6.6L Duramax LLY

The 6.6L Duramax LLY represents the Duramax 6600 engine platform's transition to modern emission controls, meeting stricter requirements in the U.S. while updating the platform to maintain competitive. In addition to an exhaust gas recirculation (EGR) system becoming standard on all models, the LLY ditched the LB7's fixed geometry, wastegated turbocharger for a Garrett variable geometry model. The variable geometry, or variable vane turbocharger increased throttle response by reducing turbo lag and set the stage for increased horsepower and torque; this turbocharger would be used through the 2016 model year LML.

6.6L LLY Duramax Engine Specs, History, & Information

For the 2006 model year the 6.6L Duramax LLY underwent a slew of changes including structural improvements and increased horsepower/torque ratings. The 2006 LLY is mechanically identical to its replacement, the LBZ, but the LBZ is calibrated uniquely from the LLY. Some resources categorize the 2006 LLY as a LBZ, however GM always made the distinction between the two and thus we classify them as two separate, albeit similar generations of the 6.6L Duramax. One of the most prominent changes was a new valve cover design that no longer hid the fuel injectors, improving serviceability and addressing the injector concerns related to the previous LB7 generation's issues. A full list of the 2006 LLY's changes can be found below.

The Duramax LLY phased out the LB7 during the 2004 model year, thus 2004 vehicles can be found with either the LLY or the earlier LB7. The most definitive way to distinguish between the two generations is to look up the 8th digit of the vehicle identification number (VIN); this number is unique to each engine generation. A 2004 model year LB7 will have an 8th digit "1" while a 2004 model year LLY will have an 8th digit "2". Similarly, a 2006 model year LLY will have an 8th digit "2" while a 2006 model year LBZ will have an 8th digit "D". Parts compatibility between generations of the Duramax diesel is not always high and thus it's important to identify the correct engine on the phase-in/phase-out model years where two engine options briefly coexisted.

The 6.6L Duramax LLY was rated at a peak 310 horsepower in trucks equipped with the Allison 1000 automatic transmission and 300 horsepower where the engine was mated to the ZF S6-650 manual transmission. Peak torque for automatic transmission equipped trucks was 605 lb-ft while manual transmission equipped trucks were detuned to 520 lb-ft. The horsepower and torque ratings on the ZF equipped trucks was identical to those found on all LB7 (previous generation) powered trucks; as a result, manual transmission equipped trucks are somewhat rare and not greatly sought after.

6.6L LLY Duramax Specs

Engine Family:

6.6L Duramax diesel (Duramax 6600)

RPO Code:


VIN Code:

2 (8th digit of VIN)

Assembly Site:

DMAX engine plant, Moraine, Ohio

Applications/Production Years:

2004 - 2006 Chevrolet Silverado 2500 HD, 3500 HD
2004 - 2006 GMC Sierra 2500 HD, 3500 HD
2004 - 2006 Chevrolet Kodiak
2004 - 2006 GMC TopKick
2006 Hummer H1


6.599 liters (6.6 liters nominal), 402.62 CID (403 CID nominal)


90 degree V-8

B10 Life:

Not specified

B50 Life:

Not specified


4.055 inches (103.00 mm)


3.897 inches (99.00 mm)

Bore/Stroke Ratio:

1.04 (marginally oversquare)

Compression Ratio:

2004 - 2005 model years

17.5 : 1

2006 model year

16.8 : 1

Firing Order:


Cylinder Numbers:

6.6 Duramax cylinder numbers and locations

Cylinders 1, 3, 5, and 7 are located on the passenger side bank
Cylinders 2, 4, 6, and 8 are located on the driver side bank

Engine Block Material:

Cast gray iron, induction hardened, deep skirt engine block

Cylinder Head Material:

Cast aluminum alloy

Injection System:

Direct injection
Bosch high pressure common rail system, piezoelectric fuel injectors
Bosch CP3 (CP3.3) injection pump
23,000 psi max injection pressure for 2004 & 2005 models
26,000 psi max injection pressure for 2006 models


Turbocharged, air-to-air intercooler
Water-cooled Garrett GT3788VA variable vane turbocharger (VVT)

Minimum Cylinder Pressure:

300 psi (minimum compression test pressure)

Reciprocating Assembly:

Fracture split forged alloy steel connecting rods
Nitrided forged steel crankshaft
Forged steel camshaft
Cast iron main bearing caps


Overhead valve (OHV), standard cam-in-block, mechanical roller lifters
4 valves per cylinder (32 valve)

