LBZ engines are the oldest ones in LBZ vs. LMM vs. LML vs. L5P. LMM follows them, then LML, and the latest one, the L5P, from 2017 to the present.
L5P engines are also the best in power output and reliability, with the LBZ being the less powerful group.
The four engines are part of the Duramax engine lineup made under a joint venture between Isuzu and General Motors.
The joint venture was named DMAX, and it gave rise to a list of powerful diesel truck and SUV engines starting from 2001 to the present.
We will look at the similarities and differences between these engines made from 2006 to 2021.
We aim to show you their unique features and improvement throughout the years to help you pick your best choice.
LBZ vs LMM vs LML vs L5P: Comparison Chart
LBZ vs LMM vs LML vs L5P: Similarities
The Duramax engines came with a standard design and layout before the 2011 versions, the XLD25 engines.
All the engines from the LB7, LLY, LBZ, LMM, LML, LGH, L5P, and L5D share the same displacement.
The company opted for a 6.6 liter/402.7 ci engine design that went well with the layout.
Similar to the displacement. The LB7, LLY, LBZ, LMM, LML, LGH, L5P, and L5D Duramax engines are the same layout.
The design 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 lineup use Diesel fuel, including the LBZ, LMM, LML, and L5P.
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.
LBZ, LMM, LML, and L5P utilize a similar turbocharged and intercooler aspiration system.
The same combination of systems was applied to the group engines until 2021.
The engine head in the LBZ, LMM, LML, and L5P 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 LBZ and LMM being mentioned as-cast gray iron.
LBZ vs. LMM vs. LML vs. L5P Differences
Generations, Years, VIN code
The oldest Duramax engines are the LBZ.
They were produced after the production of LLY Duramax engines ended in the middle of 2006.
The production was delayed due to some issues with obtaining EPA certifications.
They featured a classic body style and enhanced engine computer tunes that set them apart from any previous generation of DMAX-produced engines.
LBZ engine continued production till 2007 and was the Duramax lineup to be put in Chevrolet Express and the Chevrolet Savanna in 2007.
Some of the improvements to the engine include upgraded bearing material, increased fuel injection pressure, a higher-pressure pump, improved machining and casting of the cylinder block, and a retuned air induction system.
The first application of the 32-bit E35 controller was in vehicles like the GMC Sierra HD and the GMC Topkick from 2006 to 2007.
The LMM did not replace LBZ engines. Instead, the LMM Duramax engines were built alongside LBZ halfway through 2007.
Their production continued for years till 2010.
The two engines share many common characteristics, including the compression ratio, the power output, and the injection system that includes the Bosch High-Pressure Common rail that came with CP3.3 injection pumps.
LML Duramax engines came later on in 2011 to improve upon the emissions of the LMM engines.
Its production lasted until 2016 and brought about changes that improved temperature control by redesigning the piston oil flow.
L5P engines took over in 2017 and are still being produced to date.
They are the latest model in the Duramax group, bringing customers the highest power output GM truck engines have ever made.
The power output is more significant in the latest engines, which are the L5P Duramax engines.
This is a huge leap of over 150 hp from the oldest engines, the LBZ and LMM.
The cast-iron block and cast aluminum head engines are still powerful machines despite their power output due to the tweaks and boost brought up by DMAX.
You can opt for the latest L5P if you want the extra power, but the LML middle child may serve you well with its power output of 397 hp/294 kW at 3000 RPM.
For a more reserved power rating, look at the LBZ and LMM, which share a similar wattage.
These diesel engines were fitted with internals capable of outputting 250 hp minimum at 3200 RPM and a maximum output of 360 hp at the same RPMs.
LBZ Duramax engines can produce 605 lb. ft / 820 Nm at 1600 RPM.
The redline is at 3200 RPM.
The torque was topped in the succeeding LMM engines but with varying degrees since LMM engines had various versions that produced different power outputs.
LMM engines from 2007 to 2010 in the Chevrolet Silverado HD and GMC Sierra HD produced 660 lb. ft torque at 1600 RPM.
The torque decreased to 630 lb. ft in the Chevy Kodiak LYE option and the GMC Topkick Medium duty.
