Over a decade ago, General Motors developed an engine that could have revolutionized the market for half-ton trucks and diesels. Tragically, it never did. The 4.5-liter Duramax V8 that was supposed to power the half-ton Chevy Silverado, GMC Sierra, and Hummer H2 fell victim to GM’s late-2000s bankruptcy and was canceled before it reached production. Whether it was an unavoidable cut or a ploy to secure GM’s much-maligned government bailout, the decision was reached to keep it out of the people’s hands. Mostly.
But some prototypes escaped the factory. After we published our first story about it last summer, I received a mysterious email from a man in Sweden who claimed to have one. After a months-long plunge down the rabbit hole of the engine’s lost history and demise, and an interview with diesel tuning legend Gale Banks, who saw it up close in 2006 before it got canned, we can confirm that it’s real. An unused 4.5L Duramax V8 prototype did indeed make it into private hands. In Sweden. This is the story of how it all happened.
The light-duty diesel, engine code LMK, was almost ready to deploy before the Great Recession hit in 2008. Its existence has haunted the metaphorical halls ever since, briefly resurfacing at unexpected times and in unexpected places, always without an explanation. The last time I got close to finding one, its owner agreed to talk, then mysteriously retracted his messages and went dark on me. Not long after, Henrik Bengtsson reached out to me with an enticing opening line: “I got one.”
Bengtsson and I emailed, texted, and talked over the phone about the diesel V8 he practically stumbled upon years ago. The tale of how he came to own it all the way across the Atlantic is amazing; hearing it was totally worth the $66 international call fee. And on top of that, he sent me a folder full of original photos showing the engine’s innovative features that still stand out today.
From there, I hit up Gale Banks, the turbocharging guru and diesel-tuning godfather. When I went searching for more info about the 4.5-liter Duramax, he was the first person who came to mind. Wouldn’t you know it, he had all the answers I was looking for and more. His recollection of the project is near-encyclopedic, and the anecdotes he shared are gold (as always).
Not every detail here is new, though many are, and it’s my goal to make this the centralized place for all info related to the LMK. But rather than turning this into some boring data dump, I want to guide you along the same path I went down to get where we are now.
So, let’s start with a history lesson.
The 4.5L Duramax Origin Story
From inception, the LMK was set to power vehicles built on GM’s half-ton truck platform at the turn of the last decade. Gary Arvan was the chief engineer for GM Duramax diesel engines when the 4.5-liter project started taking shape in 2005, and Charlie Freese was the executive director of GM’s diesel powertrain engineering right alongside him. The duo was tasked with developing a small-block alternative that made more torque and got better fuel economy than its gas counterpart, all while meeting the increasingly tough emissions requirements.
“In today’s auto industry, you can’t afford to develop an average anything,” Freese explained to Automotive News back in ’07. “You can’t set your goals that you want to be like everybody else.”
That quote alone explains a lot about the LMK Duramax. See, it had a laundry list of features that were not only interesting but also genuinely innovative for its time. Chief among its intriguing hardware is the hot-vee turbo layout, which inverted the flow of exhaust gases compared to traditional diesel engines that send the spent air outwards. The variable-vane turbo sat between the cylinder banks where it accelerated the air coming in, force-feeding the engine with boost more quickly since it has minimal distance to travel. It’s a tactic replicated in high-performance cars like the Mercedes-AMG GT and GM’s own short-lived CT6-V with the fabled twin-turbo, 4.2-liter Blackwing V8. The LMK did it before either of them.
The auto giant unveiled the powertrain to the public in 2007 and even dropped it into a Suburban HD Z71 concept for the following year’s SEMA show before pulling the plug. This disappointed everyone who wanted to see the engine that Car and Driver called “revolutionary” at the time. What’s more, it was a big blow to the folks at GM who worked hard on the project for years. But over time, the LMK has more or less faded from the public conscience.
Ahead of Its Time—Before Its Time Ran Out
Truly, the 4.5-liter was impressive. That’s what Gale Banks recalled as he talked me through the handwritten notes he made while previewing the prototype LMK in 2006. “You know, it’s a victim of timing and circumstance rather than a failure of engineering,” he insisted. “I want to point that out.”
GM brought Banks in so that his company, Banks Power, could “represent the Duramax to small OEMs, like in the marine industry.” His experience with marine power systems goes back decades, even before he started building twin-turbo, big-block Chevy V8s for the United States Navy in the mid-1970s. They later switched to diesel, which no one has more experience with than Banks in terms of performance. Given his ties in the marine and military industries, GM found it prudent to let him in on the engine’s secrets before revealing them to the public.
