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The “Baby Duramax” Was A Diesel V8 That Was Set To Exist Beneath The 6.6L We See Today

2010 Chevrolet Silverado 1500

The Great Recession in the late 2000s was rough on everyone, especially General Motors, which if you forgot, declared bankruptcy in 2009 and accepted an $11.2 billion USD bailout ($16.8 billion in 2024 stimulus bucks) from the federal government. And whether it’s been explicitly outlined or not, this event saw a lot of hand holding from the Obama administration, leading to the questionable yet oh-so-politically correct business decisions we’ve observed, such as the winding down of both Pontiac and Hummer, while positioning the Chevrolet Sonic (a stylish yet placid subcompact that existed for compliance purposes that made no money for the company) to be built at the GM Orion plant in Michigan instead of Korea. Surely a cash-negative decision.

Some things also never made it to the light of day. GM had to scrap several projects, and several would have been fantastic. On one end there were several new incarnations coming from Hummer, which would have gone right after the mid-sized Jeep Wrangler and Toyota 4Runner instead of another behemoth SUV. Then there was the Pontiac G8 wagon and ute, which would have come directly from Australia with the existing G8 sedan. Let’s not get started on the mid-engined Cadillac, or the V16 engine luxury sedan that was in development, either, or the original plans of the Escalade-V.

Speaking of engines, another stillborn project was the much-rumored, much-anticipated 4.5-liter Duramax diesel V8 engine designed for the Chevrolet Silverado and GMC Sierra 1500 pickup trucks. To the dismay of many GM faithful, that engine never made it to production. However, prototypes did escape the factory and still exist.

Ah, all of this stuff is at least 15 years old at this point, and older. Maybe pre-bankruptcy GM was a more fun GM? Certainly, Bob Lutz made things interesting, at least. Old habits die hard, too, as the corporate Fun Police have canceled projects like the original plans for the seventh-generation Camaro, a sixth-gen Z/28, a 6.6L “LT3” V8 that would have gone in said Z/28, a midsize GMC SUV based on the rugged Canyon pickup truck, and so forth. All in the name of E-for-Electricity! electric vehicles. Which has been the biggest money pit for the automaker that we’ve ever seen. Maybe its Cruise autonomous vehicle venture topped that, but playing Tesla reindeer games in the pursuit of “unlocking shareholder value” (doubling as regulatory compliance-driven marching orders) certainly hasn’t gone well for The General, who has always lived and died by its V8 engines, body-on-frame vehicles, and a proud flyover state customer base. All of which is certainly at odds with the gatekeepers within the marketing and PR departments.

4.5L Duramax (LMK) Engine Prototypes: Details

Anyway! The Drive recently wrote a story regarding these mystery engines and the rumors that they were still out there, lurking within the garages of individuals, and if, by fate, one person reached out to prove that the 4.5L Duramax Engines do exist, or at the very least, 2 of them do. In a series of messages between writer Caleb Jacobs and a mysterious individual, two images of what would have been the first diesel engine to return to half-ton trucks since 1998 confirmed that some prototypes are out there; not only that, but the individual mentioned wanting to sell the prototypes, which we should add, apparently need some TLC to get running.

4.5L Duramax LMK

If you didn’t know, the 4.5L Duramax Engine also carried the code name LMK, was first announced in 2008 and was destined to be the powerhouse for GM’s half-ton pickups. This engine was very different from the Duramax engines we have today, with more significant displacement and more cylinders arranged in a V. Featuring reverse-flow heads, a 72-degree bank angle, and a lightweight compacted graphite iron block. Reports say the engine was capable of 310 horsepower and 510 lb-ft of torque, which were very impressive figures for the era.

Today, the spirit of the original 4.5L Baby Duramax diesel exists in the form of the LZ0 3.0L Duramax, which is a buttery-smooth straight-six diesel that makes 305 HP and 495 lb-ft of torque. And you can get it in everything right now from a Chevrolet Silverado 1500 to a Cadillac Escalade, if you really want one.

2010 Chevrolet Silverado 1500

Written by Zac Quinn

Zac's love for cars started at a young age, after seeing the popular Eleanor from Gone In 60 Seconds. From there, fascination and enthusiasm blossomed and to this day the Ford Mustang remains a favorite. His first job started out detailing cars, but also provided the opportunity to work on restoration including an 1968 Ford Mustang, Pontiac Firebird, and a C3 Corvette, though he left that job before further work and experience could be had. From there, he was a detailer at a car dealership before quitting that job to try and finish college.

Much of his free time while studying was spent watching YouTube videos regarding new cars, or off-roading. 4WD247 is a personal favorite channel which rekindled a dying flame in car enthusiasm, now tailored towards trucks and SUVs and the fun that can be had building up an overlanding rig, and going on adventures, though, that chapter remains unwritten for the time being.

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