Since 2001 when the LB7 Duramax first hit the market, the Duramax name itself has been synonymous with the 6.6L V8 diesel engine. Even throughout the years and changes, the Duramax name simply referred to the 6.6L, as there were no other Duramax engines, but that all changed in 2016 when the 2.8L four-cylinder LWN Duramax landed here in the US, which was followed up in 2019 with the 3.0L six-cylinder LM2 Duramax.
Why is GM Offering These Engines?
So getting into this, let’s look at where each engine came from because, ironically, neither of them is completely a GM product. In terms of the 2.8L engine, it’s actually an older engine from VM Motori, which is an engine design and manufacturing company now owned by Fiat.
This specific engine is actually the A 428 dual-overhead-cam, which is an evolution of the R 428 dual-overhead-cam. So, it’s not like the 2.8L Duramax was a freshly designed engine. Its roots of it can be traced back to 2001 or even earlier than that, depending on how deep you go.
And that’s not a particularly bad thing, as VM Motori is a pretty big company with a handful of decent under their belt, including the 3.0L EcoDiesel you’ll find in the Ram.
For the 3.0L LM2 Duramax, it was designed as a collaboration between Opel and GM, as they were in business together up until 2017, and as such, the architecture and base design of the 3.0L Duramax is based on two smaller Opel engines but simply scaled up and modified to become an inline-six engine.
“It is a clean-sheet design from the air intake down to the engine mounts. Very, very few common things were used from the other Duramax. We’ve optimized everything in this engine’s design to fit into the new-generation Silverados while incorporating advanced combustion and emissions technologies to optimize performance and efficiency.”
– John Barta, assistant chief engineer for the 3.0L Duramax.
And I’ve mentioned this in other videos, but it’s worth reiterating here before we move on, which is that these engines are not meant for the same level of work as the 6.6L Duramax, and it’s not even close. These engines are offered in GM’s half-ton and smaller trucks for those who want a diesel engine without having to drive a 3/4 ton truck as a daily driver.
While the 3/4 ton Duramax-powered trucks are great at towing, hauling, and getting work done, they’re more expensive to buy, quite a bit larger in size, harder to drive, harder to park, and so on. A lot of people flat out don’t want to daily drive a 3/4 ton truck but still want a diesel engine, which is exactly where the 2.8L and 3.0L come into play, as well as the competitors like the 3.0L EcoDiesel, 3.0L Powerstroke, and so on.
Now taking a deeper look, let’s look at the cylinder heads of both engines, starting with the smaller 2.8L cylinder head. This is a cast aluminum head with dual overhead cams, four valves per cylinder, and a finger-follower actuation system. The US version of the head supposedly had enlarged exhaust ports, larger passages, and other modifications.
For the 3.0L Duramax, we also have a cast aluminum cylinder head, dual overhead cams, and four valves per cylinder. On paper, these engines are pretty similar in terms of the design of the head, which kind of makes sense as there’s not really any reason to run something cam-in-block type of design in this type of application.
And it’s worth noting that both heads are constructed from cast aluminum for both the thermal benefits and weight savings. In applications where the base power level is much higher than these engines, cast iron can be the better choice, but considering how low the power output of these engines is, aluminum is more than strong enough.
Where things differ greatly with these engines is with the timing system, which is what drives the camshafts and times the camshafts to the rotation of the crankshaft. For larger commercial-style diesel engines, we generally see a gear-driven system, which is very low maintenance and extremely strong, but both of these engines are void of a gear-driven instead.
Instead, on the 2.8L Duramax, we have a timing belt with a 150,000-mile interval for replacement. Presumably, they avoided a timing gear system to save cost but also to reduce total noise, vibration, and harshness.
On the 3.0L Duramax, things are significantly worse with a timing chain system, but that’s not the issue. The issue is the fact that the whole timing system is on the back of the engine rather than the front. Meaning if anything happens with it or it needs maintenance, your transmission has to come off in order to access anything.
You might be wondering why GM would do this, considering all the downsides, and it’s all centered around packaging. Ultimately they needed to keep this engine as short as possible for improved packaging in their trucks, and this is supposedly one of the solutions they used to shorten the engine.
Block and Internals
Moving down, we can take a look at the cylinder block and internals of each engine. Again, starting with the 2.8L Duramax first, we have a grey cast iron cylinder block, which is relatively standard in the world of diesel engines. However, with any modern four-cylinder engine, we almost always see cast aluminum instead of iron for weight savings and thermal efficiency.
This is in stark contrast to the larger 3.0L Duramax, which does use a cast aluminum block. It’s kind of strange to see these two using different materials for their engine blocks, especially considering how low the power output for the engine is, as aluminum would’ve likely been strong enough for both.
This is just speculation on my part, but in all likelihood, the reason for the 2.8L Duramax using an iron block is simply because it was designed by VM Motori quite a while ago, and they just simply didn’t see the need to redesign the block for a superior material. Basically, GM is being lazy and figured iron would be fine for the 2.8L, and to be fair, it is. There’s nothing wrong with the iron block. It’s just heavier and less thermally friendly than an aluminum equivalent.
