Just a few days ago, General Motors teased the introduction of its biggest combustion engine ever (at least for a car or truck sold to the public). It also talked up some impressive performance improvements. Now, the General has revealed all the key specifications, and the monster diesel is, indeed, the new power and torque king of the heavy duty pickup truck class.
GM didn’t stop there, though, as it also upgraded the steering, brakes, and even the gas V8 option to make the Chevy Silverado HD and GMC Sierra HD more impressive than ever before.
Mostly complete Duramax 8.3-liter engines move through the factoryGeneral Motors
The Mongoose Beats The Scorpion On Paper
For the last few years, Ford has been at the top of the heap when it comes to factory diesel performance with its high-output PowerStroke V8, nicknamed “Scorpion” making 500 horsepower and 1,200 pound-feet of torque. GM managed to top the benchmark, but perhaps not by as much as you would expect for having an extra 1.6 liters of displacement. The 8.3-liter GM Duramax engine named “Mongoose” makes 555 hp and 1,230 lb-ft. The horsepower is obviously the more impressive improvement over the Ford, with torque being less so. Buyers going from the old Duramax to this one, though, will be bowled over, as the old engine made 470 hp and 975 lb-ft of torque.
The front of a Duramax 8.3-liter engineGeneral Motors
GM didn’t just add displacement to hit its power numbers, though. The new diesel features a compacted-graphite iron block, and fully forged steel internals (crankshaft, connecting rods, and pistons). Engine cooling has been improved, and the variable-geometry turbocharger feeds boost through a new dual-stage air-to-water intercooler. Power still goes through GM’s 10-speed Allison automatic transmission.
2027 Chevrolet Silverado HD 2500 Z71 from the front three-quarter angleChevrolet
The diesel also provides the Silverado HD and Sierra HD with improved towing capacity. Maximum capacity in the right configuration fifth-wheel setup now reaches 38,000 pounds. That’s better than the Ram 3500, and ties the Ford F-350 Super Duty. The F-450 Super Duty still wins out with more than 40,000 pounds of towing capacity with a fifth-wheel trailer. As for conventional towing, the new GM trucks top out at 20,000 pounds. That means that Ford is still the king with a normal bumper-located hitch with up to 28,000 pounds of capacity.
What Else Did GM Upgrade?
If you’re not interested in a diesel, especially with current fuel prices, GM gave the current 6.6-liter gas V8 some love, too. It changed the intake manifold and oil cooler setup, plus improved some of the lubrication system. With these detail updates, power increased from 401 to 412 hp, and torque increased from 464 lb-ft to 472. That means GM’s gas V8 makes more torque than those from Ram and Ford, even though the Ford has an extra 0.7 liters of displacement. Though the Ford still takes the horsepower prize.
Stopping and steering capabilities should be even better now, too. GM heavy-duty pickups get improved brakes with the front discs now measuring 14.6 inches in diameter, and they get fixed four-piston calipers. GM also switched the systems to use an electronic brake booster. As for steering, it’s dropped hydraulic assist altogether for an electric assist system. GM touts reduced complexity and part count, and combined with the rack-and-pinion steering setup, it should be far more accurate and precise than the recirculating-ball designs used by Ford and Ram.
Two 2027 GMC Sierra HDs parked side by sideGMC
Finally, GM added a new drive mode for the ZR2 and AT4X off-road versions of its heavy-duty trucks. They get a Terrain Mode on top of the existing Off-Road Mode. This mode allows for one-pedal driving off-road in both low and high four-wheel-drive settings.
2027 Chevrolet Silverado HD 2500 ZR2 from the front three-quarter angleChevrolet
CarBuzz Insight – Why This Matters:
GM’s heavy-duty diesel trucks have lagged behind Ford and Ram in raw specifications for a while now. Even if those sheer numbers don’t make the biggest difference in actual driving, truck shoppers do tend to care about having the biggest, baddest brute around.
So, between having a more impressive spec sheet, and providing a noticeable improvement in performance over the old model, long-time and new GM truck buyers should find something to like in the new diesel.
