GM Mongoose 8.3L Duramax: 1,230 lb-ft for 2027 HDs

The 8.3-liter Mongoose Duramax turbo V8 will deliver 1,230 pound-feet of torque in GM's 2027 Chevrolet Silverado HD and its GMC twin, the company confirmed.

GM says the Mongoose-equipped trucks will produce 555 horsepower and 1,230 lb-ft of torque (563 PS and 1,667 Nm), figures the automaker positions as best in class for production heavy-duty diesel pickups. The new V8 is the largest truck engine GM has fitted since the Vortec 8100 gasoline V8 and represents GM's first heavy-duty diesel both developed and manufactured in-house.

The Mongoose 8.3L Duramax is a turbocharged V8 built with steel pistons, a forged crank and rods, and a compacted graphite iron block, and GM rates it at 555 hp and 1,230 lb-ft—the highest diesel torque figure for a production heavy-duty truck.

Powertrain details and towing capability

GM says the engine uses a single variable-geometry turbo, a dual-stage air-to-water charge-cooling system, revised aftertreatment, and high-flow injectors. The powerplant pairs with a 10-speed automatic GM calls the 10L1000. That 10L designation refers to a 10-speed family developed in a joint venture with Ford; GM notes the unit is not a true Allison transmission. Genuine Allison units remain available only on medium-duty models such as the 4500-series, where an Allison-branded transmission has six gears rather than 10.

With the Mongoose and proper equipment, GM's 2027 heavy-duty trucks are rated to tow up to 20,000 pounds (9,072 kilograms) conventionally and up to 38,000 pounds (17,237 kilograms) with a gooseneck; dually models with the 8.3-liter engine are rated at 30,000 pounds or more. Gross combined weight rating peaks at 46,500 pounds (21,092 kilograms). Ford retains the single-vehicle maximum towing figure of 40,000 pounds (18,144 kilograms) with its F-450 XL Regular Cab 4x2 DRW when fitted with the high-output Power Stroke and High-Capacity Gooseneck Tow Package.

Complementary engines, manufacturing, and chassis changes

Alongside the Mongoose, GM lists an enhanced 6.6-liter small-block gasoline V8 in the order guide under the code L8S. The L8S is rated at 412 horsepower and 472 pound-feet (640 Newton-meters) and gains a Turbo-Jet intake manifold, an engine-mounted oil cooler, revised lubrication, and a digital oil level display. GM says Tonawanda Assembly builds the gasoline L8S, while the 8.3-liter Duramax is produced at the DMAX facility in Brookville, Ohio.

For 2027, the heavy-duty line also abandons hydraulic steering broadly in favor of rack-and-pinion electric power steering, which GM describes as a segment first and claims delivers roughly 30 percent more steering output than the previous hydraulic system. Braking is also electrically actuated for the first time in the segment, using 14.6-inch (371 millimeter) front rotors with four-piston fixed calipers, shorter pedal travel, and diagnostics designed to detect fade or leaks before the driver notices them.

Off-road-focused ZR2 and AT4X trims gain a new Terrain Mode that enables one-pedal driving in 4HI and 4LO; lifting off the accelerator engages engine and driveline braking to control descents. Tow/Haul and Off-Road calibrations have been retuned across the range, and up to 14 camera views, including a Transparent Trailer mode, are available to aid hitching and maneuvering.

GM reports more than 60 percent of its heavy-duty truck customers choose diesel and that its brands already hold the majority share of the segment's diesel market. The 2027 Silverado HD and GMC counterparts are due at dealers later this year, with pricing to be announced closer to launch. The order guide for 2027 does not list the outgoing L5P Duramax, and GM has left its future in the lineup open.