GM's new V8 diesel is torquier than a Chiron

8.3-litres, more than 500hp, and 17 tonnes of towing capacity - truck yeah mothertruckers

By Matt Bird / Friday, 25 September 2026 / Loading comments

You wouldn’t be alone in considering the United States of America like another planet sometimes. Everything seems so different that it can be hard to believe that it’s only an ocean away. And nowhere does the US seem more opposed to Europe than when it comes to diesels; over here it’s been almost ostracised in the race to electrify, while over there - with big distances to travel and big loads to haul - the oil burner still reigns supreme.

Hence General Motors' all-new diesel engine, an 8.3-litre Duramax affectionately nicknamed the Mongoose. The numbers, predictably, are outrageous: 555hp, 1,230lb ft (!), and many tonnes of towing capacity, with nine straight out of the box and up to 17 with a gooseneck attachment. So a Duramax can tow your race car. Or 10.

Unsurprisingly, GM claims that the Mongoose, coming to the Chevy Silverado and GMC Sierra, offers best-in-class power and torque. This is no mere evolution, either, but rather a ‘clean-sheet HD V8 designed, developed and manufactured in-house for heavy-duty pickup applications.’ In case there was any doubt about the demand that exists Stateside for absolutely enormous trucks, GM has deemed it sufficient to create an all-new diesel of more than 500 cubic inches.

But there’s more to Mongoose than simply an ain’t-no-replacement mindset: the new 8.3 gets a fully forged crank and compacted graphite iron block for strength, a variable geometry turbo, an ‘advanced’ combustion system and high-flow fuel injection. Everything has been designed with heavy-duty use in mind, from launching weighty trailers to slowing them back down again; last thing you want with your speedboat on the back of the truck is any uncertainty.

The transmission, a new 10-speed auto, has been designed with that logic in mind as well: ‘smoother acceleration, stronger grade performance and more confident control’ when towing are promised. It’s the same gearbox that’s hooked up to the 6.6-litre petrol V8 also offered. But then that must make do with a puny 412hp and 472lb ft, despite a new intake manifold. Wonder which Silverado offers better gas mileage?

While it’s the diesel that will hog the headlines, it isn’t just the torque to reel in space stations that marks out the MY27 Silverado and Sierra. Electric power steering is now fitted, again designed with robust use in mind: EPAS is easier to maintain than a hydraulic setup, offers more assistance for easier maneuvering, and is assembled from sturdier hardware ‘for harsh truck environments.’ Granular feedback matters rather less than dependability when it comes to hauling, after all. GM says the new setup will help those behind the wheel ‘feel more connected, more in control and more confident behind the wheel.’

That confidence will be helped further by a new electronic brake booster, maintaining a consistent pedal feel in all conditions. Again the purists won’t like it, but it eliminates the failure points of a hydraulic system once more, offers better diagnostics and can help with assistance like adaptive cruise. Probably quite handy when there are entire states to cross. If it makes the big trucks easier with which to move big stuff, GM’s going to do it, now including new drive modes (Normal, Tow/Haul, Off-Road and Terrain) plus features like Transparent Trailer View, Trailer Side Blind Zone Alert and Automatic Emergency Braking. The latter can seem like overkill in a Mini - it’s probably quite useful here.

“For 2027, we took GM’s proven HD validation playbook and turned up the capability — integrating new powertrain, braking, steering and chassis technologies for serious customers who push their trucks hard every day,” said Mark Dickens, whose tremendous job title is Executive Chief Engineer for GM Full Size Trucks and SUVs. “HD customers don’t hold back — and neither did we.” Hell yeah. US customers can expect the new trucks in showrooms before the year is out; those over here must of course rely on importers to enable their American dream. But if a Silverado Trailboss can make it here, surely an 8.3 diesel can as well…