Chevy Geek

Chevy repair advice, parts recommendations; troubleshooting, maintenance, specifications, performance tips, and picture gallery

LB7 Vs. LBZ Vs. LLY: Which Is The Best Duramax Engine?

The LBZ Duramax V-8 engine is more powerful than the LB7 and LLY with its 605 lb. ft torque at 1600 rpm and 310 bhp at 3000 rpm. LLY has two variants; one with a power output of 310 bhp at 3000 rpm and another 250 bhp at 3200 rpm. LB7 comes with a power output of 300 bhp at 3200 rpm.

LB7 model years range from 2001 to 2004 and LBZ from 2006 to 2007. The LLY had two production cycles; one was produced from 2004 to 2005 and another from 2006 to 2007. The three engines are part of DMAX’s joint venture that comprises General Motors and Isuzu.

They are part of the Duramax lineup with diesel-fueled V-8 and inline (I) engines. We will look at what makes each of them unique and how they stack up against each other.

LB7 vs. LLY vs LBZ: Similarities


You will notice that the LB7, LLY, and LBZ engines have the same displacement of 6.6 Liters. The engine design is the same for all three from 2001 to 2007 with very few modifications. The 403.9 cu in (6,619 cc) engine was enough to house the 32-valve design.


The three Duramax engines have the same layout that persisted in the DMAX lineup to date with the L5D that started production in 2019. The layout in these engines is the V-8 configuration that utilizes eight cylinders. The cylinders are divided into two banks and share a crankshaft in a V-shaped design layout.



All engines in the Duramax group use Diesel fuel, including the LB7, LLY, and LBZ. Diesel is among the most efficient fuels because of its higher energy when compared to gasoline. The use of diesel fuel sets Duramax engines ahead of most gasoline engines.


LB7, LLY, and LBZ utilize a similar turbocharged and intercooler aspiration system. The same combination of systems was applied to the group engines until 2021 with the L5D Duramax engine.

Block/Head Materials

The engine head in the LB7 LLY and LBZ is cast aluminum. On the other hand, the engine block is made of cast iron in the three variants. You will often notice the block material of the LB7 and LLY being mentioned as-cast gray iron.

Read more: Best Duramax Engine: Best Years And Worst Years

LB7 Vs. LBZ Differences

Generations, Years, VIN code

The LB7 is the first one with production years from 2001 and early 2004 when the LLY began production.

The standard coding system used to register the above engines is the RPO (Regular Production Option) from General Motors. The three alphanumeric characters of the codes denote the modification and specific variant of the engine. The LB7 is the first one with production years from 2001 and early 2004 when the LLY began production.

The production of LBZ Duramax engines was delayed due to some hindrances in getting EPA certifications. In the meantime, the company produced a variant of LLY engines with similar specifications as the predecessor but with less power output.

The manufacturing processes would fully kick in in 2006 and lasted till 2007. LBZ engines saw the first DMAX engines with computer tunes, making them one of the most reliable engines of the group.  

Power Output

The most powerful Duramax engine of the bunch is the LBZ which produces more power and torque at the least RPMs. It comes with a power output of 310 bhp at 3000 rpm.

The oldest of the two, the LB7, has a power output rating of 300 bhp at 3200 rpm

Torque Output

The two engines do not share the same torque output. LB7 is rated at 520 lb. ft. LBZ has the highest torque of 605 lb. ft at 1600 rpm.

Compression Ratio

The compression ratio never changed till the production of LBZ started. LB7 was designed to have a ratio of 17.5: 1 while LBZ comes at 16.8:1.


One of the reasons why experts rarely recommend LLY, LB7, and LBZ is because they were plagued with lots of issues. The most common problems with the LB7 included:

  • Bad fuel injectors.
  • The lack of fuel lift pumps.
  • Water pump leaks.
  • Overheating.
  • Head gasket failures.
  • Weal tie rods.
  • Leaking O-rings.

The second LLY and LBZ had fewer issues, including cracked pistons, glow plug failures, EGR problems, water pump issues, and Allison 1000 transmission line leaks.

Which Is Better?

