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Rumored ‘Big-Block’ Duramax Diesel Could Be 8.3L and We’re Off the Rails Now

You'd expect diesel engines to get smaller as time goes on, but recent reports claim GM's truck power plant could grow by more than a liter.
Caleb Jacobs

I wasn’t going to write this. I’ve refrained ever since I saw the rumor emerge about a week ago. But now that people are still talking about the so-called “big-block” Duramax, I feel like it’s time to acknowledge the possibility, however scant, that we might get a new diesel pickup engine with 8.3 liters of displacement.

TFL Truck posted a story on Jan. 30 about the rumored next-generation diesel V8, citing “a source with knowledge of GM’s internal powertrain development.” General Motors hasn’t confirmed that the Duramax will grow in size, but TFL‘s source says it could be an 8.3-liter lump making as much as 600 horsepower and more than 1,200 pound-feet of torque. The power numbers are believable—Ford is making 500 hp and 1,200 lb-ft with its high-output 6.7-liter Power Stroke—but I’m not so sure about the size of the engine.

Others in the industry feel the same way. The topic was discussed on this week’s episode of The Truck Show Podcast, which is co-hosted by Banks Power brand manager Jay Tilles. If you didn’t know, Banks is a supplier of Duramax-based engines to the US Army for its Joint Light Tactical Vehicle program, so they also have a special interest in this particular diesel power plant. While he remained tight-lipped for the most part, Tilles provided a smidge of insight.

“So we’ve heard differently inside the halls… We’ve heard it will be a little smaller,” he said. ” I can’t say what we’re hearing; we’ve heard that it’s not 8.3 [liters].”

When asked by co-host Sean Holman if it was above or below 8.3 liters, Tilles replied, “below.” He added that the number is more “reasonable,” perhaps in line with past GM big blocks. That could mean 7.4 liters, which is the metric displacement measurement of GM’s 454-cubic-inch gas V8s from yesteryear. If that ends up being the case, it would be the largest engine in the heavy-duty pickup segment—gas or diesel—beating Ford’s 7.3-liter Godzilla by a hair.

The 2024 Chevy Silverado HD’s 6.6-liter Duramax V8. Caleb Jacobs

Now, there are a few reasons that bigger displacement would actually make sense for the upcoming Duramax—and believe it or not, improved emissions is one of ’em. While you and I both know that larger engines can make more power more easily, they also don’t require such high cylinder pressures to produce monstrous output. That means lower NOx emissions, which means happier EPA enforcement agents.

Ford, GM, and Cummins are nearing the limit of what’s possible in terms of performance with their current engine displacements. Ford and Cummins’ diesel pickup power plants are 6.7 liters while GM’s Duramax is and always has been 6.6 liters. Increasing engine size may be the most logical next step, especially if manufacturers deem that hybrid truck powertrains aren’t ready for a full-scale rollout just yet.

In short, I believe that a bigger Duramax may be on the way, even though GM hasn’t confirmed it. I doubt it’ll be 8.3 liters, but hey—it’s a flashy figure. People are bound to be drawn in by it. We’re likely at least a couple of years away from seeing it reach production, so in the meantime, I’ll be on the lookout for any and all secret documents I can find revealing more info about the big-block diesel.

Man, that just feels good to type.

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