376 cid LS3 LSR Engine
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Engine of the Week

376 cid LS3 LSR Engine

When a customer came to Mullenix Racing Engines wanting to kick it up a level from his stock bottom end and stock heads, engine builder James Mullenix built him a 376 cid LS3 LSR engine. Find out what went into this LS build and what kind of power it’s cranking out!


For 20 years, James Mullenix has been synonymous with extreme horsepower applications including classics, muscle cars, high performance street, race cars, boats, and off-road racing. When customers are looking for that next level of power, they call James, and for good reason too.

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James loves high-horsepower performance and has set his focus on late-model LS performance engines. Whether you’re looking for 2,000 hp+ race applications, or a 500 hp street application, Mullenix can build an engine for you. After all, he’s been in the business literally since he was born.

“I was pretty much born into it,” Mullenix says. “My grandfather used to race boats and dragsters and all that kind of stuff back in the ‘50s. My family carried it on and now I’m the next generation. We were all born into the racing stuff. I’ve been doing engine work since I was 12 years old.”

James learned a lot from working with his family, however, right out of high school he went to work for car dealerships to become a better technician.

“I went through all the training courses and classes they have for automotive technology, electronics and mechanical,” he says. “I worked for Toyota for several years and got master certified. Then I got my master ASE certifications. Then I went to the American market and went to the Chevy dealer and got my master GM technician certification. From there, I worked for a shop called A&A Corvette for about eight years where we built late-model performance Corvettes – C5s and C6s. From there, I went and did my own thing with Mullenix Racing Engines.”

Mullenix Racing Engines used to be located in Simi Valley, CA until just a month ago when James made the move to New Braunfels, TX. While he gets his new shop in order, he will be continuing to partner with JCG Restoration.

I’ve been building motors for him for about 11 years for all the cars they race in autocross, road racing, Optima series and all that,” Mullenix says. “I’ve been building all the motors for his shop and customers he has, so it worked out to go and start working for him for until I get Mullenix Racing Engines established out here again.”

Before Mullenix Racing Engines left the golden state, he completed a build of a 376 cid LS3 LSR engine, and like any of his builds, Mullenix was focused on delivering a quality engine using parts he believes in.

“I had a customer come in with a Camaro,” he says. “I had worked with this customer in the past. He had a stock bottom end, stock heads, and we did a cam and blower only. I helped him convert the car to e85 a year ago or so. We started going up from there and he wanted to get crazier with it. He wanted to build a stock displacement motor that was able to withstand the abuse we were going to put it through.”

The build started with a new, Concept Performance LSR, eight-bolt main block, and the machine work was sent to Unleashed Custom Machining in CA to get the 376 cid block in proper order.

“We kept it at a 376 cubic inch motor,” Mullenix says. “It was a 3.625˝ stroke crank, 6.125˝ rods with a 4.070˝ bore. We ran AFR 260 Mongoose heads and a custom ground Brian Tooley Racing camshaft. We ran Johnson roller lifters, a Callies DragonSlayer crank with Callies billet I-beam rods and Wiseco pistons. We used ARP hardware throughout and we had a Magnuson Heartbeat supercharger with Injector Dynamics 1,600cc injectors. Laslty, we used Clevite H-series bearings and GFX HellFire rings.”

The customer is using his Camaro as a daily driver with the capability to do some racing when he wants. The 376 cid LSR set up Mullenix Racing Engines delivered makes upwards of 1,000 wheel horsepower!

“It’s a pretty good little combo,” he says. And we’d have to agree! However, the customer’s ultimate goal is to make 1,600 wheel horsepower using a twin-turbo set up in the near future!

The Engine of the Week eNewsletter is sponsored by PennGrade Motor Oil and Elring – Das Original.

If you have an engine you would like to highlight in this series, please email Engine Builder magazine’s managing editor, Greg Jones at [email protected]

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