The 2027 Chevy Silverado HD and GMC Sierra HD Debut a Gigantic 8.3L Diesel Engine Called MongooseCar and DriverJack FitzgeraldThu, September 24, 2026 at 3:08 PM UTCAdd us on GoogleGM's New HD Trucks Debut a Huge Diesel V-8General MotorsGeneral Motors has revealed a new Chevrolet Silverado HD and GMC Sierra HD, which have been significantly refreshed for the 2027 model year.The heavy-duty trucks get new engines, including a diesel 8.3-liter V-8 with 1230 pound-feet of torque, and they adopt an electric rack-and-pinion setup.The new HD trucks are expected to go on sale by the end of the year, with prices to be released before that time.When looking at the refreshed versions of the heavy-duty Chevrolet Silverado and GMC Sierra, we can't help but think of the Fiat S76. Built in 1910, the S76 is better known as "The Beast of Turin." It earned that moniker because of its 28.3-liter four-cylinder engine that sounds like a chained eldritch beast. These new GM workhorses, many of which will be powered by the company's new diesel 8.3-liter V-8, could use a nickname as well. We haven't heard the new engine—officially called Mongoose—roar yet, but maybe "Devil of Detroit" will work.General MotorsThe new massive-displacement Duramax diesel will serve as an optional engine on both the Silverado HD and Sierra HD. As the new flagship engine, the Mongoose produces 555 horsepower and 1230 pound-feet of torque. It'll be joined by an updated gas-slurping 6.6-liter V-8, which now generates 412 horses and 472 pound-feet. The gasser benefits from a new turbo-jet intake manifold that GM tuned specifically for HD performance. This powertrain also receives better cooling and lubrication under load, which is helpful since these HD pickups are often towing something. Both engine options are connected to an Allison 10-speed automatic transmission.AdvertisementAdvertisementOf course, the new trucks don't get power increases for nothing. Towing figures are up too. Naturally. The HD's maximums have risen to 20,000 pounds with a conventional trailer hitch, while models equipped with a gooseneck setup can now lug up to 38,000 pounds. Every diesel truck configured with a dual-rear-axle setup can now tow at least 30,000 pounds. While the 2500 maxes out at 23,200 pounds, opting for the crew cab drops that figure to 22,400.General MotorsThe new trucks should also feel better behind the wheel. GM has finally ditched the old recirculating-ball steering found on every other heavy-duty truck and switched to an electrically assisted rack-and-pinion setup. Not only does the new system have about 30 percent more power than the outgoing hydraulic setup, according to GM, but it should offer much more precise steering. The first-in-the-segment steering is joined by a first-in-the-segment electronic brake-boost system.Speaking of stopping power, the new GM trucks come with 14.6-inch front rotors, four-piston front calipers, and updated hardware for the rear brakes. The new brakes can take more heat and—coupled with a new pedal placement and more linear brake travel—should improve confidence while hauling heavy loads.GM says the new 2027 Chevy Silverado HD and 2027 GMC Sierra HD trucks are expected to arrive by the end of the year. Pricing hasn't yet been announced, but we shouldn't have to wait too long, considering that the new year is quickly approaching.➡️ Skip the lot. Let Car and Driver help you find your next car.Shop New Cars Shop Used CarsYou Might Also LikeGift Guide: Best Ride-On Electric Cars for KidsFuture Cars Worth Waiting For: 2025–2029