555 Horsepower. 1230 lb-ft of torque. 8.3 liters of turbodiesel glory. The new Chevrolet Silverado HD may share its body with the 2026 truck, but this mid-cycle update is a big deal: It brings with it the Mongoose, the biggest diesel engine ever offered in a heavy duty pickup, and one that can tow an outrageous 38,000 pounds. Here’s what it was like to drive.
If there’s one thing that heavy duty pickup truck brands enjoy, it’s oneupmanship. If you look at the last 15 years of torque figures, it’s really been Ford and Ram duking it out. In 2011, the Ford Super Duty’s 6.7-liter Power Stroke was the first HD truck to hit 800 lb-ft of torque — a monumental figure at the time. Ram caught up in 2013 with its 6.7-liter Cummins, while Chevy’s 6.6-liter “LML” Duramax hung out at 765 lb-ft all the way until 2017.
Chevy released the 910 lb-ft L5P Duramax in response, though by then, Ram’s Cummins had jumped to 850 lb-ft, 865 lb-ft, and then 900 lb-ft — just 10 lb-ft short of Chevy. Ford had countered Ram’s 850 lb-ft with a new 860 rating, and then when the Ram jumped to 900 lb-ft and Chevy jumped to 910 lb-ft, Ford went up to 925 lb-ft. So in 2017, Chevy was now no longer dead last; it was second.
But that didn’t last long, because the following year the Ram’s Cummins’ output elevated to 930 lb-ft. That same year, Ford’s Powerstroke’s output went to 935 lb-ft. In 2019 the Ram made 1000 lb-ft; in 2020, Ford’s truck made 1050 lb-ft; and then in 2021, the Ram started making 1,075. All the while, Chevy stayed at 910 lb-ft.
The Bowtie’s L5P got an update in 2024 to bring torque up to 975 lb-ft, but that was still short of Ram’s 1,075, and it was in this year that Ford’s figure jumped all the way up to 1,200 lb-ft.
This is all to say that Chevy has been in third place in torque every year for the past 15 years, except 2017. Which is why 2027 is such a huge deal: Chevy decided to go nuclear.
[Full Disclosure: Chevy flew me to Tucson, Arizona, and fed me lots of steak. It is the diesel of human food, and afterwards I could feel the torque coursing through my veins; I snapped a 1/2-inch bolt using only my fingers. -DT].
A Close Look At The 8.3-Liter Mongoose V8 Diesel
I’m feeling sick tonight, so this won’t be one of my patented 4,000 word deep-dive reviews, but let’s see what I can get cranked out before I pass out.
As I mentioned earlier, the current L5P has been around since 2017, receiving an update in 2024. In reality, that engine’s architecture can be traced all the way back 2001. “We’d stretched that architecture as far as it could go,” Rob Moran, the Assistant Chief Engineer for the heavy duty diesel, told me at the press event in Arizona. It was about four of five years ago that Chevy began planning to bring out the biggest diesel engine ever offered in the heavy duty segment.
Though the engine shares some basic traits with the outgoing V8 — it’s a 90-degree V8, it has aluminum cylinder heads, those heads contain four valves per cylinder, there’s a variable geometry turbo in the valley, etc. — there’s quite a bit new here. For one, the block, Chevy says, is made of a new compacted graphite iron versus the outgoing gray iron. Per Moran, gray iron is the entry point for strength, nodular iron is the strongest (but harder to machine), and compacted graphite iron offers 40-50 percent more strength than gray iron and is more machinable than nodular iron.
I dug into this a bit, learning the following from the Michigan-based Metal Casting Institute, a website that “provides casting information, educational material, training outlines and linkage to technical resources.” From MCI:
Gray cast iron is the simplest, most common and lowest cost form of cast iron in the world. The iron microstructure is characterized by the “Flake Graphite” qualities in the forms of: a.) Type, b.) Size and c.) Martrix.
Gray cast iron has excellent castability and machinability qualities, making it a high value for parts that can be heavy. In addition, gray iron has superior damping and thermal heat transfer, making it excellent for automotive brake systems. While it is strong, it is also brittle.
