Family Lineage – The Evolution Of GM Diesel Truck Engines

General Motors has had an interesting history when it comes to diesel engines. We thought it would be a good idea to document the history of GM’s continuous light duty diesel engine offerings in the truck market.

6.2L Engine Specs

  • Bore: 3.98 in.
  • Stroke: 3.80 in.
  • Displacement: 379 Cubic inch (6.2L)
  • Injection: Mechanical; Indirect Injection
  • Turbo: N/A
  • Base Horsepower: 130 to 140 hp at 3,600 RPM
  • Base Torque: 240 to 255 lb-ft at 2,000 RPM
  • Emissions: None
1982 – 1993

Introduced at the same time as Ford’s 6.9L, GM’s 6.2L was the first permanent diesel offering in a consumer light duty truck for Chevrolet and GMC. Learning from the 5.7L diesel GM produced for the car market, they opted to partner with a diesel engine manufacture for their trucks. So, GM partnered with Detroit Diesel to build their new diesel engines for their truck line. The 6.2L wasn’t designed as a power house, but was a solid attempt at building a reliable diesel that was a good, fuel efficient alternative to the gasoline engines offered at the time. This was during the energy crisis, where fuel prices were sky high for that time.

The new 6.2L was able to produce 130 horsepower and 240 lb-ft of torque while achieving high teens to low 20’s mpg. The fuel was delivered by a Stanadyne DB2 rotary injection pump and the injectors; injected fuel into a pre-combustion chamber. The compression ratio was 21.5 to 1, mostly thanks to it being natural aspirated.

GM_Family_62

6.5L Naturally Aspirated Engine Specs

  • Bore: 4.06 in.
  • Stroke: 3.82 in.
  • Displacement: 397 Cubic inch (6.5L)
  • Injection: Mechanical; Indirect Injection
  • Turbo: N/A
  • Base Horsepower: 155 hp at 3,600 RPM
  • Base Torque: 275 lb-ft at 1,700 RPM
  • Emissions: None
1994 – 1995

In 1992, GM introduced new body styles for both GMC and Chevrolet pickup. Instead of discontinuing their old body styles, they rebadged them as HD’s. The HD (Heavy Duty) trucks continued to run the naturally aspirated engine until they were discontinued in 1995.

The new body style trucks ran a turbocharged 6.5L (see below) and in 1994, GM increased the displacement of the naturally aspirated 6.2L to 6.5L. This allowed them to share more components which reduced manufacturing cost. The increased displacement, also, increased the horsepower and the torque.

6.5L Turbocharged Engine Specs

  • Bore: 4.06 in.
  • Stroke: 3.82 in.
  • Displacement: 397 Cubic inch (6.5L)
  • Injection: Mechanical; Indirect Injection
  • Turbo: Single Turbocharger
  • Base Horsepower ’92: 180 hp at 3,500 RPM
  • Base Torque ’92: 380 lb-ft at 1,700 RPM
  • Base Horsepower ’93: 190 hp at 3,400 RPM
  • Base Torque ’93: 380 lb-ft at 1,700 RPM
  • Emissions: None
1992 – 1993

As mentioned above, in 1992 GM split their diesel engine offerings. They had the 6.2L for their HD line of trucks and a new larger displacement, turbocharged engine (still produced by Detroit Diesel) was put into their regular lineup.

Initially, the 6.5L used the same basic engine architecture but the internals were strengthened up, piston oil squirters were added and the piston had additional surface coatings to improve durability.

A Stanadyne DB2 rotary injection pump was still used for these engines even though the displacement was increased as well as boost added. To gain the increased displacement, the bore was increased to 4.06 (from 3.98) inches and the stroke was altered to 3.82 (up from 3.80) inches. The combination of the increased displacement and the addition of boost, resulted in a rather large horsepower increase compared to their 6.2L counterpart. They were able to bump the power up to 190 horsepower (up from 140) and their torque rating increased from 255 lb-ft to 380 lb-ft.

GM_Family_65

6.5L Turbocharged Engine Specs

  • Bore: 4.06 in.
  • Stroke: 3.82 in.
  • Displacement: 397 Cubic inch (6.5L)
  • Injection: Mechanical; Indirect Injection
  • Turbo: Single Turbocharger
  • Base Horsepower: 180 to 215 hp up to 3,400 RPM
  • Base Torque: 360-430 lb-ft up 1,800 RPM
  • Emissions: None
1994 – 2000

With government regulation mandating all vehicles be OBDII (On Board Diagnostics) capable by 1996, GM added electronics to their 6.5L. GM didn’t convert the entire engine over to be electronically controlled. Instead, they added electronic regulation to their injection pump.

The injection pump was switched from the Stanadyne DB2 rotary injection pump over to Stanadyne’s DS4 rotary injection pump. This pump was still mechanical, but it was electronically regulated. For the day, these pumps were a good step forward but the engines remained pretty much a mechanical engine up until their replacement in 2001.

LB7

6.6L LB7 Duramax Engine Specs

  • Bore: 4.06 in.
  • Stroke: 3.90 in.
  • Displacement: 403 Cubic inch (6.6L)
  • Injection: Direct Injection Common Rail
  • Turbo: Single Turbocharger intercooled
  • Base Horsepower: 235 hp at 2,700 RPM; 300 hp at 3,100 RPM (2004)
  • Base Torque: 500 lb-ft at 1,600 RPM; 520 lb-ft at 1,800 RPM (2004)
  • Emissions: EGR, DOC (CARB engines only)
2001 – 2004 (LB7)

In 2001, Chevy decided to raise the bar and set a new standard for all others to judge themselves against. This was beginning of a new era, the Duramax! Stepping away from Detroit Diesel and entering a partnership with Isuzu, GM and Isuzu teamed up to design a totally new engine. This engine was designed to answer the horsepower and torque needs of current and future drivers, meet emission standards, and reliability. With Ford and Dodge offering high horsepower/torque diesels, the 6.5L just wasn’t able to remotely compete. Little did they realize, that a decade plus later they would still be in the fight while the other two companies have redesigned their engines.

