Here are the differences. It's more than just a tune..also some heavier duty components....
LLY/LBZ
The LBZ (engine code "D") debuted in late 2006 and continued into 2007 sold only in the "classic" body style. It has an improved engine computer tune that produces increased power and torque over the 2005.5 LLY version of the motor. First appearance of the Duramax in the Express/Savanna vans.
Changes include:
Cylinder block casting and machining changes strengthen the bottom of the cylinder bores to support increased power and torque
Upgraded main bearing material increases durability
Revised piston design helps lower compression ratio to 16.8:1 from 17.5:1
Piston pin bore diameter increased for increased strength
Connecting rod “ I ” section is thicker for increased strength
Cylinder heads revised to accommodate lower compression and reduced cylinder firing pressure
Maximum injection pressure increased from 23,000 psi (1,585.8 bar) to more than 26,000 psi (1,792.6 bar)
Fuel delivered via higher-pressure pump, fuel rails, distribution lines and all-new, seven-hole fuel injectors
Fuel injectors spray directly onto glow plugs, providing faster, better-quality starts and more complete cold-start combustion for reduced emissions
Improved glow plugs heat up faster through an independent controller
Revised variable-geometry turbocharger is aerodynamically more efficient to help deliver smooth and immediate response and lower emissions
Air induction system re-tuned to enhance quietness
EGR has larger cooler to bring more exhaust into the system
First application of new, 32-bit E35 controller, which adjusts and compensates for the fuel flow to bolster efficiency and reduce emissions"
