Duramax 6.6L LLY V8
Horsepower
310 hp
Torque
605 lb-ft
Years produced
2004–2006
Aspiration
Turbocharged
- Configuration
- V8, 6.6 L
- Aspiration
- Turbocharged
- Builder
- DMAX Ltd.
- Designers
- Joint venture of GM and Isuzu (DMAX); engine blocks supplied by Fritz Winter
- Years
- 2004–2006
Offered in: Chevrolet Chevrolet Silverado 2500HD, Chevrolet Chevrolet Silverado 3500, GMC GMC Sierra 2500HD, GMC GMC Sierra 3500
The LLY replaced the LB7 in mid-2004 with a variable-geometry turbocharger and an EGR valve, GM's first step toward emissions compliance for the Duramax. It was rated at 310 hp and 605 lb-ft, a notable torque increase over the LB7. It was offered in Silverado and Sierra 2500HD and 3500 pickups with the Allison automatic or a manual. It was superseded by the LBZ in 2006.
What made it successful
It raised torque considerably while adding emissions equipment, and it kept the common-rail design of the LB7.
Market position
Its 605 lb-ft rating was a large step up within the segment at the time. Sourced comparisons with Ford and Ram are not yet included.
Rebuild Potential
Tier BEditorial opinion.
The LLY shares most of its parts and knowledge with the LB7 and LBZ, so support is excellent. It ranks below them because the cooling weakness is a real risk and the emissions hardware (EGR, variable-geometry turbo) adds complexity. With the known cooling fixes done, it is a sound rebuild candidate.
Best year ranges
- 2005-2006: Later trucks are usually considered better than the earliest 2004.5 builds because of cooling and airflow complaints; confirm which changes GM made when.
Known weak points
Overheating under load, linked to airflow and cooling capacity, and in some cases head gasket failure.
Common fix: Improve airflow with an LBZ-style intake mouthpiece, upgrade the radiator or cooling stack, and refresh the coolant.
Common upgrade categories
- Cooling stack and intake mouthpiece upgrades
- Head gasket and head stud replacement
- Injector and fuel system service
- Transmission and exhaust upgrades within local legal limits
Keep the emissions equipment the truck was built with. Removing or defeating it on a vehicle originally equipped with it is illegal under federal law. Rules vary by state (for example California/CARB), so check local law and model-year requirements before modifying.
Sources
- Duramax V8 engine (Wikipedia) (accessed 2026-09-18)
- Chevrolet Silverado, first generation (Wikipedia) (accessed 2026-09-18)