I Found the Canceled 4.5L Duramax V8 Prototypes, Then They Disappeared

The apparent owner of two prototype Duramax engines reached out to me on Facebook, only to retract their DMs. They're out there!
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4.5-liter Duramax diesel engine

Caleb Jacobs / General Motors

The Great Recession was rough on everyone in the late 2000s, especially General Motors. The automotive giant was nearly forced to dissolve, though it declared bankruptcy in 2009 and infamously accepted a bailout from the federal government that cost taxpayers $11.2 billion. GM canned multiple projects as a result, including the 4.5-liter Duramax diesel V8 meant for its half-ton Chevy Silverado and GMC Sierra. While the engine never made it to production, rumors of prototypes escaping the factory and being listed for sale deepened the lore.

When I wrote a story about these mystery engines last week, I had no idea where they were. Forums posts and empty eBay listings from years ago were the only proof they even existed in private hands. Then I found ’em. Or, rather, they found me—it’s kind of a weird story. Ultimately, it shows how wide the reach can be when you send something out onto the car internet.

Caleb Jacobs

It started last Saturday, the morning after I published my first blog about the engines. Someone sent me a message request on Facebook, and once I accepted it, I saw two photos of an engine. They didn’t introduce themselves or include any context—just the photos. I had a good idea of what I was looking at, and when I asked, they confirmed it was a 4.5-liter Duramax V8 prototype. Not only that, but they had two in their possession. Crazy!

At first, I wasn’t sure if there was more than one 4.5-liter Duramax prototype in the wild. There was an eBay listing for one in 2016, then a forum post five years later with lots of photos but no clear indicators that it was a different unit. I was stoked to learn there were more, and the owner of two had just sought me out after reading the article.

We talked back and forth over the next couple of days, and I asked the standard questions; ones like “Where’d you find those?” and “How’d you buy them?” Everything seemed normal, even after I didn’t hear back for three days. People are busy. I get it. But when I circled back to offer them anonymity, they went full ghost mode and unsent their previous messages.

Now here’s what our chat history looks like (with identifiers removed):

In more than seven years of reporting, this has only happened to me a handful of times. People stop replying, sure, but rarely do they try covering their tracks like this. It’s strange to me considering they know what I do for a living, and when I asked questions, they gave me real answers. I have to imagine they were cool with it at first, then they had second thoughts afterward.

Funny enough, they told me they wanted to sell the prototypes. They asked me to direct anyone interested in buying the engines to them. I was cool with that, and I still am because while I’ll stay true to my word of providing anonymity, I can at least DM them with serious buyers’ contact info. Price was never mentioned, but before anyone makes an offer, let me tell you what I know.

I remember most of the conversation, including the vague but still key details they provided. That includes how they got the engines and what kind of shape they’re in.

The mystery owner told me they acquired both Duramax prototypes in a bulk purchase. It looks like they buy, sell, and build engines regularly so I have no reason not to believe that. They never mentioned where the rare engines came from, or who they bought them from, but we’ll have to deal with what info we have.

They also told me neither engine was in running condition. That’s a big part of why they wanted to sell the pair, that way someone could fix and revive them for some project. It’s anyone’s guess what they need to run, which would likely be the most difficult obstacle for a new owner to get past. Sourcing components for an engine that was never actually manufactured outside a small initial batch could be impossible. I’m still not sure if either of these specific power plants was listed online before, but that forum user from 2021 mentioned the one they were selling was also incomplete.

I wish we had gotten further in our conversation before things fell off. I’d like to tell the complete story of these peculiar prototypes, like how they slipped through GM’s hands and what’s necessary to get them going again. Maybe we can revisit after they read this story and see I’m not some grimy blogger looking to expose people for clicks.

Really, I’m just a truck guy who likes talking to folks and telling stories. If you or someone you know has more info on these Duramax engines, don’t hesitate to hit me up via email, Telegram, messenger pigeon, or what have you. I’ll be around!

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