Over 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. In mid-2004, Chevy introduced the LLY engine. 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.
The 6.6-liter Duramax LBZ was a short-lived engine only available for two model years. To meet 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, but the LBZ generated 360 horsepower, while the LLY only generated 310 horsepower. Torque increased as well, going from 605 pound-feet with the LLY to 650 with the LBZ.
The LBZ employed a thicker engine 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.
The LBZ is significant because it 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 transmission.
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 out of production for over a decade.
In addition to the engine’s performance not being held back by emissions control technology, the stronger LBZ Duramax parts improved this engine’s performance and durability. A more powerful block paved the way for more horsepower and torque vs. the LLY.
GM added many other improvements to the LBZ over the LLY, including more webbing in the LBZ’s main bearing regions, taller main bearing caps, and 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 was the same as the LLY and LB7 rods, but they were meatier on the big end versus the other two engines. This made them capable of handling roughly 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.
The LB7 and LLY engines had rod weakness, but the LBZ had trouble with its cast-aluminum pistons. The pistons were very prone to cracking in higher-power applications. The majority of failures were caused by LBZ Duramax upgrades with larger injectors and a larger turbo. 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 water pumps still lasted between 150,000 and 200,000 miles.
The stock LBZ parts specs are as follows:
Although it had a few weak links, the LBZ engine was overall a great improvement upon 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.
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