Here’s an interesting rumor that came across our desk…a new 8.3L “MegaMax” V8!
While smaller truck segments are focused on low-displacement, turbocharged gas engines, or ditching internal combustion entirely, the heavy-duty truck market is a completely different beast. Not only does each of the Big Three still offer big gas V8s — with Ford launching a Godzilla-derived 6.8-liter engine to replace the old “Boss” 6.2 — but their turbodiesel offerings churn out more power and torque every few years. In the spirit of building higher-output diesels with more torque than ever, a source with knowledge of GM’s internal powertrain development alerted us to a new, bigger, and far more potent powertrain about to emerge as the new king of the hill: a massive, 8.3-liter beast.
At least, that’s the claim: It’s important to note, of course, that this is absolutely, 100% unconfirmed by General Motors. As far as we’ve been told, if this engine is indeed well into its development cycle, we still may not hear about it for another year or two. So, we’re certainly still in rumor mill territory here, but there are several reasons why we think this does make sense, given the current truck climate and rivalry among GM, Ford, and Ram.
As for the headline specs, we’ve been told this new 8.3L diesel engine (which we are calling “MegaMax” — there’s no indication that’s the name GM has in mind for it) puts out up to 600 horsepower and up to 1,200 lb-ft of torque.
For reference, the current 6.6-liter L5P Duramax turbodiesel available in 2024 and newer Chevy Silverado and GMC Sierra HD models manages up to 470 horsepower and 975 lb-ft of torque, according to SAE J1349 power and torque certification measurements. If the automaker does see such an engine through to serial production, GM would leapfrog ahead of Ford, whose 6.7-liter Power Stroke diesel V8 cranks out 500 horsepower and 1,200 lb-ft of torque in its high-output form. Despite packing two fewer cylinders, the 6.7-liter H.O. Cummins in Ram’s heavy-duty trucks produces 420 horsepower and 1,075 lb-ft of torque.
What other specs can we expect from the large-displacement Duramax?
Even though the information we received only covered top-level numbers, you can expect an 8.3-liter option would have a major impact on GM’s HD trucks’ capabilities. Right now, Ford is out front in terms of on-paper specs, with certain models able to achieve a gooseneck towing rating of up to 40,000 pounds. That is only possible if you spec out a two-wheel drive F-450 Regular Cab with the 6.7-liter Power Stroke and the Max Tow package, to be clear, but Ford has obviously thrown down the gauntlet, so 40K is the figure to beat.
When properly equipped, the 2024 Chevrolet Silverado 3500HD/GMC Sierra 3500HD can tow a perfectly respectable 36,000 pounds. That’s still a great rating…but it’s not class-leading, and that’s the name of the game as the Big Three aim to sell as many trucks as they possibly can.
Interestingly, another strong case for a larger displacement engine centers around emissions. There’s a potential with an 8.3-liter engine to make better power and torque while still managing lower cylinder pressures and temperatures, resulting in lower overall NOx emissions thanks to having a lower compression ratio. That said, engineers obviously have to balance fuel consumption and particulate emissions among a laundry list of problems and solutions baked into fitting large-displacement engines.
As far as we’re aware, a “MegaMax” engine (not to be confused with the incontinence product, although that is a hilarious coincidence…you might need them with so much power!) will still mate up to GM’s Allison-branded 10L 1000 10-speed automatic transmission. I suspect an 8.3-liter-equipped truck may get a beefed-up variant, though Ford’s own 10R 140 version of this co-developed transmission can obviously handle the torque, to the extent that the Blue Oval puts it behind the H.O. PowerStroke today. There’s plenty of wiggle room to upgrade these transmissions in the aftermarket to handle ludicrous power outputs, so it stands to reason GM would at least take some steps to beef up the factory unit with a new, larger, and more potent engine.
When could we possibly see the 8.3L on sale?
There are a ton of unknowns here, as General Motors has yet to acknowledge this engine even exists, let alone when it may go on sale or how much it might cost. Per our source, we may see this engine actually go into GM’s heavy-duty trucks around 2026, though we obviously can’t verify that information through any official channels (even off the record) at this point.
One question mark Andre points out in the video below: What are the advantages of going with a larger displacement instead of using an electric motor for torque assist? While we obviously have to acknowledge use cases for HD trucks versus light-duty trucks, there’s feasibly room for automakers to offer some sort of hybrid solution to boost both output and efficiency. That would admittedly increase complexity, which some diesel truck owners would definitely not appreciate, especially if the sentiment around current emissions control solutions like DEF and DPF systems is any indication.
What do you think? Would you want to see General Motors put a new 8.3-liter Duramax V8 into production? Leave your thoughts below and check out the full video on TFLtruck for more of our thoughts:
