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Engine Build: Sleeved And Turbocharged 6.7L Cummins Engine

Article courtesy ENGINE BUILDER.

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While most of us wish we could turn back the clock a little and make ourselves younger, McCoy Black sometimes wishes the opposite. If he was just a decade older, he wonders if he could have done some huge things in the diesel world as it was really taking shape. As it is, McCoy got involved in diesel work more than a decade ago and has built himself a solid following at MB Diesel Performance in Gold Hill, NC.

“I got into diesel about 10-12 years ago,” Black says. “If I was a little bit older and came into it 20 years ago, I feel like I could have made much more of a name for myself. By the time we got into it, most everything was already set in stone as far as big companies and stuff of that nature. We got into it from a project between me and my dad. We got together one day and started playing around with diesel trucks. One thing led to another, and we decided that we were going to build a sled truck. We built one to 800 horsepower.”

McCoy and his dad took the truck sled pulling and drag racing and decided they needed to focus on one thing, so they chose to turn it into a full sled build. However, they soon found that some of the companies they got hooked up with years ago just weren’t their best route, and it kind of left a bad taste in their mouths.

“From that day on, we started doing our own work and building our own engines and stuff of that nature and took it from there,” Black says. “A hobby turned into a job, which turned into a career. Next thing you know, we have about 50 trucks in the parking lot at all times and our schedule is about two to three months out.”

McCoy started MB Diesel Performance in 2017. The shop is 6,800 square feet and has five full-time employees. The shop can do their own cylinder head work, but utilizes Carolina Auto Machine for bigger machining jobs. MB Diesel’s main focus is Powerstroke and Cummins platforms, but that doesn’t mean they’ll turn away Duramax folks.

“Our claim to fame has been the 6.4L Powerstroke and the 5.9L and 6.7L Cummins,” he says. “That’s typically what we do the most of. Back in the day, the performance side of things is what we really pushed. With how the diesel community is lately, we’ve started doing a lot more of the repair side of things. Our goal is to have two or three different shops. We want to open up another shop in the next couple of years and do heavy-duty and big rig stuff, agriculture and stuff of that nature. And then we also want to have more of a race shop.”

For now, McCoy is happy to keep doing what he’s been doing while building plans for the future. And speaking of building for the future, the shop recently finished up a turbocharged 6.7L Cummins engine for a customer with a street truck and a grudge racing habit. However, the build started on the wrong foot.

“This engine has been a little bit of a problem child for us and for the customer,” Black says. “We took over somebody else’s build halfway through it. The build was at another shop and the customer wasn’t 100 percent satisfied, so he ended up buttoning some things up and bringing it to us.

“It was a little bit of a pain in the butt coming in behind somebody and having to wrap our head around what they were shooting for. After we got into it, there ended up being a ton more machine work than we were anticipating. It had some issues with the deck not being completely flat, but luckily we caught it. Surprisingly, the main bearings and everything clearance-wise worked out perfect, so all of the hard machine work they did take their time with and did a great job on, but somehow they rushed the rest of it. We got a head that wasn’t flat and a block that wasn’t flat, so we had to go back over some things along those lines.

“We also fought fire ring grooves for forever on it, finding the right groove in the right center diameter to be able to get a proper crush on it to where it would seal the best. We fought some head gasket issues on it here and there, but nothing too major. We eventually got it figured out.”

The customer owns a 2009 Dodge 2500 and is going for a streetable grudge truck with steel quarter panels, steel hood, steel everything with a rebuilt 6.7L Cummins.

“We ended up doing a 6.7L Cummins and sleeving it down to a 4.060˝ bore, like a 5.9L-style set up, to add a little bit of cylinder strength to it,” Black says.

The build features coated bearings, Carrillo heavy-duty rods, Industrial Injection hard parts, Dynomite Diesel Products’ 500% over injectors and two 12mm stroker pumps, ARP 625 studs, Trend pushrods, DLC-coated trunnions, billet valve bridges, and Mahle steel monotherm pistons.

“This truck still wants to be street driven,” he says. “I’m not a huge fan of the steel monotherm setups just solely because of how heavy the piston is. But it tends to live all right in the 1,800 or so horsepower range. We don’t really like to push them much past 2,000, and that was kind of the customer’s cap. If he could make 1,600 to 1,800 hp reliably, then he’s going to do just fine. That’s what we kind of shot for.”

Helping the 6.7L Cummins churn out that power is a Stainless Diesel 485, five-blade turbocharger. With this new set up ready to roll, the customer is hoping to run 5.70s-5.90s with it!

Diesel of the Week is sponsored by AMSOIL.

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