6.6L Duramax LMM

6.6L LMM Duramax Engine Specs, History, & Information

The 6.6L Duramax LMM was introduced roughly mid-model year for 2007, phasing out the previous generation LBZ completely by the start of the 2008 model year. The engine is largely identical to the LBZ platform, but met stringent Federal emissions standards that required the integration of an exhaust aftertreatment system. This new aftertreatment system relied on a diesel particulate filter (DPF) to lower particulate (soot) emissions and employed a variety of sensors to perpetually monitor the system and periodically initiate the regeneration sequence, at which point hydrocarbons in the DPF are effectively incinerated into more favorable exhaust byproducts.

Poor fuel economy and DPF clogging were amongst the earliest and most prominent concerns regarding the 6.6L Duramax LML. It's noteworthy that this was not a GM issue - these complaints were felt industry wide as Ford and Dodge rolled out their own DPF equipped platforms. Excessive fuel dilution would later become a major concern as the post-injection sequence allows raw, unburned fuel to pass through the combustion chamber during regeneration. The diesel particulate filter is designed to capture "large" particulates and retain them until they can be burned into smaller particles that will pass through the filter system. This system requires periodic maintenance in the form of a regeneration cycle. Regeneration is split into two types, passive and active.

Passive regeneration is an inconspicuous process and is always invisible to the driver. During passive regeneration, operating conditions (primarily exhaust gas temperature) are correct for particulate matter to be reduced through incineration in the DPF. This requires no intervention by the driver or engine management system. Driving at a constant highway speed for long periods of time, for example, is likely to promote the conditions under which passive regeneration may occur. Idling, stop-and-go traffic, and low speed operation are highly unlikely to permit passive regeneration at any equitable rate.

Active regeneration occurs when the DPF is reaching its peak capacity and requires cleaning. Active regeneration is commanded by the ECM when the differential pressure measured across the DPF (pressure difference between the inlet and outlet of the filter) reaches a certain threshold, prompting the active regeneration process to be initiated. During active regeneration raw fuel is introduced into the exhaust stream where it burns in the DOC and increases the exhaust gas temperature. This process continues until the particulate matter captured in the DPF is incinerated, reduced in size, and exits the exhaust system. The ECM will end the active regeneration cycle once the differential pressure measured across the DPF reaches a minimum threshold or the cycle is canceled by turning the engine off. Active regeneration can be somewhat invasive and is detectable by the driver. In addition to a "clean exhaust filter" message displayed in the instrument cluster, active regeneration may cause an elevated idle, reduced performance/response, light burning odor, and a change in engine sound. When active regeneration is initiated or detected, drivers should continue to operate the vehicle at a speed above 30 mph until the process has completed.

The Achilles' heal of the regeneration process is the method by which fuel is introduced into the exhaust stream. A post-injection technique is employed on the LMM, which injects fuel into the combustion chamber during the exhaust stroke. The unburned fuel is quickly carried out of the combustion chamber, but this technique often contributes to relatively high fuel dilution rates due to the fuel's tendency to stick to the cylinder walls where it is swept into the crankcase by the following stroke of the piston.

The 6.6L Duramax LMM featured only a small horsepower and torque increase over its predecessor. It was available through the 2010 model year and was replaced entirely by the LML for 2011, which features an even more advanced exhaust aftertreatment system requiring the industry's [then] new diesel exhaust fluid (DEF).

6.6L LMM Duramax Specs

Engine Family:

6.6L Duramax diesel (Duramax 6600)

RPO Code:

LMM

VIN Code:

6 (8th digit of VIN)

Assembly Site:

DMAX engine plant, Moraine, Ohio

Applications/Production Years:

2007.5 - 2010 Chevrolet Silverado 2500 HD, 3500 HD
2007.5 - 2010 GMC Sierra 2500 HD, 3500 HD
2007.5 - 2010 Chevrolet Express 2500, 3500, 4500
2007.5 - 2010 GMC Savana 2500, 3500, 4500

Displacement:

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

Configuration:

90 degree V-8

B10 Life:

Not specified

B50 Life:

Not specified

Bore:

4.055 inches (103.00 mm)

Stroke:

3.897 inches (99.00 mm)

Bore/Stroke Ratio:

1.04 (marginally oversquare)

Compression Ratio:

16.8 : 1

Firing Order:

1-2-7-8-4-5-6-3

6.6L Duramax LMM cylinder numbers

Engine Block Material:

Cast gray iron

Cylinder Head Material:

Cast aluminum alloy

Injection System:

Direct injection
Bosch high pressure common rail system
Piezo electric fuel injectors
Bosch CP3 (CP3.3) injection pump
26,000 psi max injection pressure

Aspiration:

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

Valvetrain:

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 LMM service guide

Lube Oil Filter P/N:

ACDelco PF2232

Fuel:

Ultra low sulfur diesel (ULSD), biodiesel blends up to B5 (5% biodiesel, 95% petroleum diesel)

Peak Horsepower:

Silverado/Sierra

365 hp @ 3,200 rpm

Express/Savana

250 hp @ 3,200 rpm

Kodiak/TopKick w/ LRX power option

300 hp @ 3,000 rpm

Kodiak/TopKick w/ LYE power option

330 hp @ 3,000 rpm

Peak Torque:

Silverado/Sierra

660 lb-ft @ 1,600 rpm

Express/Savana

460 lb-ft @ 1,600 rpm

Kodiak/TopKick w/ LRX power option

520 lb-ft @ 1,600 rpm

Kodiak/TopKick w/ LYE power option

620 lb-ft @ 1,600 rpm

Idle Speed:

~ 680 rpm @ operating temperature

Governed Speed:

3,450 rpm (electronically governed)

Emissions Equipment:

Diesel particulate filter (DPF), diesel oxidation catalyst (DOC), exhaust gas recirculation (EGR)

Coupled Transmissions:

Allison 1000 6 speed automatic

Engine Weight:

Approx. 835 lbs

Engine Dimensions:

Length:

Approx 30.0 inches

Width:

Approx 30.0 inches

Height:

Approx 32.0 inches

Page Information

Last update: 11/19/2021

Copyright: Diesel Hub (dieselhub.com), all rights reserved

Sources: General Motors original spec sheets, brochures, 2007 to 2010 model year Silverado/Sierra owners manuals and Duramax diesel supplements, and archived data (gm.com, gmpowertrain.com, gmfleet.com, and in print form)