2004-2005 Duramax LLY Engine

2004-2005 Duramax LLY Engine

2004–2005 Duramax LLY 6.6L Diesel Engine – Mid-Generation Power, Proven Performance, Towing Confidence

The Duramax LLY engine, available in select 2004–2005 Chevrolet Silverado HD and GMC Sierra HD trucks, represents a key evolution in GM’s legendary 6.6L V8 turbo diesel lineup. Known for its blend of performance, towing capability, and improved engine management, the LLY is a favorite among diesel enthusiasts and heavy-duty truck owners seeking a reliable and powerful engine with modern features and impressive durability.

The LLY engine builds on the strong foundation of the previous LB7 while introducing several key upgrades. Most notably, it was the first Duramax to feature a variable geometry turbocharger (VGT), providing faster spool-up, better throttle response, and superior towing performance, especially at lower RPMs. This design also helped reduce turbo lag and improve drivability under load.

Another significant improvement was the switch to external EGR (Exhaust Gas Recirculation), allowing for better emissions control without significantly compromising performance. The LLY also introduced a new injector design—one that resolved many of the premature failure issues seen in the earlier LB7 models. These injectors are mounted outside the valve covers, making service and maintenance far easier and less costly.

2004-2005 Duramax LLY Engine Key Engine Specs:

• Engine code: LLY

• Displacement: 6.6L (403 cubic inches)

• Configuration: 90° V8 turbo diesel

• Fuel system: Common rail direct injection (Bosch CP3)

• Turbocharger: Garrett VGT (variable geometry turbo)

• Horsepower: ~310 hp @ 3,000 rpm

• Torque: ~605 lb-ft @ 1,600 rpm

• Compatible models: 2004.5–2005 Silverado 2500HD/3500 & Sierra 2500HD/3500

Whether you’re replacing a worn-out powerplant, doing a full rebuild, or sourcing a complete swap for your project truck, the 2004–2005 LLY Duramax delivers a strong balance of performance, reliability, and tunability. It’s an excellent platform for towing, work, or performance upgrades and remains one of the most sought-after diesel engines in GM’s heavy-duty lineup.