The new 8.3-liter Duramax produces 555 hp and 1,230 lb-ft of torque. GM also replaces hydraulic steering and brake assist with electric systems. Maximum gooseneck towing rises to 38,000 pounds, still shy of Ford’s 40,000. Heavy-duty pickups have spent years fighting over ever-increasing numbers, and GM just landed a substantial blow. Its 2027 Chevrolet Silverado HD and GMC Sierra HD will offer an all-new 8.3-liter Duramax turbodiesel V8 with 555 hp (414 kW) and 1,230 lb-ft (1,668 Nm) of torque. That beats Ford’s high-output Power Stroke on both figures. Yet the biggest surprise here may be how much GM changed around the engine. The new diesel replaces the familiar 6.6-liter Duramax, which offered 470 hp (350 kW) and 975 lb-ft (1,322 Nm) in the 2026 Silverado HD. That’s an increase of 85 hp and 255 lb-ft, or roughly 18 and 26 percent, respectively. GM calls the 8.3-liter a clean-sheet, in-house design, rather than a development of an existing engine. Read: Ford’s 6X6 Ranger Super Duty Is Bidding To Arm The British Army There’s plenty for engine nerds to unpack. The new turbodiesel V8 uses a compacted graphite iron block, a fully forged crankshaft and connecting rods, and forged steel pistons. GM also specifies high-flow fuel injection, a variable-geometry turbocharger, and a compact, dual-stage air-to-water charge-cooling system. An integrated intake and crankshaft isolation hardware are intended to tame noise and vibration. A stronger exhaust-braking strategy addresses the less glamorous reality of hauling a huge trailer. Both the diesel and the updated gas V8 use GM’s Allison 10L1000 ten-speed automatic transmission. The gas engine remains a 6.6-liter unit, but a new intake manifold, revised lubrication, an engine-mounted oil cooler, and updated emissions hardware bring it to 412 hp (307 kW) and 472 lb-ft (640 Nm). That’s a modest gain of 11 hp and 8 lb-ft over the previous 401-hp, 464-lb-ft rating. GM’s maximum gooseneck rating climbs from 36,000 to 38,000 pounds (16,329 to 17,237 kg), with conventional towing rated up to 20,000 pounds (9,072 kg). The new diesel tops Ford’s 500-hp, 1,200-lb-ft Power Stroke, but Ford still advertises a 40,000-pound (18,144-kg) gooseneck maximum. Peak engine output and maximum tow ratings are different contests, and these numbers apply to specific configurations. A Different Way To Steer And Stop The chassis changes deserve nearly as much attention. GM is replacing its HD trucks’ hydraulic steering with rack-and-pinion electric power steering, claiming approximately 30 percent more steering output than the old gear. It also replaces the shared hydraulic source for steering and brake assist with an electronic brake booster. Up front are 14.6-inch (371-mm) rotors and four-piston fixed calipers. That separation could matter when maneuvering a loaded truck at low speed because steering assist no longer depends on engine speed or brake-assist demand. GM says the new hardware also allows steering and braking behavior to change with the drive mode. On ZR2 and AT4X models, a new Terrain Mode can automatically apply the brakes as the driver lifts off the accelerator, in either 4HI or 4LO. The 2027 trucks are due at US dealers late this year. GM hasn’t announced prices, engine-speed figures for peak output, or detailed ratings by configuration. Those details will tell buyers more about how much of that headline torque they can actually use. And perhaps most importantly, what it costs to get it. Photos: GM