Something worth noting is that on the 3.0L Duramax block, GM is using iron cylinder liners for improved long-term durability and the block itself features a deep skirt design for further improved rigidity and block stiffness.
All that means is that as far as the block and internals, neither the 2.8L nor 3.0L is particularly special, strong, or interesting. They’re simply basic designs that get the job for the given application. If the application required more power, it wouldn’t be surprising for GM to switch these to a CGI block like the L5P Duramax, but it’s that’s just a hypothetical situation and speculation on my part.
In terms of the injection system, both engines are using systems supplied by Denso. The 2.8L Duramax is a common rail injection system that peaks out at 29,000psi with solenoid-type injectors.
The LM2 uses common rail injection system peaks out at 36,250 psi, which is one of the factors that allows the LM2 to generate as much power as it does. This injection system features nine-hole nozzles that can fire up ten times per combustion cycle, which simply means more consistent and stable combustion performance, ultimately meaning a smooth, quieter, and better-performing engine.
It’s very interesting that the 2.8L uses solenoid-type injectors, as piezo-injectors are typically found in modern diesel engines, but with modern innovation, clearly, Denso was able to supply GM, and VM Motori with an injector that was good enough to meet the power, emissions, and fuel efficiency demands.
Intake and Turbo
That takes us to the turbocharger, where both engines feature variable geometry turbochargers. For the 2.8L, the turbocharger comes from Honeywell, and for the 3.0L, the turbo comes from Garrett.
For those who don’t know, let me give a quick explanation of what a variable geometry turbo is. The size of the turbocharger has a big impact on power output and, more specifically, where the power is made. Big turbos make the most power at high RPM, and small turbos make the most power at low RPM.
The idea of a variable geometry turbocharger is to have both a small and large turbocharger packed into one unit. This works by using movable vanes to effectively change the size of the turbo, which has a big impact on how quickly it spools up and how much boost pressure it can produce at certain RPMs.
A big difference to note between these two engines intake systems, is that the 3.0L Duramax uses a variable intake manifold, which is simply a dual-pathway system with electronically controlled flaps for each cylinder. This allows the intake to have a long pathway and a short pathway.
The length, shape, and size of the intake runners has a big impact on power output and how efficiently the air enters the cylinder at any given RPM, which basically means it’s one more tool the 3.0L Duramax has for improved power output across the entire rev-range.
And that takes us to everyone’s least favorite part of any diesel engine, and that’s all the terrible emissions components that absolutely ruin reliability and make these engines much more expensive to run in the long term. Shoutout to the EPA for that one.
And to make this short, both the 2.8L Duramax and 3.0L Duramax have every single emissions component you’d expect on a modern diesel engine, including a diesel oxidation catalyst, diesel particulate filter, selective catalyst reduction, and exhaust gas recirculation.
And as a quick rundown on these systems and what they do, the EGR system basically just diverts some of the engine exhaust gas and routes it back into the intake, which ultimately lowers combustion temperature.
The diesel particulate filter captures excessive exhaust soot and burns it off through a regeneration mode, and the selective catalyst reduction uses diesel exhaust fluid to reduce tailpipe emissions output, at least in theory.
I would like to note, however, that the 3.0L Duramax uses a more efficient low-pressure EGR system as compared to the standard high-pressure EGR system. This was simply done in the name of improved efficiency, as it still has the potential weak points that plague nearly all diesel EGR systems.
It’s a little too soon to know how these emissions will fair in the long term, but looking at other examples, I’m pretty confident these systems will become reliability issues down the line.
Other important changes to note between the two engines include the 2.8L’s lack of a real truck transmission behind it. Unfortunately, GM is using the 6L50, which is the same transmission you’ll find in the V6 Camaro, a bunch of Cadillac applications, and so on.
It’s upgraded compared to the car-specific 6L50 for improved performance with towing and hauling, but it’s still lackluster compared to a true truck transmission such as the 6L80 and so on.
On the 3.0L Duramax, we have a unique oiling system that features a variable pressure pump for decreased drag on the engine and, ultimately, more efficiency. That, paired with the active thermal management system, makes the 3.0L Duramax quite efficient.
So, that’s a quick overview of the 2.8L versus the 3.0L Duramax. Neither engine are fully from GM, with the 2.8L coming almost entirely from VM Motori, which is now owned by Fiat, and the 3.0L coming as a collaboration between Opel and GM.
As far as which one is better. It’s really going to come down to what you plan on doing with the engine. Quite frankly, both of them have some design flaws. But, that being said, in terms of engine efficiency and innovation, the 3.0L Duramax is miles ahead of the 2.8L Duramax.
Both engines aren’t really meant for heavy work like the 6.6L Duramax, and as such, things like thermal efficiency, innovation, and more, are probably slightly more important, so I think it’s fair to crown the 3.0L Duramax as the superior engine in that regard.