It then decreased further to 520 lb. ft in the Chevy Kodiak LRX and GMC Topkick LRX options.
LMM Engines in the Chevrolet Express and GMC Savana produced a torque of 460 lb. ft at 1600 RPM.
The torque increased to 525 lb. ft in these vehicles’ 2011-2016 versions.
LML Engines from 2011 to 2016 produce 765 lb. ft at 1600 RPM.
The recent L5P is more powerful in terms of torque, producing a higher torque of 910 lb. ft at 1600 RPM in the Silverado HD and Sierra HD.
LBZ and LMM Duramax engines share the same compression ratio as the LML and L5P engines.
Despite the differences between the pairs, they all share similar bores and strokes that facilitate the production of comparable output.
LBZ from 2006 to 2007 comes with a bore and stroke of 4.06 x 3.90 inches, similar to the LML, LMM, and L5P.
These 6.6 Liter engines were made from a similar blueprint of the Duramax V-8 Engines.
LBZ and LMM have a compression ratio of 16.8:1, which enhances the 250-360 hp production at 3200 RPM for the two engines.
These engines were placed in the Chevrolet Kodiak, Chevrolet Silverado HD, Chevrolet Express, GMC Topkick, GMC Sierra, and GMC Savanna of their respective years of production.
LML and L5P engines, on the other hand, feature a compression ratio of 16.0: 1.
This enhances the production of the 397 hp on the LML and 445 hp on the L5P.
The L5P and LML engine applications were in the Chevrolet Silverado HD and GMC Sierra HD of their respective years of production.
L5P Duramax engines are the less plagued when it comes to the most common issues that these four engines experienced.
On the other hand, the LMM and LBZ engines have so many problems that make them a worse purchase among the four.
The most prevalent issues with the L5P engines included Manifolds Absolute Pressure sensor (MAP) failures, the Allison 1000 transmission issues, and an abnormal condition with the fuel injector number 4, which seemed to fail on most vehicles.
Apart from that, the L5P is an all-around average performer with minimal compilations.
LML engines from 2011 to 2016 came with a few common problems that include the Diesel Exhaust Fluid (DEF) heater failures and the DEF pump malfunctions.
These two issues affect the emissions of the engine.
DEF systems work by breaking down dangerous NOx emissions into less harmful products, including water and nitrogen.
Therefore, the LML engines also had NOx sensor failures and CP4.2 injection pump malfunctions.
LMM engines have leaking transmission lines, fuel pressure issues, crankshaft failures, transmission limitations, and DPF system issues.
LBZ’s most common problems include cracked pistons, water pump failures, Allison 1000 transmission line leaks, EGR problems, and Glow Plug failures.
LBZ vs. LMM vs. LML vs. L5P: Which Is The Best?
LBZ Vs. LMM
LMM engines are better than LBZ Duramax engines due to their broader application in more vehicles.
Moreover, LMM Engines have varying torque output ratings and power ratings that are more accommodating than those of the LBZ.
Besides that, the two engines have more similar qualities than differences starting with the compression ratio, build quality, and reliability.
LML Vs. LBZ
LML engines are better than LBZ Duramax engines by far because of more improvements on components like the design of the piston airflow.
Other improvements were made to the LML to ensure it was more emissions friendly.
LBZ is less conducive, thereby a worse option for the LML.
LMM Vs. LML
LML Duramax engines improved on the LMM engine.
Some of the changes included the enhanced exhaust emissions system, which complied with the new federal emissions laws for diesel engines.
This ensured noise reduction as well as improved engine rigidity.
LML Vs L5P
L5P engines are better than LML Duramax engines because of various factors like power output and the number of problems.
L5P experiences fewer issues, including MAP sensor failures, transmission, and fuel injector issues.
LML, on the other hand, comes with lots of problems that include DEF heater problems, NOx sensor failures, and DEF pump malfunctions.
Which Is The Best Overall?
L5P engines are the best overall between the LBZ, LMM, LML, and L5P engines.
They are more reliable and sustainable due to the few issues they are prevalent to and more powerful output.
You will get more out of the L5P since it is the latest version of the group engines with readily available spare parts and more life.