Compacted Graphite Iron (CGI)is a recent addition to the family of cast irons. As shown by the image to the right, the graphite is characterized as a “vermicular” or worm-like structure. This graphite structure produces an iron with most of the properties being in-between the Gray Iron and Ductile Iron families of properties. Simply stated, CGI has nearly the same castability and wear resistance characteristics as gray iron, but with improved strength. Being able to use CGI for engine cylinder blocks allows thinner wall sections and lighter weight.
MCI goes into detail, discussing the significant advantages MCI has over gray iron, particular in engine applications:
While not quite as strong as ductile iron [which is the same as nodular iron], compared to gray iron properties, CGI is 75 percent stronger and up to 75 percent stiffer. It is also twice as resistant to metal fatigue as gray iron. However, significantly important for use in engine cylinder blocks, the graphite morphology of CGI was [determined] to have similar friction and wear resistance characteristics as found in gray iron.
Engine Applications
With all of the material properties taken into consideration, engine designers found CGI ideally suited for engine cylinder block manufacturing, where lighter and stronger materials are needed which can absorb more power and have similar resistance to bore wear when compared to gray iron. An assembled automotive engine can be made nine percent lighter with CGI. The engine block weight alone can be reduced by 22 percent. This corresponds to a 15 percent reduction in length and a five percent reduction in height and width.This weight savings is made possible by decreasing wall sections less than 4.5 mm thick, where the higher strength and slightly higher stiffness of CGI can be taken advantage of. Similarly, the bore walls and bearing block supports can be reduced in mass without losing the characteristics of gray iron as related to machinability, piston ring wear or noise damping.
Moran told me exactly the same thing: CGI allowed Chevrolet to reduce the block’s wall thickness without compromising strength, resulting in a block about the same weight as the outgoing one despite the new unit being 20 percent larger.
As for the engine’s size, Moran told me the displacement was an intentional way to reduce the specific output (horsepower per liter). This, he told me, lowers exhaust temperatures and pressures, yielding a less-stressed, more durable motor — a quality aided by the fact that the engine makes over 1,200 lb-ft between 1,400 and 2,000 RPM, meaning it can operate at low RPMs almost all the time.
Let’s talk about the new pistons. The outgoing ones were aluminum and the new ones are actually two-pieces of steel laser-welded together under the ring lands (this was done to accommodate a piston cooling gallery). Moran says the new pistons are “appropriately heavier,” though he notes that they’re thinner gauge than the aluminum ones in the outgoing L5P.
“We can run the steel pistons hotter than the aluminum pistons,” he told me. “That gives us improvements from a combustion perspective; it allows us to produce very clean combustion.”
Another change to the new L6P over the the L5P is that there’s now a variable oil pump that can strategically produce oil pressure based on demand, with Moran telling: “It allows us to dial in oil pressure to exactly what the engine needs. We also have electronically controlled piston cooling jets that allows me to cool pistons as needed…When the piston doesn’t need to be cooled, that’s heat that we’re not rejecting to the cooling system that has to go through the oil cooler, etc.”
That oil cooler, by the way, is a giant plate/stack-style heat exchanger now mounted to the side of the motor. The outgoing oil cooler was integrated into the oil filter like this:
Moran says the new heat exchanger has more plates and more cooling capacity than the outgoing one and was “specifically designed for towing 38,000 pounds.”
Moving to the cylinder heads — they’re similar to the outgoing ones in their basic design; they’re aluminum (great for heat dissipation) and they’ve got four valves per cylinder. But the L6P’s heads have integrated intake manifolds.
The outgoing 6.6-liter L5P’s intake manifolds were bolt-ons. Here you can see the intake ports:
And here you can see what the bolt-on manifold looks like (this is a top-view; the intake manifold is at the bottom, and would sit in the vee of the engine with the turbo, just like the current engine):
Moran didn’t get into the advantages of the integrated intake manifold, but I’d guess there are complexity, weight, and potentially thermal management/airflow advantages. Bolted to that intake, in the vee, is a huge turbo.
That larger turbo is spun up by the exhaust exiting the engine on the outside of the vee via two cast iron exhaust manifolds. After spinning up the turbo, some of the exhaust goes to an oxidation catalyst before continuing on to the rest of the exhaust aftertreatment system and some of the turbo’s turbine gases go into the EGR cooler.
