GM Unleashes 8.3L Duramax V8 with 555 HP and 1,230 LB-FT for 2027

General Motors just released updates for the 2027 Chevrolet Silverado HD and GMC Sierra HD.

Leading the news is an all-new, clean-sheet 8.3-liter Duramax turbo-diesel V8 engine. Built entirely in-house, the new flagship diesel churns out a best-in-class 555 horsepower and an earth-moving 1,230 lb-ft of torque. Just in time for diesel to hit 8 bucks a gallon.

Clean-Sheet Diesel Engine and Updated Gas V8

The 8.3-liter Duramax V8 is GM’s first ground-up heavy-duty diesel redesign in decades.

Built around a compacted graphite iron cylinder block with a fully forged crankshaft, forged connecting rods, and steel pistons, the engine was designed to handle the extreme thermal and mechanical stress that happens under heavy workloads. A dual-stage air-to-water charge cooling system works alongside a high-efficiency variable-geometry turbocharger to maintain power during prolonged grade climbs.

The new diesel engine will be manufactured at GM's expanded 1.4-million-square-foot DMAX facility in Brookville, Ohio.

The standard 6.6-liter gas V8 has also been updated, gaining a new intake manifold, revised lubrication system, and an engine-mounted oil cooler. Output rises to 412 horsepower and 472 lb-ft of torque. This is not the same 6.6-liter L78 V8 just given to the Silverado and Sierra 1500s for 2027.

Both engines pair with an Allison 10-speed automatic transmission. When properly equipped, 2027 models will be able to drag up to 20,000 pounds using a conventional hitch and up to 38,000 pounds for goosenecks. The maximum Gross Combined Weight Rating (GCWR) is 46,500 pounds.

Electric Power Steering and Electronic Brake-Boost

GM is ditching traditional heavy-duty hydraulic steering hardware for a segment-first rack-and-pinion Electric Power Steering (EPS) system. The new EPS setup delivers roughly 30 percent more steering power output than the outgoing hydraulic gear, making tight low-speed maneuvers with a trailer substantially easier while cutting road kickback and eliminating hydraulic pumps and hoses.

There's a new electronic brake-boost system that replaces the old hydro-boost design. The system works alongside larger 14.6-inch front rotors and four-piston fixed front calipers to improve pedal feel and stopping consistency while hauling. The hardware updates should reduce brake pedal travel, improve pedal feel with heavy loads, and integrate better with safety features like Adaptive Cruise Control and Automatic Emergency Braking.

Heavy Duty Drive Modes and One-Pedal Off-Roading

The 2027 Silverado HD and Sierra HD also gain updated drive modes.

Normal mode is normal and manages everyday driving, while Tow/Haul adjusts shift timing, exhaust braking, and brake-boost response for heavy loads. Off-Road mode will modify the traction control and stability systems for loose terrain.

For off-road trucks like the ZR2 and AT4X, a new Terrain Mode will allow for one-pedal driving in both 4HI and 4LO. This setup automatically applies the foundation brakes when the driver lifts off the accelerator pedal during low-speed, technical off-road driving.

The 2027 Chevrolet Silverado HD and GMC Sierra HD are expected to arrive at U.S. dealerships in late 2026. Pricing and complete package details will be announced closer to launch.

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