The information below was taken off of the GM website.

A revised variable-geometry turbocharger also enhances the driving experience of the Duramax 6600. Aerodynamic changes to the turbo's impellers help tailor controlled application of turbo power for seamless and immediate response at full throttle. The turbo, which spins at up to 120,000 rpm, is high-speed-balanced, reducing vibration and resonance - and contributing to the engine's overall smoothness and refinement. The revised turbo also helps reduce emissions, while maximum boost remains at 20 psi.
The comprehensive list of changes and upgrades to the 2006 Duramax 6600 includes:

Cylinder block casting and machining changes to provide increased reliability and durability
Upgraded main bearing material increases durability
Revised piston design helps lower compression ratio to 16.8:1 from 17.5:1
Cylinder heads revised to accommodate lower compression and reduced cylinder firing pressure
Maximum injection pressure increased from 23,000 psi to more than 26,000 psi
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 provide for cooler exhaust gases going 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
The Duramax 6600 also has a new intake air heater to reduce smoke and emissions during cold or light-load driving. The system features a 600-watt grid heater located in the air intake duct, which is triggered automatically by the engine controller. It heats up the incoming air to speed warm-up of the engine.

Changes to the 2006 Duramax 6600 build on a host of improvements introduced for '05 - improvements that bolstered an already strong foundation. The Duramax 6600 features a rigid cast iron cylinder block with induction-hardened cylinder bores; four-bolt, cross-drilled main bearing caps; forged steel, nitride-hardened crankshaft; aluminum pistons with jet-spray oil cooling; aluminum cylinder heads with four valves per cylinder; integrated oil cooler and a charge-cooled turbocharging system. Features, such as easy-access fuel filter and timing gears, reduce maintenance time and effort.

A new, 32-bit engine controller monitors and adjusts the engine's operation. Designed exclusively for the Duramax diesel engine, the controller helps the injectors precisely meter fuel to the cylinders and can compensate for the variability of the injectors and fuel flow. This sophisticated, more powerful controller also can support up to five injections per cylinder and eliminates the need for an engine-mounted drive unit to fire the fuel injectors.

The Duramax 6600 was introduced in 2001 and was developed in a partnership with GM Powertrain and Isuzu Motors. As one of the world's leading manufacturers of diesel engines of all types, Isuzu helped design the basic engine hardware, while engine control systems and electronics were based on GM Powertrain's vast experience with varying climate conditions, driving cycles and ownership expectations.

The Duramax 6600 is assembled at the DMAX facility in Moraine, Ohio, a joint venture between General Motors and Isuzu created specifically to produce diesel engines.

Is this going to be good for the overall performance of the duramax? Are people still going to be able to make big horsepower numbers (after the programmers come out)? Do you think that I should order a new 05 Duramax or an 06 If I want to run fast 1/4 mile times? Any observations or opinions are appreciated.
Thanks
Nate

after reading this i was off to gm's site to find this information. It would appear that these changes are the changes which were made to the motor in order to be placed in the vans at gm. this results in the lower 250hp rating and the 460lb-ft. It is also interesting to note that the limit on the turbo is said to be 20psi. I would imagine all of these things would work together to make the van engine very durable. Most downtuned motors are extremely reliable because they have many parts which are made to stand the pressure and power of the regular version of the motor.

Wouldnt these changes be made to all the duramax engines but with more power/torque in the trucks?

Maybe detuned to that level so it mates with the 4L8xx auto? Allison won't fit?

Hmmm...

The new computer kinda sucks. 2004.5-2005 performance tuning might be orphaned, and new tunes for the new computer might take awhile.

Lower compression would be good for high boost levels. Not good for fuel economy though.

Possibly bigger fuel pump? If they increase volume, not just pressure, more fuel would be available.

Big question, did the turbo get bigger or smaller or same-same?

Model Year '06 pickups will have a 6 speed Allison Transmission instead of the 5 we're used to. The transmission is virtually the same, and most all of the performance products for it will work on the 6 speed variant. It's just a little TCM, and Valve Body magic.

The gear train has had some minor changes such as the helix angle, and the actual ratio's.

Lower CR would be good for higher boost only. And even then, only for power, not efficiency. Lower CR at the same boost=bad all around.

I'm guessing they dropped it for NOx reduction, the only pollutant a diesel cat convertor cannot do anything about.

I'd say that if you need a truck in the next 2 years, try to get an '05 now.

I'd give them a year to iron out the bugs in the new multi-injection tune.

Just Wondering What Everyone Is Running On Diesel Only At The Track. No2 Guys Can Post To.

So will the 2006 bigger better fuel pump fit on the older LLY and LB7?:ro)

Cylinder heads revised to accommodate lower compression and reduced cylinder firing pressure:( That might not be so good.

I'm glad i got an 02 w/ the LB7...Its sounds like a 'COLLECTOR!!!'

lower CR = decreased NOX levels though.

Another kick in the emissions catalyst

im starting to wish i had gotten an 04 instead of an 04.5 since what mcrat said is more than likely whats going to happen, leaving the early lly guys with a low 14 second diesel only 1/4

hopefully my speculation is wrong

Sounds like they are doing this for emissions.

im starting to wish i had gotten an 04 instead of an 04.5 since what mcrat said is more than likely whats going to happen, leaving the early lly guys with a low 14 second diesel only 1/4

hopefully my speculation is wrong

You and me both. I specifically waited for an LLY without considering the ramifications. I assumed the powerband would be wider, and more air up top would be available. So far, nobody seems to know if we have the "superior" turbo or not, but current evidence is pointing to "not".

There will ALWAYS be a way to make bigger peak HP numbers, and quicker ET's. But if the LLY computer gets orphaned, development will slow down (stop) on tuners for that computer, and choices will be fewer.

We do have the superior head design for hotrodding, as the injectors are far easier to access. Banks is using LLY heads on their race engines.

Why do they make such a point about increasing durability in the block and bearings? Would sound better to me if they said they were increasing durability in the injection system. I haven't heard of near as many blocks failing as I have heard of injectors.

I think Bosch would have to come out with a fix for that, not the General.

I'm sure if they(Bosch or GM) knew how to fix the problem, they would.