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Diesel of the Week

Single-Turbo 6.7L Cummins Pro Mod Engine

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To people outside of the competition drag racing world, it may look like racers just build a fast car and then race it down the track for a few seconds. I’ll be the first one to admit that before I dove headfirst into the industry, I wasn’t aware of the intricacies of the sport and the insane amount of science, engineering, planning and prep that goes into a proper drag race build – all for a few seconds of barreling down the track.

Johnny Gilbert’s Pro Mod Corvette features an all-billet 6.7L Cummins engine.

A proper chassis, tires and transmission are all pieces of the pie, but the blueprint for a competitive race car (or truck) ultimately starts with the engine – and the goals you want it to achieve. While there are a few viable choices as a base, the 6.7L Cummins is certainly a standout in terms of raw horsepower capability and reliability in the diesel landscape. Diesel motorsports have progressed far enough over the past 20 years that some builders out there have all but perfected the art of building a good Cummins engine. Johnny Gilbert of Stainless Diesel recently worked with Jeremy Wagler and Wagler Competition to do just that.

Stainless Diesel is a family-owned business specializing in single and twin-turbo piping kits, billet 5-blade turbo upgrade compressor wheels, and personalized complete turbochargers. Outside of supplying shops with cutting-edge products and manufacturers their own Stainless exhaust manifold, owner Johnny Gilbert and his team of racers, pullers and chassis builders have made a name for themselves in the motorsports community.

Most notably, Gilbert holds the record for the fastest diesel pro-street truck with his common-rail Cummins. In 2020, he set the eighth-mile record with a time of 4.92-seconds at 155.7 mph. Thanks to a single-turbo 2,300 hp engine and tons of time in the garage spent tweaking and tuning their setup, the team still holds the record today.

We caught up with Gilbert at the Ultimate Callout Challenge this year, but he wasn’t campaigning his usual Dodge. Instead, he brought a more recent project that the team has been working on over the course of the last year or so: a diesel-powered Pro Mod Corvette.

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As you could have guessed, Gilbert opted to drop in an all-billet 6.7L Cummins under the hood of the ‘vette. A fairly new setup on the engine carried the team to a new personal best time at UCC in the 4.50-range.

The beast of an engine is designed for around 3,000 horsepower, and Gilbert says that with the fuel quantity and capability of the engine, it may be able to reach the 3,200-3,500 horsepower range at some point in the near future. For now, in the early stages of getting used to the new setup, it sits right around the 2,000-horsepower mark.

“Jeremy Wagler from Wagler Competition products engineered the whole thing top to bottom for us,” Gilbert says. “It’s a 6.7L Cummins crankshaft with 4.250″ bore pistons, a roller camshaft, Manton rockers, two S&S CP3 12mm fuel pumps and 600% injectors.”

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The crank was balanced and nitrided by Shaftech, improving its bending strength during cycling and allowing for less fatigue over time. Likewise, the piston tops and skirts were both coated to reduce friction. Rounding out the rotating assembly are Wagler’s heavy-duty connecting rods.

To save some extra weight, Gilbert decided to completely bypass running an intercooler.

“We’re running what we call a nitrous cannon,” he says. “It injects a tremendous amount of nitrous to bring the fuel curve on the leaner side. We were 30:1 on our last pass and our gas brothers, they’re like 12:1 on a pass like that.

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“We have full nitrous pressure, so 900 lbs. or so. We like to start around 950 in the burnout box and that’ll peel off 20 or 30 lbs., then we’re on the line and its around that 900 mark.”

For the air setup, Gilbert runs a single 98mm GTX based unit that the team builds at the Stainless shop. It has a fairly unique exhaust housing that’s divided to help it spool quicker, unlike gas cars which typically have open or non-divided exhaust.

When Gilbert’s out making a pass, quite a bit of boost is being produced. The engine has two Turbosmart wastegates, which typically get opened at around 90 lbs. of boost.

“It continues to make boost, but we control the turbo shaft speed a little bit by doing that,” Gilbert notes. “Right now, it’s in the 150 lb. boost range and the turbo shaft speed is still in the safe zone for us right at around 100,000. We try to stay away from that 120,000 rpm range because that’s the danger zone.”

Gilbert’s diesel ‘vette is already shaping up to be a powerhouse build, but he still has lofty goals on the horizon. One of them is getting closer to that 3,000-horsepower mark. The other, to eventually be able to compete with the gas-powered Pro Mod guys.

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“I think we need to really get down in that 3.80-second at 200+ mph range to be in the pack with those guys, but we can do it.”

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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