6.6L LMM Duramax Engine Specs, History, & Information
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 |
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| 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 | |
| Cylinder Numbers |  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 |
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| Engine Block Material | Cast gray iron | |
| 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 26,000 psi max injection pressure |
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| Aspiration | Turbocharged, air-to-air intercooler Water-cooled Garrett GT3788VA variable vane turbocharger (VVT) |
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| 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 |
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| Valvetrain | Overhead valve (OHV), standard cam-in-block, mechanical roller lifters 4 valves per cylinder (32 valve) |
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| 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) | |
| 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 | |
| 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 | |