GM's 8.3L Duramax HD Diesel Enters Flint Assembly Now

GM Trucks reports Flint Assembly in Michigan will begin producing the 2027 Chevrolet Silverado HD and GMC Sierra HD equipped with the optional 8.3-liter Duramax diesel on Monday, November 16. The plant is finishing 2026 turbo diesel production and will move straight into the new- model run.

Flint assembles the 2500 and 3500 Silverado HD and Sierra HD, including dual-rear-wheel variants. General Motors says both 2027 heavy-duty models will launch in the latter part of 2026, and GM also continues HD truck assembly at its Oshawa, Canada facility. The new 8.3-liter Duramax is built at DMAX in Ohio.

Powertrain details and capability

The 8.3-liter diesel, internally designated L6P and referred to in some materials as the Mongoose engine, is a clean-sheet design that GM rates at a best-in-class 555 horsepower and an estimated 1,230 pound-feet of peak torque, or 1,668 Newton-meters. Compared with the outgoing L5P, the L6P adds about 85 horsepower and 255 pound-feet, which translates to modestly higher maximum towing numbers.

GM quotes a 2027 diesel option price of $11,400, up from $9,900 for the predecessor engine. The L6P uses a compacted graphite iron block and accepts B20 biodiesel. It is paired with a 10-speed automatic transmission carrying Allison branding despite not being a true Allison unit. The engine features forged connecting rods, a forged crankshaft and forged pistons, a variable-geometry turbo, dual-stage air-to-water charge cooling, piston-cooling oil jets, a variable-displacement oil pump and updated exhaust after-treatment hardware.

Chevrolet lists a maximum available towing capacity of 38,000 pounds, or 17,237 kilograms, and a maximum payload of 6,170 pounds, or 2,799 kilograms, for the Silverado HD when equipped with the diesel. Choosing the 6.6-liter gasoline V8 reduces maximum towing to 19,000 pounds and gives a 6,990-pound payload, figures equivalent to 8,618 and 3,171 kilograms respectively.

The gasoline engine in the heavy-duty range carries the L8S production code, replacing the former L8T. Assembled in Tonawanda, New York, the 6.6-liter naturally aspirated V8 is tuned to 412 horsepower and 472 pound-feet, or 640 Newton-meters, on regular unleaded fuel. Key differences from the previous gasser include a redesigned intake manifold, an upgraded cooling system with a new water pump and revised internal oil passages, a different oil pan and a digital oil level display in the instrument cluster instead of a dipstick.

Both diesel and gasoline powertrains are paired with rack-and-pinion electric power steering. For model year 2027, GM has also added an electronic brake-boost system and updated Tow/Haul and Off-Road drive modes across the HD range. Dealers are expected to offer end-of-production incentives on remaining 2026 inventory as the factory transitions to the 2027 run.

The 8.3-liter Duramax L6P that begins assembly November 16 is produced at DMAX in Ohio, completing the factory-level picture for the updated heavy-duty lineup.