The clean air that enters through the engine’s airbox is compressed by the turbo and then sent through two coolers — one liquid-to-air “knock down” cooler and one conventional liquid-to-air charge-air cooler.
If you’re curious what the inside of that knockdown cooler looks like, here you can see a bunch of tubes that the intake air travels through and that are surrounded by cold engine coolant. This is a called a “shell-and-tube” cooler, and in this case is made of stainless steel:
Once through the aluminum charge-air cooler, the air enters the intake ports, but not before being mixed with the appropriate amount of EGR to help reduce emissions.
As for the front of the engine, the alternator, engine fan (not shown), and ac compressor appear to be belt-driven. Otherwise, much of the accessory drive is gear-driven — including the oil pump, water pump, and fuel pump:
Here’s a look at the fuel pump, in case you’re interested:
The injectors are shown here on the right:
There’s a lot more to the engine, but I’m getting sicker at this review goes on, so I’ll leave you with Gale Bank’s look at the motor while I move on to the cooling system and exhaust:
There’s A Huge Cooling Module, And An Impressive Exhaust Aftertreatment
Before I get into the chassis, I’ll finish up talking about the engine ancillaries. The cooling module up front, for example, consists of a transmission oil cooler way at the nose, a condenser next in the stack, then the low-temperature radiator for the charge air cooler (and other things), and then there’s the high-temperature radiator for the engine and whatever else is plumbed into that system (I suspect the EGR cooler).
So that’s what’s in front of the engine. Let’s talk about what’s behind it: a sophisticated aftertreatment system. It begins with the oxidation catalyst I mentioned before. “That really cleans up any unburned fuel/any hydrocarbon coming out of the engine,” Moran told me, pointing to the blue and red wires going to a temperature and NOX sensor.
“Based on the data we get there, we come to our first [diesel exhaust fluid] injector,” he continued. “We dose the DEF here, it goes into the downpipe, mixes with the exhaust flow before we come to the first [selective catalytic reduction] brick.”
“The first SCR takes that DEF, combines it with the exhaust system, reacts to clean up the NOx,” he said, mentioning the larger DEF tank on the new truck compared to the outgoing diesel HD (up from 7 gallons to 9 gallons).
“Once we come out of the SCR, we double check the NOx where we are (he pointed to a blue wire) based on what we cleaned up in the first [SCR brick], before we go into the DPF.”
“[The DPF] is the particulate filter that cleans up the soot emissions in the engine…we measure the delta pressure across the DPF and… we regen the system when needed,” Moran, mentioning that the new Silverado HD now lets the driver regen at idle or manually without requiring a dealer to handle it.
“Based on what we see out of the DPF, we then dose the second DEF injector. That will then mix with the exhaust before we go into the second Selective Catalytic Reduction — there are two bricks in there that clean everything up before [the exhaust] goes to the tailpipe.”
The tailpipe, by the way, is quite cool. I’ve seen this on other diesel trucks but never thought too much of it; it turns out those holes in the tailpipe are there to reduce exhaust tip temperatures. The nozzle visible through the holes is acting as a venturi.
“The hot gas going through the center draws in fresh air from underneath the vehicle to control exhaust tip temperature,” Moran told me.
Big Updates To Brakes And Steering, Suspension Remains Largely The Same
On heavy-duty pickup trucks and really anything with a solid front axle, the way steering works is the intermediate shaft that’s spun by the steering column goes into a steering box. That box’s output is a pitman arm that swings in an arc, pulling and pushing a drag link and tie rod that are attached to the front steering knuckles. It’s a simple, but rather imprecise system, in part because these steering gearboxes have so much slop in them.
The new Silverado is the only HD pickup to use independent suspension — a design that is usually joined by a rack and pinion steering system. Chevrolet kept the old-school system going, presumably for durability reasons, but now for 2027 the brand says rack and pinions are ready for primetime in an HD application.
That makes the Silverado the first heavy-duty pickup in the U.S. to use a rack-and-pinion design like what you see in most passenger cars. There’s no gearbox; there’s simply a rack that’s attached to tie rods (which bolt to the steering knuckles), and there’s a pinion that’s attached to the steering intermediate shaft. You turn the wheel, this turns a small pinion gear, this moves a rack back and forth, and this pushes and pulls the steering knuckles to turn the front tires.
