2027 Chevrolet Silverado HD and GMC Sierra HD: 8.3-liter Duramax Mongoose diesel

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Rumors about General Motors' huge diesel have finally stopped being rumors. The company has officially confirmed a new 8.3-liter Duramax Turbo-Diesel V8 that will become one of the key technical updates for the 2027 Chevrolet Silverado HD and GMC Sierra HD.

The new engine is called Mongoose. The choice is clearly aimed at Ford: the rival's 6.7-liter Power Stroke diesel is known by the codename Scorpion. In GM's teaser, the company directly plays up the mongoose-versus-scorpion theme, while keeping the technical specifications under wraps.

The one confirmed number is already telling. The current 6.6-liter Duramax V8 produces 470 hp and 975 lb-ft of torque, or 1,322 Nm. Moving to 8.3 liters adds 1.7 liters of displacement, roughly 25.8%. That does not mean power or torque will rise by a similar percentage: GM has not announced either figure yet.

Earlier reports about the engine were also contradictory. Until recently, the 8.3-liter Duramax was unofficially referred to in specialist publications as MegaMax and was rumored to make around 600 hp. The engine itself is now confirmed, but the 600-hp figure has no official status. GM has also not announced an engine code or said whether the current 6.6-liter Duramax will remain in the lineup alongside it.

Full specifications are promised later. Power, torque and maximum trailer rating will show why GM decided to increase Duramax displacement by almost 26%, beyond making a dramatic response to Ford.