GM's New 8.3L Duramax Beats Ford and Ram on Paper — Here's What Else Changes

General Motors has put a number on its new diesel, and it clears the bar Ford set. The 8.3-liter Duramax V8 for the 2027 Chevrolet Silverado HD and GMC Sierra HD is rated at 555 hp and 1,230 lb-ft of torque, according to GM. Yet the changes owners notice most may come from the steering and brakes, not the engine.

The spec reveal on September 24 followed GM's mongoose-versus-scorpion teaser from three days earlier, which was widely read as a shot at Ford's Power Stroke.

How the numbers stack up

Compared with the 6.6-liter L5P Duramax that GM currently rates at 470 hp and 975 lb-ft, the new V8 adds 85 hp and 255 lb-ft. That is roughly 18 percent more power and 26 percent more torque. Here is how the top diesel in each 2027 heavy-duty lineup compares:

• GM 8.3L Duramax V8: 555 hp, 1,230 lb-ft, Allison 10-speed automatic, up to 38,000 pounds gooseneck
• Ford 6.7L High-Output Power Stroke V8: 500 hp, 1,200 lb-ft, up to 40,000 pounds gooseneck
• Ram 6.7L Cummins High-Output inline-six: 430 hp, 1,075 lb-ft, eight-speed automatic, up to 37,020 pounds (Ram 3500)

The horsepower lead over Ford is a clear 55 hp. The torque lead is thin at 30 lb-ft, about 2.5 percent. And the output win does not carry over to the trailer ratings: Ford still advertises a higher gooseneck maximum, per its Super Duty site. GM does say every diesel dually it builds can pull at least 30,000 pounds, with a top conventional rating of 20,000 pounds and a GCWR of up to 46,500 pounds.

It's also the first HD pickup diesel GM has created entirely on its own, from a clean sheet through to production. The block is compacted graphite iron, the crankshaft, rods, and steel pistons are forged, and a variable-geometry turbo feeds a two-stage air-to-water charge cooler. The engine is built at the DMAX plant in Brookville, Ohio, which GM expanded with $920 million in earlier investment.

The stakes are high. GM says more than 60 percent of HD buyers choose diesel, and that its brands already hold most of that business.

The changes you'll feel more than the horsepower

Until now, GM's HD trucks ran steering assist and brake boost off a shared hydraulic source. For 2027, GM splits them into two electric systems, which it says is a first for the segment on both counts.

The new rack-and-pinion electric power steering delivers about 30 percent more output than the outgoing hydraulic gear, according to GM, and keeps full assist regardless of engine speed. Dropping the pump, hoses, and fluid should also mean less to service over the life of a work truck.

The electronic brake booster pairs with bigger hardware: 14.6-inch front rotors and fixed four-piston front calipers. GM promises shorter pedal travel, a more linear feel under a heavy trailer, and diagnostics that flag brake fade or leaks sooner.

Both systems plug into the drive modes. Tow/Haul now retunes steering and brake assist alongside shift points and exhaust braking. ZR2 and AT4X models add Terrain Mode, GM's first one-pedal off-road setting for HD trucks, which brakes automatically when the driver lifts off the throttle in 4HI or 4LO.

Buyers who skip the diesel get a stronger standard 6.6-liter gas V8, now rated at 412 hp and 472 lb-ft. It uses the same Allison 10-speed transmission.

What GM hasn't said

The biggest gap is money. GM hasn't released MSRPs for the 2027 Silverado HD or Sierra HD, or what the 8.3-liter diesel will cost as an option. Fuel economy, bore and stroke, and injection pressure are also missing, as are towing ratings broken out by model. GM Authority has reported that the new engine appears in dealer order guides under the code L6P, though GM's announcement doesn't use it.

The trucks are due at U.S. dealers starting late 2026. Pricing should come first, and Ford's response on Super Duty output is the next number to watch.