In addition to it being more precise than a steering box, a steering rack can more easily incorporate electric assist, which the new Silverado HD has. This assist could enable more ADAS driver-assist features, since the vehicle’s computer can now theoretically steer the truck using the electric motor in the rack. From Chevy:
Our first-in-class advanced, electrically assisted rack-and-pinion steering system helps give Silverado HD a confident, modern steering foundation, designed for reduced maintenance. Nimbly maneuver turns on switchbacks, squeeze through tight fits at the construction site and back into parking spaces with ease.
Tuned for precise and responsive steering
Quiet operation with no hydraulic noise
Reduces steering kickback off-road
Another major change for the new Silverado HD is the brake system. The rotors are bigger — now 14.6 inches — and they’re squeezed by new four-piston fixed calipers.
Perhaps even more important than the bigger brake hardware is the new eBoost electronic brake boost system. This replaces a hydroboost system that ran off the power steering pump on the old truck’s accessory drive.
The new electronic brake assist (shown below), Chevy says, is meant to offer “responsive and smooth heavy-duty stopping power, helping to give you added confidence when braking under load, especially on long downhill grades or when making repeated stops while towing.” The brand notes that drivers should notice a “More predictable brake feel; smoother, faster brake response; and improved braking power, cooling and consistency.”
As for the rest of the truck, the basic hardware is similar to the outgoing pickup. Out back is a leaf-sprung solid axle:
And up front is an independent front suspension:
Chevy reckons it’s dialed in leaf springs to the point where a move to coils or airbags doesn’t seem worth it. The brand is also happy with its torsion bar front springs that it’s been rocking or many years:
To see how much of a difference that new electronic brake booster and electronic power steering made on everyday drivability, I hit the road — but not before towing an absurd amount of weight with an absolutely epic truck.
Towing 37,000 Pounds In One Of The Most Impressive Trucks I’ve Ever Driven
What you’re looking at may be one of the greatest trucks I’ve ever driven. Why? Because it’s a nice combination of old and new; this red Silverado 3500 is a regular cab dually with a bench seat, column shifter, and vinyl floors. The screen is small, the dashboard plastics are rock hard (just as many workers prefer), and overall it just feels like a real work truck:
The truck is basic, and yet, it’s also equipped with a huge, modern 8.3-liter monster diesel making 1,230 lb-ft of torque.
Using that truck to tow 37,000 pounds down a drag strip was amazing. The jump off the line was a bit slow, but eventually that turbo spooled, the engine built a few revs, and I was on my way accelerating with a colossal load hooked up to the truck’s gooseneck.
The shifts were a bit firm, as one might expect when towing so much weight (it’s possible there was a little slop in the trailer hookup). But otherwise, that Allison 10-speed did a fine job helping the truck accelerate all the way to 60 mph, confidently.
Obviously, I’d prefer a 4×4, but this two-wheel drive “max tow” truck — with its basic interior and regular cab configuration — charmed me. And so did that surprisingly refined 8.3-liter, which — thanks to that turbo and the sheer amount of air passing through the motor — sounded almost like a jet engine as it stormed along that dragstrip.
Climbing A Mountain At 1,500 RPM
Chevrolet had journalists meet in a parking lot outside the hotel at 8 AM. There, a bunch of Silverados were lined up, and I was assigned the black 8.3-liter Duramax you see in the middle here:
Hopping into the truck, my first impressions were solid. The truck I used to tow 37,000 pounds was basic, but this black truck was nicer — but not too nice.
The thing I like most about this Silverado HD in comparison to its sibling, the 1500 that I also drove during this press trip, is that there are more physical buttons and there is a truly substantial column shifter.
Seriously, the shifter feels satisfyingly mechanical, and does a lot to give the Silverado HD a “truckish” feel.
Obviously, it’s that tall Duramax diesel that I was most excited to try out on the street, and again I’ll say: It’s felt remarkably refined. Like I noticed at the drag strip, the sound it makes isn’t violent — it’s a loud whooosh that sounds like all the air the engine is sucking in and shooting out the back. The noise isn’t what I noticed when you drive this truck, though; what I noticed was just how low the engine’s revs stayed all the time.