During our call, Banks harped on the hot-vee for a minute, commending Freese and Arvan for going that route when no one else was. “If you look at how the air enters the Ford 6.7-liter [Power Stroke diesel], it flows through the valve covers and then into the intake ports that are cast on the outside of the head,” Banks recalls. He served as a subject matter expert for Ford on that engine. “Well, so does [the LMK], only it was years earlier. So these guys were way ahead of it.”
“Doing this innovation with the hot-vee eliminated so many parts,” he continued. “It eliminated about two dozen parts which, at their cost level, that was 100 bucks per engine.” For what it’s worth, I found conflicting reports saying it was more like $600 in savings per engine by going with the hot-vee. Either way, it was an undoubted benefit. “So not only was it compact, but it was less expensive. And it improves the thermal efficiency, at least on the exhaust side.”
Banks then noted the common rail fuel system, which ran at 29,000 psi. “That’s respectable even now,” he quipped. It could also manage multiple injections per combustion event, reducing noise and improving emissions. To that point, the team incorporated diesel exhaust fluid—boo, I know—and selective catalytic reduction. This was advanced stuff in the mid-2000s regardless of your feelings toward the emissions equipment.
Other interesting tidbits included a block made of compacted graphite iron and split-cap main bearings. You read that right—split-cap main bearings. “How the hell do you even do that?” Banks laughed. “Breaking the cap off the [connecting] rod, I get that, but mains? Pretty cool. Anyhow.” When you’ve blown this guy away, you’ve done something special.
What Happened After It All Fell Down
All this goes to show that GM was on the verge of potentially changing the half-ton truck category before canceling the LMK. It was designed to fit anywhere a small-block Chevy would, and at that time, no light-duty pickup had offered a diesel engine option since the GMT400s with the 6.5-liter Detroit in the 1990s. It had all the right ingredients to become a hit.
Who knows how differently the segment would have looked if GM followed through with the LMK?
Indeed, no other light-duty diesel came along for years until Ram introduced the EcoDiesel 1500 in 2014. That prompted GM to bring a 3.0-liter Duramax inline-six to market in 2019, with Ford following suit by selling the F-150 with a 3.0-liter Power Stroke V6 for a short time. Of those, only the GM Duramax I6 remains.
It’s a pretty big hit, too, as GM offers the 3.0-liter diesel across several makes and models. The Chevy Silverado and GMC Sierra 1500 can be optioned with it, as can the Tahoe, Suburban, and Yukon SUVs, plus the Cadillac Escalade. While vastly different in form than the 4.5-liter LMK, it essentially fills the same role as a gas V8 alternative that makes more torque and provides better fuel economy.
In the years since GM officially called it quits with the 4.5-liter Duramax, it has mostly drifted into obscurity. There was some chatter in the mid-2010s that it could be making a comeback, though most of that seems to point to a MotorTrend article with this puzzling line: “GM remains optimistic that the Duramax 4.5L V8 diesel may be a viable option in its future portfolio.” Clearly, that never panned out.
Survivors Still Exist, Even Across the World
What’s maybe most interesting is that some examples of the LMK engine have popped up in the wild. You can find old eBay listings and forum posts with random individuals claiming to own one, which I wrote about in June of last year. After that, someone reached out to me saying they had several prototypes in their shop, only to unsend their messages in hopes of erasing the paper trail. Just super odd.
This is where my new pal Henrik comes in.
Having read my past blogs about the 4.5-liter Duramax, he reached out with an offer that was too tempting to resist:
Not only was he willing to share more info about the LMK and how he got it clear across the ocean, but Mr. Bengtsson was also down to send pictures—original ones that have never been published anywhere until now. I took him up on his offer, and what followed was weeks of back-and-forth email correspondence to learn more about the Duramax that never was.
Bengtsson is the one who really kickstarted this process for me. I thought I was more or less finished writing about the 4.5-liter, but once he told me his story, I knew I needed to pursue something like this. My curiosity was piqued once he mentioned where he bought the engine from.
“In Sweden, we have a website called Blocket. It’s a little bit like your eBay, you can say,” Bengtsson explained. “And there was a guy, he was selling this kind of turbo.”
See, Bengtsson likes turbos. He has a lot of them—big ones—and he puts them on everything, like Mercedes diesels. As he explains it, he was only looking to buy a turbo from the seller on Blocket but they ended up cutting him a package deal that included the LMK.
