Duramax Engine 6.6L Duramax User Manual
Rebuilding The 6.6L Duramax Diesel
By Roy Berndt
It was really no surprise, since GM had single-handedly alienated the American buying public
against the diesel engine beginning back in the late ’70s and early ’80s with the 5.7L V8 and
4.3L V6 diesel engines that were, let’s just say, “less than stellar.” While there’s no point now in
rehashing mistakes of the past, the 6.2L and 6.5L diesels had continued on in a similar tradition,
even though the 6.5L was used in the HUMVEE for the military.
In order to have a winning truck this time, GM needed to have a winning diesel powertrain. The
General already had two strikes and a third may have put GM out of the diesel pick-up market
altogether.
A small group of stakeholders led by the Planning Group reviewed proposals from numerous
possible diesel engine manufacturers for the all-new truck. The decision was reached to go with a
proposal from one of GM’s partners – Isuzu Motors LTD, a company founded in 1916 and, with
a long history of successful diesel technology, recognized worldwide as a leader in diesel
engines. The proposal was developed as a part of a strategic 90-day study conducted by Isuzu
and GM, relative to Isuzu’s role in the GM Global enterprise.
While Isuzu’s plan called for a “Clean Sheet” brand new engine design that would not be ready
until 2003, GM’s new HD pickup truck was going into production in late 2000. After high-level
executive meetings, Isuzu found a way to pull ahead the timing to meet GM’s needs. In May
1997, the project team was established under the leadership of Jim Hogan, GM Truck Group;
Yoshihiro Tadaki, Isuzu; and Jim Kerekes, representing GM Powertrain.
The project was codenamed “B908” (bridge between U.S. and Isuzu, 90-day study and 8cylinders). This would be the first V8 diesel engine Isuzu ever designed for the U.S. HD pickup
market. Isuzu was responsible for the base engine design and GM was responsible for the
integration of the engine into the vehicle. The GM Powertrain – Romulus Engineering Lab
became the center of activity in the U.S.
The first running B908 engines were available in early 1998 in Japan and soon were installed in
mule vehicles in the U.S. to begin the final development. The B908 Team used the 13-hour time
difference to their advantage. They would videoconference late in the day U.S. time while Japan
would work on the issue during their day and when the U.S. team came in the next morning,
have another videoconference to review and the US would work during their day while it was
Japan’s night. It was truly 24/7 development.
The GM-Isuzu 90-day study established the plan to manufacture the new engine: a joint venture
company named DMAX Ltd. (signifying the diesel engine and maximum power, cleanliness and
fuel economy) was established in September, 1998 in Moraine, OH. A new 650,000 sq. ft.
engine plant was built near the former 6.5L diesel engine plant, and many of the employees were
able to transfer to the new joint venture.
The totally new engine design was a 6.6L, 90-degree, direct-injection, overhead valve, fourvalve-per-cylinder, turbo-charged diesel V8 with aluminum high swirl cylinder heads. The
electrically controlled common-rail fuel system provided maximum power for each pulse of fuel
used and allowed full authority in injection timing and quantity. This combination along with
pilot injection provided operating quietness and smoothness typical of similarly sized gasoline
engines.
When it came time to decide upon the marketing name for the new B908 engine, GM was
already handicapped by its poor diesel reputation. The name itself was critical, as it would
compete against Ford’s established “Powerstroke” Diesel engine. Dodge was using the Cummins
engine and needed no other name, so after many meetings the engine was named Duramax
Diesel 6600. Like the joint venture name, “Duramax” was meant to highlight the durability and
reliability of the new engine.
In late 2000 the Duramax Diesel 6600 debuted in the new 2001 HD pickup trucks. Brought to
market in only 37 months, it was the fastest new engine developed by GM Powertrain – at that
time. The engine was an immediate success, making Ward’s Magazine “10 Best Engines” both
in 2001 and 2002, and bringing up GM’s market share from 3 percent to 30 percent in the HD
Diesel pick-up truck market.
So now that we know how it got here, let’s take a look at the basic specs of this engine, the RPO
designations and how the proliferation of the major engine components has taken place. In
addition, we’ll highlight some of what you need to know and watch out for as you go through the
remanufacturing of these engines.
Timeline:
2001 Duramax
The RPO LB7 (engine code “1”) was first introduced in 2001 and continued until 2004. This is a
32-valve design with high-pressure common-rail direct injection and aluminum cylinder heads.
The most problematic issue with the LB7 is injector failure. Since the injectors are under the
valve cover in the engine, lubricating oil fuel dilution occurred and often ended in a catastrophic
engine failure. A class action lawsuit against GM resulted in an extended warranty for this
situation for 7 year/200,000 mile coverage.
The following trucks use the LB7:
• Chevrolet Kodiak/GMC Topkick
• Chevrolet Silverado/GMC Sierra HD
Engine Specs:
• Engine type: 6,599 cc (6.599 L; 402.7 cu in) V8 turbo
• Bore x Stroke: 4.06˝ (103.1 mm) x 3.90˝ (99.1 mm)
• Block/Head: Cast gray iron/cast aluminum
• Aspiration: Turbocharged & Intercooled
• Valvetrain: OHV 4-V
• Compression: 17.5:1
• Injection: Direct; Bosch High Pressure Common-rail
• Power/Torque: 300 bhp (220 kW) @ 3100 rpm / 520 lb-ft (705 N·m) @ 1800 rpm.
2004 Duramax
The RPO LLY (internally called the 8GF1 – engine code “2”) debuted in mid-2004 and
continued until the end of 2005. The LLY was GM’s first attempt to implement emissions
requirements on its diesel trucks. To meet this goal GM turned to a newly developed Garrett
turbocharger with a variable geometry vane system and installed an Exhaust Gas Recirculation
valve. Learning from problems with injectors in the previous LB7, GM changed the valve covers
to not only remove them from the engine oiling system but allow access to the injectors without
having to remove the valve covers.
Early on, problems came forward from customers complaining of severe overheating, and, in
some situations, blown head gaskets. Although initially GM denied that it was a problem, after it
was sued by a consumer group it relented and included overheating and blown head gaskets as a
warranted item.
The following trucks used the LLY engine:
• 2006 Hummer H1 Alpha
• Chevrolet Silverado/GMC Sierra HD
Engine Spec changes:
• Power / Torque: 310 bhp (230 kW) @ 3000rpm / 590 lb·ft (800 N·m) @ 1600 rpm
• Head casting is c/n 8gf1
• Block casting is c/n 22351021213
2006 Duramax
RPO 2006 LLY (engine code “2”) debuted in the beginning of 2006 and ended production with
the start of the 2007 calendar year. While it retained the LLY designation, mechanically it is
identical to the LBZ and is mated to the new 6-speed Allison transmission.
RPO LBZ (engine code “D”) debuted in late 2006 and continued into 2007, sold only in the
“classic” body style. It has a more powerful tune loaded into the computer that allows it to
produce more power and torque.
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 length was 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.
LBZ applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• GMC TopKick
LLY applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• Chevy Express full-size (reduced power output mated to a 4l85E transmission)
• GMC Savanna full-size (reduced power output mated to a 4l85E transmission)
Engine Specification changes:
• Compression: 16.8:1
• Injection: Bosch High Pressure Common-rail
• For a chart explaining the Power/Torque relationships in this model year, see the enhanced
version online. Details at the end of this article.
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