LBZ Duramax engines are better than LB7 due to their massive computerization compared to the older machine. Moreover, LBZ engines have fewer mechanical issues that make their life span much more considerable than LB7 engines.  

A video about the LB7 engine.

Read more: TH350 vs. TH400 vs. 4L60E vs. 700R4

LLY vs. LBZ Differences

Generations, Years, VIN code

LLY debuted in mid-2004 in vehicles such as the Chevrolet Silverado and GMC Sierra HD of the same year.

LLY debuted in mid-2004 in vehicles such as the Chevrolet Silverado and GMC Sierra HD of the same year. Production of this unit would go on till the end of 2005. In 2006, the LBZ took over the Duramax lineup and lasted all the way to 2007.

Power Output

LLY engine from 2004 to 2005 has a power output of 310 bp at 3000 rpm but a smaller torque at the same rpms. The LLY variant from 2006 to 2007 comes with a smaller power rating of 250 bhp at 3200 rpm. LBZ has a similar power output to the first LLY variant.

Torque Output

LLY from 2004 to 2005 has a torque of 590 lb. ft at 1600, with its later version coming in at 460 lb. ft at 1600 rpm. LBZ sets itself apart in this regard with a much higher torque of 605 lb. ft at 1600 rpm.

Compression Ratio

LBZ is the only engine among the three with a different compression ratio (16.8:1). LLY has the same ratio as LB7 at 17.5:1.


The first LLY engine had similar issues with the LB7 engines, including turbo inlet manifold problems, glow plug failure, bent rods, head gasket failures, water pump failures, overheating injector harness chafing, and steering/suspension problems.

LBZ has fewer issues than LLY engines, with most tough issues being cracked pistons, EGR problems, and transmission leaks.

Which Is Better?

LBZ engines from 2006 to 2007 are the best compared to LLY of any year. This is primarily attributed to their fewer mechanical issues, making them more reliable.

A video about LLY vs LBZ Q&A.

LB7 vs. LLY Differences

Generations, Years, and VIN Code

LLY succeeded the LB7 Duramax engines in 2004 and completely took over the group in the middle of that year till 2006. LB7 only lasted for three years between 2001 and 2004.

Power Output

Generally, LLY engines are more powerful than the LB7, which has a smaller power output of 300 bhp at 3200 rpm. LLY from 2004 is rated 310 while the later version has a smaller output of 250 bhp.

Torque Output

The torque rating for LB7 is 520 lb. ft at 1600 rpm, while the LLY engine was first rated at 590 and later at 460 lb. ft at 1600 rpm.

Compression Ratio

The compression ratio for the earlier LLY and the LB7 is similar at 17.5:1. Later LLY, which is sometimes mistaken for the LBZ, comes with a 16.8:1 compression ratio.


According to the outlined comparison chart, you will notice that LLY and LB7 engines share a lot of issues in common that make them quite hard bargains.

Which Is Better?

LLY was the first Duramax engine to implement emissions requirements, and the fuel injectors were also improved.

A video about LB7, LBZ, LLY explained.

Read more: 4L60 Vs 4L60E Vs 4L80E Vs 4L80

LB7 vs. LLY vs. LBZ: Which Is The Best?

The LBZ Duramax engines are better than the LLY or the LB7. LBZ engines introduced many new features, such as fuel injectors that sprayed directly onto the glow plugs for faster and better-quality starts.  

The glow plugs were also improved to heat up quicker via an independent controller. This eliminated massive glow plug failures in the LLY and LBZ engines. Pick up the LBZ for your GMC or Chevy truck to get the best of pre-2007 V-8 diesel engines.

A video about LB7, LLY, and LBZ buyer guide.

Read more: LS vs. LT vs. LTZ: What Do They Mean On A Chevy?


  • Randy Worner

    My name is Randy Worner and I am the founder of I have been working on cars and trucks for almost 45 years. For the last 36 years I have taught Automotive / Diesel Technology classes for UTI, Snap On Tools, Chrysler, Pepboys, Lone Star College, NAPA and TBC Corporation. I also own a technical writing company known as Supreme Technical Services. It is ASE Gold Seal certified and Blue Seal Certified Author of auto/truck repair information.

Leave a Comment

Your email address will not be published. Required fields are marked *