Heavy-duty diesel power
8.3 liters of turbocharged V8 displacement with published peak output of 555 horsepower and 1,230 lb-ft.
8.3L Mongoose Duramax
Coming to the 2027 GMC Sierra HD
MEET THE
MONGOOSE.
The all-new 8.3L Duramax Turbo-Diesel V8 arrives with 555 horsepower, 1,230 lb-ft of torque and a new chapter in GMC heavy-duty performance.
555Maximum horsepower
1,230Maximum torque · lb-ft
8.3LTurbo-diesel V8 displacement
10Allison-branded transmission speeds
Official General Motors video
THE MONGOOSE HAS ARRIVED.
GM's official teaser introduces the 8.3L Duramax under its Mongoose nickname, a reference to the animal known for hunting scorpions. The engine is slated for refreshed 2027 GMC Sierra HD and Chevrolet Silverado HD trucks.
Select the video preview to watch it directly on YouTube. This avoids embedded-player errors on Dealer.com.
2027 Duramax engine specifications
MORE DISPLACEMENT. MORE OUTPUT.
The L6P Mongoose expands Duramax displacement from 6.6 to 8.3 liters, with meaningful gains over the outgoing L5P's published output. GMC pairs the new diesel with an Allison-branded 10-speed automatic transmission.
+85 HP555 vs. 470 horsepower · approximately 18% increase
+255 LB-FT1,230 vs. 975 lb-ft · approximately 26% increase
10-speed automatic
The new diesel is paired with an Allison-branded 10-speed automatic transmission.
Coming to Sierra HD
The Mongoose is coming to the refreshed 2027 GMC Sierra HD lineup.
Published engine-output comparison
HOW THE NUMBERS COMPARE.
A side-by-side look at published engine ratings for the new Mongoose, the previous Duramax and competing heavy-duty diesels. These are engine figures—not truck-specific towing or payload ratings.
| Specification | NEW Duramax L6P | Previous Duramax L5P | Ford Power Stroke | Ford H.O. Power Stroke | Ram H.O. Cummins |
|---|---|---|---|---|---|
| Truck family | 2027 GMC Sierra HD | GMC Sierra HD | Super Duty | Super Duty | Ram HD |
| Configuration | Turbo-diesel V8 | Turbo-diesel V8 | Turbo-diesel V8 | Turbo-diesel V8 | Turbo-diesel I6 |
| Displacement | 8.3L | 6.6L | 6.7L | 6.7L | 6.7L |
| Horsepower | 555 | 470 | 475 | 500 | 430 |
| Torque (lb-ft) | 1,230 | 975 | 1,050 | 1,200 | 1,075 |
Comparison reflects published ratings reported September 24, 2026. Availability, calibration and configurations may vary by model year. The new L6P's horsepower and torque peak RPM figures had not been released at the time of publication.
Beyond the new engine
WHAT ELSE IS NEW FOR 2027?
The refreshed GMC Sierra HD is also reported to receive upgrades intended to improve steering feel, trailering functionality, thermal management and everyday drivability.
- Rack-and-pinion electric power steering
- Electronic brake-boost system
- Upgraded drive modes
- Enhanced integrated trailering technology
- New cooling technology and refinement updates
- Updated 6.6L gasoline V8 option (L8S)
Equipment and feature availability by trim and configuration have not all been announced.
What we know—and what is still coming
2027 SIERRA HD DETAILS ARE STILL DEVELOPING.
As of September 24, 2026, the new 8.3L diesel's maximum horsepower, torque, displacement and transmission pairing have been reported. GMC has not yet published complete model-by-model towing and payload ratings, engine peak-output RPM, final pricing or dealer arrival dates. Check back as additional official specifications are released.
Find your next heavy-duty GMC
READY FOR WHAT'S NEXT?
Explore our current Sierra HD inventory or contact our team to learn more about upcoming 2027 model information.
Explore available Sierra HD inventory today. Information about future 2027 availability will be shared when announced; no vehicle reservation or availability is implied.
Information current September 24, 2026. Sources: GM Authority, September 24 engine-output report; General Motors, September 21 Mongoose announcement. Cole Buick GMC dealership editorial summary. Video thumbnail links to the supplied YouTube video; no embedded player is used.