GM’s Huge 8.3-Liter ‘Mongoose’ Diesel for Chevy and GMC’s HD Trucks Cranks Out 1230 LB-FT of TorqueRoad & TrackZac PalmerThu, September 24, 2026 at 2:00 PM UTCAdd us on GoogleGM's 'Mongoose' Summons 1230 LB-FT of TwistAJ MASTThe 2027 Chevrolet Silverado HD and GMC Sierra HD trucks may look the same as the last model year, but they sure won't drive the same as before. On Thursday, General Motors revealed a clean-sheet, in-house-designed 8.3-liter Duramax turbodiesel V-8 and both an electric power steering system and electronic brake-boost system for its Heavy Duty pickups.Starting with the Mongoose, which is how GM refers to the enormous diesel engine—well, the transparent size of it is simply mind-boggling. Both the Ram Cummins and Ford Power Stroke heavy duty diesel engines are 6.7-liter units; this 8.3-liter Duramax engine positively blows those out of the water when it comes to displacement. It also wins the horsepower and torque war. GM says the Mongoose produces an eye-popping 555 horsepower and 1230 pound-feet of torque. It doesn't win by much, but that's 30 pound-feet more than the High Output version of Ford's Power Stroke diesel V-8, and a win is a win.AJ MASTThe big story with this 8.3-liter is that it's the first heavy duty truck engine that GM engineered and designed entirely in-house. It's a hardy sucker, with a graphite iron block and forged crankshaft, connecting rods, and steel pistons. GM brags of its dual-stage air-to-water cooling system, new variable-geometry turbocharger, integrated intake, and crankshaft isolation hardware that aims to reduce noise and vibration. Max towing with this new diesel engine sits at 38,000 pounds with a gooseneck, or 20,000 with a conventional hitch.AdvertisementAdvertisementThis new engine is paired with the Allison 10-speed automatic transmission, an upgraded exhaust brake, and new diesel after-treatment layout. It will be built at GM's Brookville, Ohio facility, and serve as the upgrade option to the base gas-powered 6.6-liter V-8. Not to be confused with the Gen 6 LS6 Small Block, this 6.6-liter V-8 is an upgraded version of the powertrain on offer today. For 2027, it produces 412 horsepower and 472 pound-feet of torque—minor increases on both accounts (11 horses and 8 pound-feet of torque), but we're not complaining about more power. GM says a new intake manifold helped achieve the jump; the engine is also treated to a revised lubrication system, engine-mounted oil cooler, and new digital oil-level display.What may be even more impactful on the way these Heavy Duty trucks drive is the new rack-and-pinion electronic power steering system. GM is doing away with the old hydraulically-assisted recirculating ball steering and bringing its HD trucks into the modern age of steering with this update. The hope is to create a real selling point compared to the Ford and Ram competition, which still use classic hydraulic systems.Eliminating hydraulic pumps, hoses, and fluid should reduce noise and complexity in the engine bay. GM promises improved on-center feel, reduced kickback, and significantly easier low-speed maneuverability and towing with this system. The change from recirculating ball to rack-and-pinion should theoretically make the trucks feel more agile and responsive to inputs, too. We won't expect the same feeling as a light duty pickup, but these HD trucks should be much better to drive in every environment.GMFor even more driving refinement, we look to GM's next big update: brake-by-wire. Yet another first for the segment, this electronic brake-boost system should significantly improve the braking experience in GM's HD pickups. Noted improvements include reduced pedal travel, a new (more typical) pedal position, and a more refined pedal feel. These electronics also provide GM the ability to offer more advanced driver assistance systems on its HD trucks like adaptive cruise control and automatic emergency braking.AdvertisementAdvertisementThe braking hardware itself is also being upgraded, as GM moves up to a four-piston fixed front caliper and larger 14.6-inch front rotors. This also means the standard wheel size moves up from a 17-inch to an 18-inch wheel to fit the new, bigger brakes. The rear brakes feature upgraded hardware, too, all in an effort to increase thermal capacity and stiffness when towing heavy loads.Off-road performance is even gaining a bonus feature with one-pedal driving on the Silverado ZR2 and Sierra AT4X. Put the trucks in their new Terrain Mode, and lifting off the accelerator will apply the brakes / function like an EV's one-pedal mode at low speeds. The various drive modes are now custom-tuned even further, thanks to the new electronic systems for both the steering and brakes. A Tow/Haul mode activates a specific tune for the steering and brake control; the same can be said for Off-Road mode that tries to cut out the harsh feedback through the wheel one would previously sense.Both the 2027 Silverado HD and Sierra HD are expected to arrive in dealers in late 2026. Pricing will be revealed closer to the on-sale date.You Might Also LikeIf You Can Only Own One Car, Make It One of TheseThese Are the Most Popular Cars by State