Cold Start Aid(s):

Traditional glow plug system, 1 per cylinder

Engine Oil Capacity:

10 quarts with oil filter change

Engine Oil Spec:

See viscosity chart at 6.6L Duramax LLY service guide

Lube Oil Filter P/N:

ACDelco PF2232

Fuel [1]:

#2 low sulfur diesel fuel preferred (includes winterized blends)
#1 low sulfur diesel fuel acceptable in cold weather
Max B5 biodiesel blends (5% biodiesel, 95% petroleum diesel)

Peak Horsepower:

With Allison automatic transmission

310 hp @ 3,000 rpm

With ZF 6 speed manual transmission

300 hp @ 3,000 rpm

w/ LRY power option (Kodiak/TopKick only)

210 hp @ 2,750 rpm

w/ LRX or LPD power option (Kodiak/TopKick only)

300 hp @ 3,000 rpm

Peak Torque:

2004 - 2006 models w/ manual transmission

520 lb-ft @ 1,600 rpm

2006 models w/ automatic transmission

605 lb-ft @ 1,600 rpm

w/ LRY or LRX power option (Kodiak/TopKick only)

520 lb-ft @ 1,600 rpm

w/ LPD power option (Kodiak/TopKick only)

605 lb-ft @ 1,600 rpm

Idle Speed:

~ 680 rpm @ operating temperature

Governed Speed:

3,250 rpm (electronically governed)

Emissions Equipment:

Exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC)

Coupled Transmissions:

Allison 1000 automatic, ZF S6-650 6 speed manual

Engine Weight:

Approx. 835 lbs

Engine Dimensions:


Approx 30.0 inches


Approx 30.0 inches


Approx 32.0 inches

[1] - Ultra low sulfur diesel (ULSD) supersedes low sulfur diesel (LSD) specification in the United States, original OE recommendations listed.

6.6L LLY Duramax Horsepower & Torque Curves

6.6L Duramax LLY horsepower and torque graph, automatic transmission

6.6L Duramax LLY horsepower and torque graph (with Allison 5 speed automatic transmission)

6.6L Duramax LLY horsepower and torque graph, with manual transmission

6.6L Duramax LLY horsepower and torque graph (with ZF 6 speed manual transmission)

2006 Model Year 6.6L LLY Duramax Changes, Updates, & Revisions

The 2006 LLY is mechanically identical to the later LBZ and the usage of the LLY RPO code for the 2006 model year often causes confusion. The 6.6L Duramax LBZ was designed and developed with the goal of launching during the 2006 model year. However, delays in the EPA emissions certification process meant that GM would not be able to offer the LBZ as early as intended. Therefore, the newly designed LBZ was simply operated on the previous generation LLY's calibration during the 2006 model year until the LBZ engine calibration was cleared through the emissions certification process. GM had always distinguished between the LLY and the LBZ, however you may find that many resources combine the LLY and LBZ into a single platform when referring to the 2006 model year.

The updated 2006 model LLY would ultimately transition to become the LBZ, save the LBZ's new calibration that offered higher peak horsepower and torque output. The 2006 model year LLY changes include:

• New engine block casting and machining procedures adopted to increase block strength and integrity.

• New main bearing design (including material changes) providing increased longevity, reliability, and higher resilience to engine stresses.

• Updated piston design with larger wrist pin diameter, compression ratio reduced to 16.8 to 1 (from 17.5 to 1).

• Revised cylinder head design, related to lowered compression ratio.

• Updated connecting rod design with a thicker I-beam cross section.

• Maximum fuel injection pressure (nozzle pressure) increased from 23,000 psi to 26,000 psi, fuel system revisions include fuel pump, lines, and common rails.

• Revised 7 hole fuel injector nozzle design and altered fuel injector positioning; fuel injector spray pattern was directed onto the tip of the glow plug in order to provide more efficient and quicker engine starting and reduce emissions during cold starts.

• New "fast heat" glow plugs.

• Updated, more efficient variable geometry turbocharger (VGT, also variable vane or VVT) design reduced turbocharger lag and improved engine responsiveness.

• Revised air induction system to reduce engine noise.

• Larger exhaust gas recirculation (EGR) cooler provided more efficient cooling and was less prone to clogging.

• Intake air heater introduced in order to reduce emissions during engine warm-up and allow engine to reach operating temperature more rapidly.

The goal of the changes was ultimately to update the 6.6L Duramax engine platform so that it could meet future emissions, efficiency, and performance goals.