6.6 Duramax: Everything You Need to Know

GM has been putting diesels in their heavy duty trucks since 1982. Granted diesels back then kind of sucked, but none the less they have been doing it for quite some time.

In 2001 they introduced their all new 6.6 Duramax, which was built with the help of Isuzu. Since then they have continued to modify the 6.6 Duramax to suit the current needs.

Before I tell you everything you need to know about the 6.6 D-Max, let’s take a look at the 6.2 Detroit Diesel.

6.2 Diesel

What’s really interesting is how many people absolutely love the 6.2 Detroit engine. I mean, it only makes 160 horsepower, and 285 lb-ft of torque. It’s literally no better than a gasoline engine in terms of horsepower and torque.

Luckily GM knew this and marketed it as fuel efficient alternative to their gasoline engines.

RELATED: 4BT Cummins: Everything You Want to Know

The 6.2 Detroit was used in the AM General HMMWV (Humvee), as well as the CUCV vehicles. I have a slight feeling that its military history is part of the reason so many people are fond of the 6.2 Detroit.A

M General liked the 6.2 Detroit so much that they now run the modern turbocharged 6.5L.

6.6 Duramax: Engine Basics

The 6.6 Duramax engine has been around since 2001. Although it has gone under drastic changes, the architect has remained mostly unchanged. Every year emissions get stricter and it has forced GM to make major changed to the 6.6 Duramax over the years.

Let’s take a look at the D-Max over the years:

6.6 Duramax: LB7

The LB7 introduced in 2001 and continued until mid-2004. The LB7 featured a 32-valve design with high-pressure common-rail direct injection. Unfortunately the LB7 is somewhat remembered by its fuel injector failures and overheating.

GM now warranties these issues but it will always stick with the LB7 name.

Horsepower: 300 hp @ 3,100 RPM
Torque: 520 lb-ft @ 1,800 RPM

6.6 Duramax: LLY

The LLY debuted in 2004, and was produced until the end of 2005. It featured many of the same components as the LB7, but with some improvements. The valve covers were modified to allow easier and cheaper repair to the fuel injectors.

Unfortunately the LLY featured a few new emissions components which diesel lovers seem to hate.

Horsepower: 310 hp @ 3,000 RPM
Torque: 520 lb-ft @ 1,600 RPM

6.6 Duramax: LBZ

Interestingly enough, in 2006 the LLY and LBZ are identical other than the tune. It was slightly detuned, and made less power than it was really supposed to. That changed in mid-2005 when the tune was updated and it made more horsepower than it had before.

Horsepower: 310 hp @ 3,000 RPM
Torque: 605 lb-ft @ 1,600 RPM

6.6 Duramax: LMM

In 2007 GM introduced a new body style for their pickup truck. With it they brought forth the LMM engine. The LMM is similar to the LBZ engine, but with more advanced emissions controls.

The LMM featured a few upgrades with ultimately boosted power to 660 lb-ft of torque.

Horsepower: 365 hp @ 3,200 RPM
Torque: 660 lb-ft @ 1,600 RPM

6.6 Duramax: LML

The LML is a further improvement upon the LMM. Most of the changes are to the emissions system, however there are a few mechanical changes.

Unfortunately the LML does not allow you to easily plug a tuner in and crank the power up like you can with the LMM.

Horsepower: 397 hp @ 3,000 RPM
Torque: 765 lb-ft @ 1,600 RPM


6.6 Duramax: Performance Specs

We’ve pretty much listed off all the performance specs for all 6.6 Duramax engines up to this point. To recap: The LB7 engine had 300 horsepower and an impressive 520 lb-ft of torque by the end of its production life.

The current LML engine has an insane 397 horsepower and 765 lb-ft of torque. The LML is likely nearing the end of its production life, what will the next Duramax hold?

6.6 Duramax: Tuning Potential

This is pretty much the only part that really matters to anyone. Diesels are known for being able to crank out insane power numbers. The 6BT Cummins for example can crank out well over 1,200 lb-ft of torque on stock internals.

But, can the 6.6 Duramax hold its own in the diesel world?

RELATED: 6BT Cummins: Everything You Need to Know

From what I can gather from diesel forums, the factory 6.6 Duramax internals can hold up to about 550rwhp, or 1000 lb-ft of torque at the tire. Thats plenty enough for basically anything you want to do.

Interestingly enough the transmission will only hold to about 400rwhp.

Common Mods

I suppose it’s no use to tell you that the 6.6 Duramax can handle 1000 lb-ft of torque, and then not tell you how to get there. From everything I’ve read on forums, the single best modification is EFI live.

The EFI live system allows you to crank the power of your Duramax way up without having to do any real modifications. Things like exhaust and intake are also very common mods.

Reliability Mods

Diesels are known for being able to chug along for millions of miles. However, with the new emissions systems on modern diesels the longevity of the engine has decreased. The 6.6 Duramax has a few emissions systems that almost everybody ends up deleting:

  1. Diesel Particulate Filter – Also known as DPF, is basically like an extreme catalytic converter. You can thank the kids “rolling coal” for making this become a federally mandated emissions item. However, many people delete it because it is known for essentially destroying your engine prematurely
  2. EGR – This is typically deleted for a few reasons. It’s just another system that can fail. Deleting it makes under the hood look better. If you turn the fuel up, the black soot won’t re-enter your intake system. There are no real performance gains to be had from it, however if you want over 500 horsepower it’ll be a big gain in turbo response and reliability.


Over the last 15 years the 6.6 Duramax has gone through quite a bit of changes. It makes way more power than it used to, but it also has more complex emissions systems. They are all very good engines that will last you 300k miles easily.

Let me know what you think of the 6.6 Duramax in the comments below!

9 thoughts on “6.6 Duramax: Everything You Need to Know”

  1. Good information on the 6.6
    I love my 2001 Chevy Silverado duramax and plan on using her for hauling my travel trailer .
    Possibly tuner in the future.

  2. hi this is George can you help me with the torque speck for Lb7 fuel injector particularly the injector bolt(8mm l bolt) that holds down the injector and the 4 return fuel line banjo bolts. Also can you clarify the difference between lb/ft to lb/in

  3. My 2010 Duramax in my 3500 Silverado I suppose is at its lifes end with 3008,000 miles on it , what probly needs to be done to it short of replacing the engine ?? It runs well , no big problems (yet) what do you think should be done to help it last longer ??

  4. My LB7 is the best thing ive ever driven. At 550hp and 1100ft lbs, its a beast. And real easy to work on too. I love that so many years are nearly the same so finding any info for problems, fixes and parts is probably the easiest of any vehicle on the road. I’ll never get rid of it.

  5. I have a 6.6 dermax 2005 / 2500 crew cab.
    Truck ran fine. Next morning, would start but will quit immediately within a half second.
    Oils fine, fuel tanks full, batteries are fine lights all work.
    Does anyone have any idea what’s wrong

  6. my LBZ that is just bought runs awesome, when cruising it purrs like a kitten, but put the fuel to her and she rolls coal big time and takes off like crazy, my injector levels are within specs but was told all my injectors are bad???? this does not make sense to me, could the plug on the end of the common rail be a culprit or maybe a bad tune?


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