Here I am accelerating quickly as I pull onto a main road; you’ll notice the RPMs are at 1500:
It makes sense. The torque curve for this behemoth engine is total madness — it makes the outgoing engine look downright pedestrian all across the rev range:
But it’s the bottom of the rev range that blows my mind. At only 1,400 RPM, the engine makes 1,230 lb-ft of torque. This means that, if you’re spinning just 1,400 RPM and you’re mashing the pedal, you can make 328 horsepower. That’s a lot of power at an engine speed that would fall into the “cold idle bump” range of a typical gas engine (i.e. that’s what some gas engines idle at when cold in order to warm up).
Experiencing acceleration from a thoroughly relaxed engine on a flat surface is cool enough, but to experience that on a grade is even more impressive. I literally climbed a steep mountain without the engine ever cresting 2,000 revs. I wish I could tell you more about how the Allison transmission behaves, but it did so little shifting that I’m just going to say it was good:
Throw a load on the back, and the 8.3 is in a league of its own when compared to anything else I drove out there — any of the Silverado 1500 half-ton trucks and the Silverado HD equipped with the 6.6-liter gas motor. That motor is more than competent, but the 8.3 shrugs off whatever you hook up to it, and quickly climbs whatever grade needs to be climbed without even the slightest complaint.
Coming down, the exhaust brake, the transmission braking, and the big discs at all corners mean the vehicle slows down as confidently as it speeds up. The brakes are solid; the pedal travel is a bit shorter than I’m used to, but it felt nice, though at idle, the truck did seem like it almost wanted to push through the brakes (I’ll have more on that later).
The steering, while a rack and pinion setup, doesn’t exactly feel that precise. There’s plenty of play on center, but I don’t mind that on an HD truck; if this thing were as tight as, say, a Cadillac ATS-V steering rack, that would feel out of place. What’s more, the truck’s size and suspension setup means it won’t change directions very fast no matter what you do.
But I’m not criticizing the truck’s handling; it actually slithered through the Arizona mountain roads better than I expected for a large truck. The ride was a little firm, the steering felt very light, and the brakes felt mostly normal. The 2027 Chevy Silverado HD is a shockingly daily-drivable heavy-duty truck that just so happens to have an earth-shattering, torquey 8.3-liter turbodiesel V8.
Off-Roading The Beast
Jumping into the Silverado HD ZR2 almost required a ladder; seriously, the floor height is absolutely bonkers, though I applaud Chevy for putting grab handles on the A-pillars. Every truck should have those.
The Silverado HD gets the job done off-road. It’s got aggressive Goodyear Wrangler tires, lockers front and rear, and skidplates where you need them (though I’d like to have seen protection under the engine and transmission pans, even if I recognize those are tucked up high.
A truck this big isn’t ever going to be a sensational off-roader due to geometry constraints, but the suspension articulated well enough, the tires gripped well (especially with lockers), and I was able to take this thing down a rock trail and have a lot of fun.
I’m not feeling great; I’m definitely going to be out of commission tomorrow, so let me wrap this thing up.
If You Like Trucks, The 2027 Chevrolet Silverado HD Is Epic
I’m a huge truck fan, and I love big, brawny engines. In that context, this new Silverado HD seems, to me, like it has the potential to become one of the great trucks of all time. Yes, the competition will eventually catch up, and that’s great. But until then, Ram and Ford are not only down on power and torque, but their engines are 1.6 liters smaller.
The cheapest Duramax Silverado HD will cost you $62,000 (that’s the base price of about $47,000 plus the $11,400 premium for the diesel). That’s not cheap for a Work Truck, but some might find it worth it in order to own the biggest, baddest pickup truck on American roads today. Then again, you could argue that the biggest, baddest pickup out there is the 1,025 horsepower, 1,198 lb-ft Rivian R1T, which would outperform the Silverado HD in many, many ways. But these are two very different machines, and in the category of ICE trucks, we may have to crown a new king.
Crap, I did end up writing 4,000 words. I’m off to bed.
Top Image: David Tracy
