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View Full Version : which 6600 do I have?


eric777
10-23-2007, 18:20
How do I tell which I have i.e. LB7, LLY, LBZ or LMM?

I have a 2004 silverado.
DarylB
10-23-2007, 19:02
Quoted from www.kennedydiesel.com

Engine Identification:

The Duramax engine has evolved from the original LB7 series to the LLY, then LBZ, and now the LMM series. The LB7 was used from 2001 model year until mid 2004 model year. In mid 2004 the LLY series was released. In 2006 the Duramax changed again. The early 2006 engines were still called LLY and the later 2006 and 2007 "Classic" became the LBZ. This creates some confusion as the 06 LLY is distinctively different from the 04.5-05 LLY. The 2006 LLY and LBZ engines are essentially the same when it comes to modifications. The LMM began in the new body style GMT 900 series trucks in 2007. The simplest way to verify which series you have is the VIN# of the truck. The 8th digit is the engine ID and it will either be a 1, 2, D, or 6.

01-04 LB7 is a 1
04.5-05 LLY is a 2
06 LLY is a 2 (uses same mods as LBZ)
06-07 LBZ is a D
07 LMM is a 6 (new body style GMT 900 series)
Example: 1GCHK29143Exxxxxx for LB7 and 1GCHK29245Exxxxx for LLY. It is important to know this as while the engines are essentially the same at the core, the electronics, turbochargers, electronics, and injectors are different among the variants. The 10th place in the VIN number identifies the model year on these vehicles. The example above shows the 2003 model year LB7 and 2005 LLY
eric777
10-27-2007, 17:42
Ok, the 8th digit is #2. So I have the LLY. How does that compare to the others?
Rabbler
10-27-2007, 17:56
Better injector design and more stock power than LB7.
Prone to overheat when worked really hard though.
eric777
10-27-2007, 17:58
What is recommended to boost fuel economy? I averaged 18.9 on the last tank, that was by keeping the rpms to around 1800-2000. Would like to get over 20. Any suggestions?
DarylB
10-27-2007, 18:15
What is recommended to boost fuel economy? I averaged 18.9 on the last tank, that was by keeping the rpms to around 1800-2000. Would like to get over 20. Any suggestions?

Lose weight, slow down, travel downhill & coast as much as possible.
Mark Rinker
10-27-2007, 18:49
Not all LLY's will experience the overheating issues when put to the test.

I owned a 2005 LLY that was hooked to a gooseneck the day it came from the dealer and hauled 9-12K hotshot loads (load and trailer) and similar weight boats (plus wind drag) for 80K miles without incident.

However, the mileage of the '05 was ~15% less than my '01 and '02 LB7s, and didn't seem to have the bottom end power I was used to from the '01.

Most attribute it to the emissions equipment (catalytic converter and EGR) and variable-vane turbocharger switch.

John Kennedy at www.kennedydiesel.com (http://www.kennedydiesel.com) sells a reflashed ECM that optimizes the LLY, improving bottom end towing power, and improving fuel economy.
mark45678
10-28-2007, 09:45
What is recommended to boost fuel economy? I averaged 18.9 on the last tank, that was by keeping the rpms to around 1800-2000. Would like to get over 20. Any suggestions?

your already at the high end of fuel economy for these trucks , about the only two things that may make a light improvement is a live EFI tune that increases the low end power like a tow tune and adds some timing to the motor , poss a turbo back exhaust that removes the cat if you have one . Kennedy diesel is who I would say has one of the nicest tunes for what your looking to do. For what its worth I have never got over 17.5 MPG with any duramax , they are all 4x4 trucks with extra cab or crew cab .
eric777
10-28-2007, 15:30
Lose weight....
That's funny.

Thanks all!
DarylB
10-29-2007, 06:47
That's funny.

Thanks all!

hehe, I didn't mean that personally, just lighten the vehicle load if applicable :)
mschuyler
10-30-2007, 11:06
What is recommended to boost fuel economy? I averaged 18.9 on the last tank, that was by keeping the rpms to around 1800-2000. Would like to get over 20. Any suggestions?
That's good already! I notice the Allison doesn't shift into 6th speed until 55mph, so suggest egg-shell-under-accelerator to 55, stay at 60 mph so RPMs are circa 1500 instead of 1800, and I'll bet you get to the fabled 20. My son-in-law has an 05 LLY and he reports mpg increased once he got over 15K miles, so time and break-in have something to do with it as well. If you experience an increase, please report back here.