General Motors Unveils 8.3-Liter Mongoose Diesel Engine for 2027 Trucks

General Motors revealed a new 8.3-liter Duramax turbodiesel V8 engine, codenamed Mongoose, for the 2027 Chevrolet Silverado HD and GMC Sierra HD. The engine replaces the 6.6-liter Duramax and represents a 26% increase in displacement. While initially teased without specifications, GM later confirmed the engine produces 555 horsepower and 1,230 pound-feet of torque, surpassing competing engines from Ford and Ram.

The powertrain, which carries the RPO code L6P, is paired with an Allison-branded 10-speed automatic transmission. It enables a maximum gooseneck towing capacity of 38,000 pounds, though this remains below Ford's 40,000-pound maximum. To support the launch, GM invested $920 million into production facilities in Ohio earlier this year.

Beyond the diesel engine, GM updated the standard 6.6-liter gas V8 to 412 horsepower and 472 pound-feet of torque. The 2027 models introduce segment-first technologies, including an electronic brake-boost system and rack-and-pinion electric power steering, alongside hardware upgrades like four-piston fixed front calipers. The trucks are expected to arrive at dealerships in late 2026.