First-of-its-Kind Compound-Turbo L5P Duramax Engine - Engine Builder Magazine

First-of-its-Kind Compound-Turbo L5P Duramax Engine

While incredibly rewarding, nothing about this L5P Duramax build was easy for Lead Foot Diesel Performance – everything was custom or a first. From the billet crank to the one-off compound turbos, this L5P Duramax is impressive. Check it out!

Diesel of the Week is presented by

Some people are just built to modify stuff; it’s in their DNA. Vinny Himes knew from a very young age that he was one of those people.

“I grew up with my grandfather’s entire salvage yard at my fingertips,” says the sales manager at Lead Foot Diesel Performance (LFDP), a 32,000-square-foot shop in Monroe, GA, with 22 drive-in bays and 18 employees on site. “I had a fully modified riding lawn mower that would do wheelies across the yard when I was 8 years old.”

Duramax truck
Bobby Jacobs had one overarching goal for the Lead Foot Diesel Performance team charged with resurrecting his L5P: the bigger, the better.

Bobby Jacobs, the owner of Florida-based Secure Fence and Rail LLC, is cut from a similar cloth. His own diesel addiction started with a 2016 LML Duramax that he bought already semi-built from the previous owner.

“Just like me, he couldn’t leave well enough alone,” Himes recalls. “He used the truck for hauling his materials around to various job sites, [where he was] building fences all over the state of Florida. With each bolt-on upgrade, the truck made more and more power.”

In true “Florida Man” fashion (Himes’ words), Jacobs worked his truck to a point where, eventually, the engine gave out. Rather than rebuild it, he wanted to upgrade to a brand-new Denali. This was happening just as the COVID-19 pandemic was taking hold, and new vehicles were scarce.

L5P Duramax engine
With the cylinder heads bolted back into place, the engine started to take shape, along with a pop of color from the painter.

After searching high and low, Jacobs finally found the truck he wanted – a 2020 GMC Denali. It was the only one available in the state of Florida at the time, so he quickly snatched it up and set about making it unmistakably his – custom wrap, top-of-the-line sound system, lighting upgrades, etc. A “spared no expense” suspension lift, along with custom wheels and tires, finished off the package. Now, it just needed the performance to match those good looks.        

The L5P was a relatively new platform, especially back then. While it was similar to the previous 6.6L Duramax, the 2020 version had some distinctions from earlier 2017-2019 models, particularly in the rotating assembly, fuel system, and turbocharger.

“This means performance parts are limited…there’s very little support for it,” Himes says. Even with all the available bolt-ons, this L5P was nowhere near the power of Jacobs’ previous LML. Still, new parts were added on as they became available. This included a modified drop-in turbo replacement with a much larger compressor wheel that claimed to produce around 680 horsepower with supporting modifications.

billet crankshaft
Mocking up the rotating assembly, LFDP learned the main bearings and rod bearings needed to be chamfered. LFDP’s neighors, Jon Kaase Racing Engines, got them custom chamfered bearings, so everything spun freely. 

But, during an early test drive with the new turbo, something went very wrong. “There was a ‘pop,’ and then the white smoke started billowing out of the tailpipe,” Himes says. “The truck coasted over to the shoulder after successfully whiting out all four lanes of traffic.”

After towing it back to the shop, they discovered that the turbo shaft had failed and spit the turbine wheel down into the exhaust. Unfortunately, the turbo’s failure meant just about every drop of engine oil had poured out, causing major internal engine damage.

Jacobs was referred to Lead Foot Diesel by some acquaintances in Florida who had witnessed the turbo failure. After loading up his truck and hauling it north to Georgia, Jacobs met with Charlie, the shop’s Duramax specialist, to discuss his goal for the rebuild. It was simple enough – the bigger, the better. The LFDP team got to work sourcing all the parts they’d need to make this the baddest and, as they would eventually learn, the rarest L5P in the country.

L5P Duramax engine
The Fluidampr and one-piece Socal Diesel billet flexplate wentto Jon Kaase Racing Engines to ensure the entire rotating assembly was balanced together.

“SoCal Diesel knows the underlying cause of the infamous Duramax crankshaft failure is the firing order of the engine,” Himes says. “They provided us with their signature Alternative Firing Order Duramax Camshaft to ensure this project wouldn’t come back with a broken crank. We took it a step further and ordered a billet Bryant crankshaft. At the time this was all taking place, nobody in the industry offered modified pistons for the L5P engine, so we purchased a set of factory replacement Mahle pistons and sent them to Industrial Injection in Salt Lake City, UT. Tyler Kipp was the contact there, and he got our pistons de-lipped and fly cut, and had the piston tops coated with a thermal barrier coating while the skirts got a ceramic coating.”

What the Lead Foot team didn’t know at the time was that Jacobs would be the first person in the country to have a privately owned billet Bryant crankshaft in an L5P.

“We found out very quickly that being the first in this area was going to add a lot of time to the project,” Himes notes. “Once the billet crankshaft was shipped to us, we then had to ship it to Wagler Competition Products to have a custom set of billet rods made to fit the narrower rod journals.”

transmission and engine
With the engine completely back together, it was mated to the King Kong 10L transmission from Randy’s Transmissions, along with the completely one-off custom compound turbos that were never intended to fit this platform.

Once the completed rotating assembly came back, Lead Foot’s in-house engine builder got to work putting the powerplant together. They soon enlisted the aid of a neighbor – the legendary Jon Kaase Racing Engines – to ensure the crank was set up properly.

“They were a huge help, as they deal with these crankshafts daily and this was our first experience with one,” Himes says, adding that the Kaase team provided a custom one-off set of chamfered main bearings and rod bearings. “Knowing this bottom end had their expertise and seal of approval guiding it back together, really made us feel good about the reliability we are giving Bobby!”

Elsewhere, a generous helping of ARP fasteners were used throughout the build to ensure all components stayed securely in place. “The extra insurance of using good quality fasteners was never an option,” Himes notes, “as we knew we were going to be the first shop installing compound turbos on a 2020+ Duramax.”

compound-turbo L5P Duramax engine
The L5P’s beautiful red and black engine scheme quickly disappeared as the engine accessories and wiring harnesses found their way back home.

Speaking of which, the valley turbo is stock for the time being, Himes says, while the secondary turbo is a BorgWarner S480.

“Nobody to this date makes a piping kit for the 2020+,” he adds, “so we ordered a kit for a 2017-‘19 L5P, and our in-house fabricator made the necessary adjustments to ensure a perfect fit on the newer-style engine.”

The fuel they needed to match the extra air was provided by the 12mm CP3 conversion, which pumps that extra fuel through a set of S&S Diesel Motorsport 25% over injectors.

Duramax truck
After a groundbreaking makeover, Bobby Jacobs’ first-of-its-kind L5P awaits the trip back home to Florida.

While incredibly rewarding, nothing about the project was easy, according to Himes. “Everything was custom or a first, and that means we used more patience than assembly lube,” Himes says. “Bobby was extremely patient while waiting for all these nonexistent parts to come to fruition. Plus, Jon Kaase Racing Engines is a world-renowned engine building company, and the fact that they not only gave us the time of day, but went above and beyond to ensure we had everything put together correctly was a huge blessing.”

The truck has since completed multiple test drives successfully. As of this writing in mid-March, Jacobs was on the way up to Lead Foot to drive his first-of-its-kind L5P back home to Florida, where it’s likely to turn more than a few heads.

Diesel of the Week is sponsored by AMSOIL. If you have an engine you’d like to highlight in this series, please email Engine Builder Editor Greg Jones at [email protected].

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