August 12, 2020

What is So Special About the LBZ Duramax?

Written By: ProSource Diesel

History of the LBZ

About a decade ago, Chevy began offering the LB7 engine in a variety of its trucks.  From 2001 through mid-2004, the engine proved reliable and it sold well.  But in mid-2004, Chevy introduced the LLY engine and although it was also popular at the time, it had several performance issues including overheating.  To fix that and other problems, Chevy replaced the LLY with the Duramax LBZ which debuted in 2006 and continued to be manufactured through 2007.

How the Short-Lived LBZ Made Its Mark

The 6.6-liter Duramax LBZ was a short-lived engine. Only available for two model years due to increasingly strict emissions standards, the LBZ was a more aggressively tuned version of the previous LLY engine. Mechanically, the LBZ used the same Duramax parts as the LLY. However, the LBZ generated 360 horsepower over the LLY’s 310 horsepower. Torque increased as well, going from 605 pound-feet with the LLY to 650 with the LBZ.

The LBZ employed a thicker block casting, meatier connecting rods, and a higher pressure common-rail fuel system. This gave it more power and reliability versus any other Duramax to that point. Despite the LBZ’s short lifespan, it remains one of the most popular Duramax engines due to its power, dependability, and lack of strict emissions technology.

What Made the LBZ Special?

The LBZ was the first Duramax engine to be paired with the six-speed Allison 1000 automatic transmission. The new six-speed was capable of handling more power than the previous five-speed.

Perhaps the biggest claim to fame for the LBZ is that it was the last Duramax engine without the emissions control technology that would hamper the fuel economy and reduce the lifespan of diesel engines that followed. For these reasons and more, Chevy Silverado and GMC Sierra HD trucks with the LBZ engine continue to be in high demand, despite being over a decade out of production.

In addition to the engine not being held back by emissions control technology, stronger LBZ Duramax parts ultimately added to this engine’s performance and durability. A stronger block paved the way for more horsepower and torque vs. the LLY.

GM also improved the LBZ over the LLY by adding:

– More webbing in the LBZ’s main bearing regions

– Taller main bearing caps

– 4mm deeper bores for the main cap bolts

In order to make room for the deeper bolt holes, the oil feed holes were constructed 2mm smaller.

The LBZ also employed stronger rods. The steel-forged and cracked-cap design may have been the same as the LLY and LB7 rods, but they were meatier on the big end versus the other two engines. In performance terms, this means they were capable of handling about 100 more horsepower than the previous engines. The meatier rods brought more rotating mass, but it was still rare for the LBZ engine to experience bent rods.

New and improved fuel rails and injectors complemented the higher-pressure common-rail system, which helped increase the horsepower and torque over the LLY. The Bosch CP3 fuel pump was integral in creating the extra pressure.

A larger turbo inlet manifold was also employed in the LBZ versus the LLY. This addition removed the previous bottleneck from the turbocharger’s compressor side, which resulted in cooler temperatures for the intake and exhaust. The turbocharger also didn’t have to work as hard to create boost, which reduced lag.

LBZ Weak Links

The LB7 and LLY engines were known for rod weakness, but the LBZ had trouble with its cast-aluminum pistons. In higher-power applications, the pistons were very prone to cracking. LBZ Duramax upgrades with larger injectors and a larger turbo caused the majority of failures. The cracks almost always occurred on the centerline of the lower wrist pin. Symptoms of a cracked piston were very obvious with exhaust smoke and a bad misfire.

The LBZ stock turbo was known for occasional sticking due to the accumulation of corrosion and carbon. Energetic acceleration sometimes helped the turbo to unstick, but the best way to fix it was to remove the turbo and clean it.

Another issue came with the plastic impeller water pumps. They were prone to failure on higher mileage engines and sometimes caused overheating while cruising. Despite this, most of the water pumps still lasted between 150,000 and 200,000 miles.

LBZ Specs

  • Production Years – 2006, 2007
  • Design – 90-degree V8
  • Bore – 4.06 inches
  • Stroke 3.90 inches
  • Displacement – 6.6-liter (403 cubic inches)
  • Compression Ratio – 16:8:1
  • Block – Deep skirt, cast iron
  • Injection System – Bosch high-pressure common-rail direct injection
  • Intercooler – Air to air
  • Emissions – Exhaust gas recirculation, diesel oxidation catalyst
  • Horsepower – 360 at 3,200 RPM
  • Torque – 650 pound-feet at 1,600 RPM
  • Valvetrain – OHV, four valves per cylinder, single cam
  • The stock LBZ parts specs are as follows:
  • Rods – Forged steel, fractured cap
  • Pistons – Cast-aluminum
  • Heads – Cast aluminum with six 14mm diameter bolts per cylinder
  • Turbocharger – Garrett GT3788VA VVT
  • Injection Pump – Bosch CP3
  • Injectors – Bosch solenoid

Final Words

Although the LBZ engine had a few weak links, overall it improved greatly on previous Duramax engines. It corrected previous issues with the LLY and LB7 engine and did not employ heavily restrictive emissions technology that often killed power and reliability in future engines.

Whichever Duramax engine you use, you can count on ProSource Diesel for all your Duramax performance parts and Duramax diesel parts needs. ProSource is where repair shops shop for reliable and hard to find parts and kits.

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