GM’s New 8.3L Duramax: Codename Mongoose

GM has confirmed an all-new 8.3L Duramax turbo-diesel V8, code-named Mongoose, for the refreshed 2027 Chevrolet Silverado HD and GMC Sierra HD. The company revealed the engine in a teaser video on September 21, 2026, but has not yet released horsepower, torque or towing figures.

It is the biggest change to GM’s heavy-duty diesel lineup in decades. Every Duramax V8 offered in GM’s heavy-duty pickups since the 2001 model year has displaced 6.6 liters, so the jump to 8.3 liters signals that GM intends to take the power lead back from Ford and Ram.

Here is what GM has confirmed, what is still speculation and what the new engine means if you own, plan to buy or plan to sell a truck with the current 6.6L L5P Duramax.

What is the 8.3L Duramax?

The 8.3L Duramax is GM’s next-generation turbo-diesel V8 for its heavy-duty pickups, and it is the largest diesel GM has ever put in a Silverado HD or Sierra HD.

At 8.3 liters, it displaces roughly 506 cubic inches, about 26% more than the 6.6L L5P it follows. GM calls it “all-new,” which means this is not a stroked or bored version of the current engine. GM describes the Mongoose as “built to dominate,” and the teaser makes it clear the engine was designed to beat the competition on output.

What has GM confirmed about the 8.3 Duramax?

GM has confirmed only the displacement, the engine configuration, the nickname and the two trucks that will use it.

Confirmed by GM	Not yet announced
8.3L turbo-diesel V8	Horsepower and torque
Duramax branding, code-named Mongoose	Towing and payload ratings
2027 Chevrolet Silverado HD	Transmission pairing
2027 GMC Sierra HD	Production plant
First look released September 21, 2026	On-sale date and pricing

GM’s announcement described the teaser as a first look and said Chevrolet and GMC will have more to share soon. Until then, treat any specific power figure you see online as an estimate.

How much horsepower will the 8.3 Duramax make?

GM has not released horsepower or torque figures for the 8.3L Duramax yet.

To claim the class lead, the Mongoose needs to beat Ford’s high-output 6.7L Power Stroke at 500 hp and 1,200 lb-ft of torque. Some industry coverage speculates the new engine will land at around 600 hp and 1,400 lb-ft, but GM has not confirmed those numbers. Here is where the current heavy-duty diesels stand:

Engine	Horsepower	Torque
Ford 6.7L Power Stroke High Output	500 hp	1,200 lb-ft
GM 6.6L L5P Duramax (2024 and newer)	470 hp	975 lb-ft
Ram 6.7L Cummins High Output	430 hp	1,075 lb-ft
GM 8.3L Duramax Mongoose (2027)	Not announced	Not announced

The L5P has trailed Ford’s Power Stroke on torque since it launched for the 2017 model year, which is a big part of why GM went bigger rather than turning up the current engine.

Codename – Mongoose

GM named the engine Mongoose as a direct shot at Ford, whose Power Stroke diesel development carried the nickname Scorpion.

The teaser video shows a mongoose taking on a scorpion, and in the wild, the mongoose wins. It is one of the most pointed pieces of competitive marketing in the heavy-duty truck segment in years, and it tells buyers exactly which truck GM is benchmarking against.

Will the 8.3 Duramax replace the 6.6L L5P?

GM has not officially said whether the 8.3L will replace the 6.6L L5P, but early signs point that way.

GM Authority reports that dealer order guides list only one diesel engine option for the 2027 Silverado HD and Sierra HD. If that holds, the L5P, which has powered GM’s heavy-duty pickups since the 2017 model year, would end production after the 2026 model year. That would make 2017 to 2026 trucks the final generation of the 6.6L Duramax.

When will the 8.3 Duramax be available?

The 8.3L Duramax will debut in the 2027 Chevrolet Silverado HD and GMC Sierra HD, but GM has not announced an on-sale date.

Full specifications, pricing and trim availability should arrive with the official reveal of the refreshed 2027 trucks. We will update this article as GM releases more details.

What does the 8.3 Duramax mean for used L5P trucks?

For most buyers, the arrival of the 8.3L Duramax makes a proven, used L5P truck an even more practical choice while the new engine builds its track record.

Any all-new engine starts with no long-term reliability history, and many fleet managers and contractors wait a few model years before committing to one. The L5P, by contrast, has close to a decade of real-world data behind it. Trucks from 2017 to 2023 produce 445 hp and 910 lb-ft, while 2024 and newer models produce 470 hp and 975 lb-ft. Trucks from the 2020 model year onward also pair the engine with the Allison 10-speed automatic.

If you are shopping for an L5P truck, focus on service records, emissions system history and how the truck was used, since towing, idling and short trips all wear a diesel differently. Our guide to Duramax reliability by generation covers what to check on each engine, and our look at Chevy’s longest-lasting pickup truck engines covers where the Duramax fits in GM’s lineup.

If you are buying or selling, recent auction results are the clearest picture of what L5P trucks are worth as news about the Mongoose develops. You can compare condition reports and current listings on the Ritchie Bros. used pickup trucks page, with transparent, market-driven pricing on every sale.

The bottom line

The 8.3L Duramax Mongoose is GM’s bid to reclaim the heavy-duty diesel crown, and on displacement alone it is the biggest engine in the segment. Until GM releases official power, towing and pricing figures, the smart move is to follow the confirmed facts, watch the market and lean on proven powertrains for work that cannot wait.

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