Initially, a risky proposition using aluminum cylinder heads given the decades of failures by other manufacturers, Isuzu went ahead with production with an aluminum cylinder head. There were some early issues (nothing like the Ford 6.0’s) but they were able to find the right recipe for the Duramax cylinder heads rather quickly and none of the future Duramax engines exhibited an issue. The heads are designed as a 4 valve per cylinder head (one rocker per 2 valves). The high-pressure common rail fuel pressure is fed by a Bosch CP3 pump feeding a direct injection injector.

The rest of the engine was built to pretty standard diesel specs. The rods, mains, and crank are all built pretty heavy and beefy. The engine is an eight-cylinder V design with the gear train in the front of the engine.

LLY

6.6L LLY Duramax Engine Specs

  • Bore: 4.06 in.
  • Stroke: 3.90 in.
  • Displacement: 403 Cubic inch (6.6L)
  • Injection: Direct Injection Common Rail
  • Turbo: Single Variable Geometry Turbocharger intercooled
  • Base Horsepower: 310 hp at 3,000 RPM
  • Base Torque: 520 lb-ft at 1,600 RPM (’04 – ’05); 605 lb-ft at 1,600 RPM (’06)
  • Emissions: EGR, DOC (CARB engines only)
2004 – 2006 (LLY)

The next few generations of the Duramax are upgrades to the solid design. Most companies would have made these running changes, but GM identified each revision as a different model. The next revision, referred to as the LLY was a mid-year change in 2004. The easiest way to tell whether the engine is a LB7 or an LLY is by the valve covers. The LLY has redesigned valve covers, that allow the injectors to be removed without removing the valve covers like the LB7. With the introduction of the LLY, emissions equipment started to show up. The LLY’s have: EGR systems to reduce emissions, a new higher pressure fuel injection system (23,000 psi up from 21,000 psi) and a variable geometry turbocharger was added.

LBZ

6.6 LBZ Duramax Engine Specs.

  • Bore: 4.06 in.
  • Stroke: 3.90 in.
  • Displacement: 403 Cubic inch (6.6L)
  • Injection: Direct Injection Common Rail
  • Turbo: Single Variable Geometry Turbocharger intercooled
  • Base Horsepower: 360 hp at 3,200 RPM
  • Base Torque: 650 lb-ft at 1,600 RPM
  • Emissions: EGR, DOC (CARB engines only)
2006 – 2007 (LBZ)

As the horsepower wars heated up between the big three, GM answered. The LBZ featured more boost pressure, more rail pressure (26,000 psi) and a lower compression ratio (16.8:1). The injectors were, also, upgraded to a PEZO injector offering better response and tuning ability to help reduce emissions further (the number of holes in the injector tip increased from 6 to 7 as well). To better utilize the PEZO injectors, the ECM was, also, upgraded to a more powerful E35 ECM. With the additional air and fuel being available, there were some minor lower-end changes and the horsepower increased up to 360 horsepower up from 310 while the torque rating was bumped another 45 lb-ft.

LMM

6.6 LMM Duramax Engine Specs.

  • Bore: 4.06 in.
  • Stroke: 3.90 in.
  • Displacement: 403 Cubic inch (6.6L)
  • Injection: Direct Injection Common Rail
  • Turbo: Single Variable Geometry Turbocharger intercooled
  • Base Horsepower: 365 hp at 3,100 RPM
  • Base Torque: 660 lb-ft at 1,800 RPM
  • Emissions: EGR, DPF, DOC
2007 – 2010 (LMM)

The LMM engines remain structurally the same as previous generations of the Duramax engine family. This generation of engines faced the toughest emissions changes of any previous generation.

As a result, the LMM’s are the first engine to feature a Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC) as standard 50 state emissions equipment.

In addition to the fore mentioned emissions equipment, the EGR cooler was increased and a throttle valve was added to the intake to help flow more EGR at low rpm/load conditions.

LML

6.6 LML Duramax Engine Specs.

  • Bore: 4.06 in.
  • Stroke: 3.90 in.
  • Displacement: 403 Cubic inch (6.6L)
  • Injection: Direct Injection Common Rail
  • Turbo: Single Variable Geometry Turbocharger intercooled
  • Base Horsepower: 397 hp at 3,000 RPM
  • Base Torque: 765 lb-ft at 1,600 RPM
  • Emissions: EGR, DPF, DOC
2011 – present (LML)

With the horsepower and torque wars reaching a climax, the Duramax has and will continue to answer the call from its competitors. While the Duramax doesn’t always stand on the top of the hill, it has repeatedly been able to keep up with its competitors without a complete redesign. The LML engine series faced even tougher emissions and with some of the internal components being redesigned (like the pistons featuring a larger compression chamber to drop the compression down to 16:1) is able to meet them while increasing horsepower and torque output.

*Acronyms: 

  • EGR: Exhaust Gas Recirculation
  • DOC: Diesel Oxidation Catalyst
  • DPF: Diesel particulate filter

Article Sources

About the author

Chad Westfall

With diesel running through his veins from childhood, Chad has more than a decade of experience in the automotive industry. From editorial work to wrenching, there isn’t much he hasn't conquered head-on. When he’s not writing and shooting trucks and tech, you’ll find him in the shop working on turning the ideas floating around in his head into reality.
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