“He was one of the guys that was in a company,” Bengtsson continued. “I don’t really understand exactly how it was, but the company itself went out of business. And they used to buy a lot of GM engines for certification for boat engines in Sweden.”
Once he spotted the Duramax’s hot-vee construction, he was intrigued. He recognized the layout as he’d seen it on some gas Mercedes engines, like the one I mentioned in the AMG GT, but never in a diesel. He bought it with hopes of learning more, though when he reached out to GM, they weren’t much help. Bengtsson forwarded his correspondence with GM customer service to me, in which they effectively shut him down. Translated from Swedish, the company rep said:
“All prototypes of this engine were scrapped but at least one engine has since appeared on the market for unknown reasons. GM does not provide any support, technical information or spare parts for the 4.5L LMK as this engine has never been officially released on the market.
“Since we unfortunately will not be able to help you further with your case, it will be closed in connection with this response.”
In fewer words, they shut him down. I also reached out to GM’s American media team for this story but ultimately never heard back. Still, Bengtsson was intrigued to learn that the LMK he owned was one of the few that escaped the crusher. He tells me he also raised an eyebrow when reading my previous blog about the engine where I said it was so rare to find. “I have an unused one,” he laughed.
That’s when he got in touch with me. A week or two of emailing led to him sending this big batch of photos that I’ve attached here for you to ogle at:
This thing is a total peach. You can see the hot-vee turbo, a BorgWarner, from several different angles, as well as the CGI block. It doesn’t even have any soot in the turbine housing, showing it’s as fresh as a loaf of homemade bread. I sent these photos to Banks and he was pleasantly surprised to find it in this condition.
“Generally, the prototype trucks would have been crushed, and the engines along with them,” Banks told me. “Trucks get crushed. Engines get leaked.”
How Many Others?
Apparently, the guy Bengtsson bought the LMK from said people in the States were running them in road cars. I still haven’t found any examples of that, except for one that Banks told me about. According to him, there was somebody who put a 4.5-liter Duramax in a regular vehicle, and his name was Bob Lutz. Maybe you’ve heard of him?
Lutz helped lead each of Detroit’s Big Three brands at one time or another, and he was with GM from 2001 to 2010. Most gearheads know him as a true enthusiast executive who helped bring back the Chevy Camaro. “He was vice chairman of General Motors at the time,” Banks told me. “He had one put in a Buick Rainier and had it at the Milford Proving Grounds.”
Y’know, one of these:
This tells me that the people at GM were having a ton of fun with the 4.5-liter Duramax. There’s no telling how many others were built, but you can bet there were more than a few lying around at one point.
“Well, when you’re that close to production, there’s a lot of prototype or pre-production engines put into vehicles,” Banks continued. “You’re proving it at Milford and other places. Do your high-altitude work, do your cold start work. There are different places they would go with those trucks. And then the trucks, it’s just a pickup truck. From the outside, you can’t just tell that it’s a diesel unless you pick up the noise or the odor a little bit.”
I’d say that explains how so many made it into private hands, though it’s impossible to say how many still exist.
Reflecting on What Wasn’t
Is the world a worse place without the 4.5-liter Duramax in it? I’m not sure. Probably not. But I’m blown away by how much work was put into the project, only to cancel it at the last minute. I understand that happens sometimes in the auto industry, though thankfully, some of the folks directly involved with the LMK are still around to tell the tales.
I hope I’ve done a good job of relaying these tales to you in a way that will exist for quite some time. Stories like this are why I love my gig. And if it weren’t for folks like Henrik Bengtsson and Gale Banks, I’d be none the wiser about the time GM nearly broke the half-ton pickup truck category wide open.
Just imagine what could have happened under different circumstances. If GM never went under, could the LMK Duramax have pushed Silverado sales past the F-150? How would Ford have responded? What about Ram? I like to think it would have been a mad rush to develop a light-duty diesel of their own in response. Instead, things stayed largely the same for another decade as gas V8s remained king in the half-ton truck segment.
Again, I’m not sure that’s a bad thing, but I would love to have seen some tuned-up LMK-powered Silverados running around. I’m sure the people at GM would’ve enjoyed that, too. C’est la vie.
Got a tip or question for the author? Contact them directly: caleb@thedrive.com
www.thedrive.com
#GMs #Lost #Duramax #Prototype #Couldve #Reinvented #Modern #Trucks
