6.6L LLY Duramax Specifications and Information

Found yourself wondering, maybe even daydreaming about the 6.6L LLY Duramax? Well, you aren’t alone! These vehicles are known for their reliability, power, and lower emissions. But what else is there to say about the 6.6L LLY  Duramax?

Well, today we are going to find out! We will be looking at the specifications and all relevant information about the 6.6L LLY Duramax so that you can become a Duramax expert!

Keep reading to see the 6.6L LLY Duramax specifications and information!

Editor’s Note: Be sure to also check out our answers to What is the best tire size for Jeep Wrangler? and What are the best all terrain tires for Overlanding?

Background Knowledge

Before we get into all the important facts, let’s look at the background and history of the 6.6L LLY Duramax. This vehicle is the 2nd generation of Duramax, referred to as the LLY.

They are reliable and powerful trucks that come without the high emissions we see on modern Diesel trucks. They also do not feature injector failures that we frequently see on LB7 trucks.

LLY Duramax trucks do have issues consistent with overheating. Duramax has added a vane turbocharger and EGR system in the hope of alleviating these issues. Now that we have had a little history lesson let’s get into the specs of the truck!


Manufactured years: 2004-2006
Engine design: 6.6L 90 degrees V8 turbocharged diesel
Transmission: 2004-5: five-speed auto Allison transmission.

2006: six-speed auto Allison transmission

Vin identification (8th digit): 2
Displacement: 6.6L (403 cubic inches)
Bore: 4.055” (103 mm)
Engine weight: 835 lbs
Engine oil capacity: 10 quarts including filter
Fuel tank size: Short beds: 26 gallons

Long beds: 34 gallons

Fuel: Diesel
Fuel injection: Direct injection high-pressure common rail with  bosch CP3 injection pump
Stroke: 3.987” (99mm)
Block material: Cast iron
Cylinder head: Cast aluminum
Crankshaft: Forged steel
Connecting rods: Forged steel
Firing order: 1-2-7-8-4-5-6-3
Compression Ratio:  2004-5: 17.5:1

2006: 16.8:1

Turbocharger/air: GARRETT GT3788VA VARIABLE VANE Turbocharger And Intercooler
Valvetrain: Overhead Valve (OHV) 4 Valves per cylinder (32V)
Max engine speed: 3,250 RPM
Horsepower: 310 horsepower
Torque:  2004-5: 520 lb/ft at 1,600rpms

2006: 605 lb/ft at 1,600rpms

That’s all the specifications covered! As you can see, the 6.6L LLY Duramax has lots of great features that set it apart from other trucks. It features sturdy construction in the engine and holds a decent amount of fuel. Let’s take a closer look at these features and how they impact the 6.6L LLY Duramax performance now.


Arguably the most important part, how does the 6.6L LLY Duramax perform? As you will have seen in our little specs chart, the Duramax features a turbocharger. What you might not know is that it is one of the largest turbochargers found on Duramax’s! This turbocharger allows the truck to have incredible horsepower and adds to the torque if necessary.

6.6l lly duramax performance

It performs exceptionally well, although the LLY can become susceptible to gasket failures. You will need to keep an eye out for this and be sure to repair it or consult a mechanic immediately.

You will also need to take care if you use an EFI Live or another tuner to tune your LLY. It is a good idea to invest in an ARP head stud kit to avoid any issues during your truck’s maintenance.

You can upgrade the performance of your LLY Duramax, too, if you wish; most commonly, owners want to add larger wheels or tires. Be sure to check out our thoughts on this later on!

How heavy can you tow?

The towing capacity of the LLY Duramax depends on the model purchased, as there are slight variations. As a general guide, you can apply a maximum of 12,000lbs to be towed.

The capacity of a 5th wheel tow varies between the years and configuration of the cabs. These numbers for fifth-wheel tows are between 15,000lbs and 16,700lbs. Be sure to check the specific capacity based on the year of your truck.

Dulles and two-wheel drive models will also have different tow ratings. These tend to be higher than the ones listed above. There is also a variation with 4wd  models as they offer a lower capacity when using a fifth-wheel tow.

Any issues?

Although it may be the truck of your dreams, it is not without its kinks. The injector issues seen on the LB7 Duramax aren’t present on the LLY, but there are other issues that you need to be aware of.

There is no lift pump included, so you will need to consider purchasing your lift pump. Fass or Air Dog are excellent options that will work well with the LLY.  A lift pump will offer plenty of fuel and enhanced fuel filtration compared to your stock fuel filter. These features protect parts of the fuel injection pump and fuel injectors from damage and save you costly repairs down the line.

A common issue with the 6.6L LLY Duramax is overheating. The small radiator and a lower coolant capacity allow your truck to get hot quickly! Combined with the restricted airflow, it does not take long for you to feel the heat!

You may want to make changes to the LLY Duramax as you would with other trucks from Duramax. A common area is the truck’s front, where owners usually want to add bigger tires or larger wheels. Well, it is not so simple with an LLY Duramax!

Despite the independent front suspension (IFS suspension) providing a comfortable and enjoyable ride, it is not as stout as a straight axle. You can use other products to upgrade your Duramax’s front end, such as Kryptonite or Cognito. It might be worth doing some further research or consulting a mechanic if you plan to make any changes!

Final Word

As you can see, there are lots of great features on the 6.6L LLY Duramax. The engine is of stable construction, and the truck gets decent mileage. The turbocharger is still the largest in Duramax trucks’ use to provide you with the performance you crave!

Some issues will need to be addressed, but apart from the heating and a lack of a lift pump, we think you will be pleasantly surprised with the 6.6L LLY Duramax!