Compound Turbo 6.6L LB7 Duramax Engine - Engine Builder Magazine
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Diesel of the Week

Compound Turbo 6.6L LB7 Duramax Engine

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Mike Maas is a jack of all trades kind of guy. Like most people in the automotive repair and performance industry, he got his start fixing up his friends’ rides. That slowly, but surely, led to him growing a customer base in his community that he eventually leveraged into a business.

Five years ago, Maas started up Dark Horse Diesel LLC in the small town of Watkins, MN. With a population of only 935 people in Watkins, Dark Horse Diesel’s one-man-operation is the perfect size to get the job done and provide for all diesel needs in the area.

2003 Chevy Silverado

Maas has a single hoist in his 28’x60’ shop and mainly focuses on repair, performance and tuning work on Chevrolet and Dodge trucks. Dark Horse Diesel also specializes in Duramax engines and Allison transmission work.

For machining work, Maas goes to Craig Brutger of Craig’s Machine and Dyno, who he says is the best in the state of Minnesota. For this Diesel of the Week, we’re featuring Maas’ 2003 Chevy Silverado that he decked out with a fully built 6.6L Duramax LB7 engine.

LB7 Duramax

“It was just a typical shop truck when I got it,” Maas says. “It was a toy we ran around in and messed around with from time to time. It kept progressing overtime and went through a lot of changes before it got to where it is now.”

To his word, Maas still uses the truck for just about everything as his daily driver. He decided on a regular cab truck amid a sea of three and four-door trucks because of his love for the LB7. In fact, he’s owned seven LB7 trucks over the years, all of which he’s been impressed by.

This Silverado went through a gradual evolution over the years, from a mild shop truck to a souped-up powerhouse. The earlier build consisted of a stock LB7 bore block with a balanced stock crank, Carrillo connecting rods, MAHLE Motorsports cast de-bowled pistons with valve reliefs and 16.1:1 compression ratio.

For the camshaft, Maas enlisted the help of Craig’s Machine and Dyno to make a custom firing order camshaft that moves the valves in a pair of Wagler Competition street cylinder heads. The engine also featured a compound turbo setup consisting of a BorgWarner S485 atmospheric turbo and a BorgWarner S369SXE valley-mounted turbo, which was tied together by HSP Diesel.

These parts, along with some other custom additions and EFI tuning by Danville Performance, brought this early build to a peak of 1,244 hp and 2,193 lb.-ft. of torque. Maas took the truck down to Scheid Diesel for the dyno competition and ended up winning two years in a row.

In the time since this build was finished in 2017, Maas has made some notable changes to add 300+ horsepower to the Duramax.

“We dyno’d the thing to over 1,500 hp, but didn’t really go farther than that,” Maas says. “There was a good amount of fuel left and if I had to guess, I think it could have hit 2,000 hp if we kept going.”

The new motor that Maas refreshed and built this year is another LB7 in terms of the heads, injectors, etc., but this time he opted to use an LML block.

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The engine has a Callies Ultra billet crankshaft and CP forged pistons. A Callies hybrid kit was also installed. The bottom of the engine is all billet, with a billet SoCal stud girdle, SoCal mains, and an ATS flywheel. Up top, the Duramax now features a set of Kill Devil Diesel cylinder heads.

Maas also opted to change the compound turbo setup for some added power. HSP Diesel handled the turbo setup again, installing a BorgWarner S476 in the valley with a 12mm S&S pump and a Garret 102mm GT55 on top with a 10mm S&S pump on the belt. S&S 300% over injectors provide the fuel and round out this awesome setup.

“It’s all just really reliable,” Maas says. “I haven’t really had any problems with it yet and I hope it stays that way.”

While Maas’ Silverado may look like an unassuming shop truck on the outside, it’s sure to make onlookers double-take as it flies down the drag strip.

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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