air intake, exhaust downpipe, and a lift pump. Some other optional upgrades are a downpipe-back exhaust system and a intake Y-bridge and upgraded intercooler piping. Outside of these mods you are going to be pushing to an echelon that we aren’t covering in this guide.

Ultimately, a few thousand bucks in mods and tuning and can give you a reliable 400rwhp Duramax LBZ. What mods are you currently running and how has your experience been with upgrading the LBZ?