Inside Stainless Diesel’s New Pro Mod Corvette

When you’re a three-time Pro Street champion with multiple record-setting passes under your belt, the next step in your racing career is pretty logical—you go even faster. For Stainless Diesel’s Johnny Gilbert, that meant bumping up to the Pro Mod category and building the quickest door-slammer he and his team possibly could. After scoring a proven 3-second performer—a ’63 split-window Corvette—as a roller in 2020, Johnny and his team mulled things over for several months before finalizing a game plan. The final decision? The second-generation ‘Vette would receive diesel propulsion by way of a Cummins and eventually run 3’s. The engine would be built by Wagler Competition Products, S&S would supply the fuel, MoTeC would control everything, the chassis would receive updates at Hammertech Racecars, and Rossler would get a call for one of its legendary Turbo 400s.of smiles.

With the valve cover, intake, fuel, and water lines protruding through the hood, it’s not very hard for Johnny Gilbert’s Pro Mod Corvette to pull bystanders in for a closer look. The CX400 series Cummins is the brainchild of Wagler Competition Products and boasts a dry billet-aluminum block and cylinder head. A factory 6.7L crank—micro-polished, gas nitrided, and lightened by Shaftech—moves half a dozen billet Wagler rods and de-lipped, marine pistons with Total Seal rings up and down in the 4.250-inch cylinder bores. A Wagler high-flow, billet-aluminum head anchors to the block via top fuel head studs, while the valvetrain highlights include a billet roller cam and Manton roller rockers..
Keeping an engine alive at the power levels Johnny plans to see calls for a dry sump oil system. At the heart of his engine’s dry sump setup is a pump from Peterson Fluid Systems, and it’s driven off the back of a Wagler-designed billet gear case. For the final piece in the dry-sump system, Johnny turned to Tony Derhammer of HammerTech Racecars, who fabricated the low-profile aluminum oil pan.
You won’t find zoomies on very many diesels, but they’re one of the stand-out features on Johnny’s Pro Mod. “I hate that big ass, 5-inch pipe sticking out of the side of a car, so I thought our Pro Mod needed zoomies,” he told us. “So I showed Cody Fisher at Firepunk Diesel where I wanted the gates and he took it from there.” As you can see, the 5-inch outlet on the turbo masterfully transitions into four 2.5-inch diameter pipes, while the dual 45mm external Turbosmart wastegates feed into their own 2.5-inch section.
Just like on the Pro Street truck, Johnny enlisted S&S Diesel Motorsport to handle the fuel side of the horsepower equation. Two reverse rotation, 12mm high-speed CP3s are tasked with pressurizing fuel while six top-feed style, extensively-modified Iveco-based injectors with 8-hole 6.7L Cummins nozzles head up in-cylinder delivery. The Iveco-derived injectors were chosen for their size and ultra-high pressure capabilities. As it stands currently, Johnny tells us he’s used less than 50 percent of the fuel volume available to him.

So far, things are looking pretty good. At the car’s debut race, Outlaw Diesel Revenge in Indianapolis, Johnny, and the team walked away winners. Crazy enough, the goal that weekend only entailed making a few test hits to see how the chassis reacted. When the car responded with 1.15, 1.14, and then 1.07-second 60-foots, one thing led to another and the test session turned into a full-blown race. By Saturday night, Johnny found himself in the final round, and then the winner’s circle. Not a bad start for a car using roughly half of its 3,500hp potential.

All-Aluminum Cummins

Massaged in-house at Stainless Diesel, the Garrett GT55 was treated to a billet, 5-blade compressor wheel with a 98mm inducer, a 1.37 A/R divided inlet exhaust housing, and a dual ball bearing center section. Following our photo shoot, Johnny shaved 10 pounds off of the big single by adding a billet center cartridge. While peak boost has yet to be achieved with the GT55, we’re told it’s currently seeing shaft speeds in the 98,000 to 105,000 rpm range—and that the line in the sand will be 125,000 rpm in the future. The exhaust manifold is a one-off, polished T6 piece Johnny fabricated himself.

After careful consideration, Wagler Competition Products’ CX400 Cummins got the nod for powering the car. The billet-aluminum block and head combination are completely void of coolant flow and, as expected, dissipates heat extremely well. In fact, it’s a challenge to keep heat in the engine at times. “The aluminum engine doesn’t get up to temperature as the cast-iron engine did, so it’s a learning curve,” Johnny explains. “We like to be at 800 degrees (EGT) minimum before I bring nitrous in, so we’re working with a 3-second spool-up time right now.” Thanks to locating the engine deep within the chassis, a 51-percent weight bias was achieved.

Cutting-Edge Common-Rail System

A top-feed style injector arrangement on the CX400 means there are no side feed tubes to worry about, and the injectors themselves are interesting pieces. They began life as Iveco-based units, chosen for their size (i.e. high-volume) and pressure capability (more than 36,000 psi), and through extensive modification at S&S Diesel Motorsport can easily support more than 3,000 hp. At optimum duration, they can flow 865 mm3 worth of fuel through their 6.7L-based 8-hole nozzles—but at the present time (and at roughly 1,800 hp) only 400 mm3 has been called upon. The wild common-rail injectors are supported by dual gear-driven S&S CP3s, both of which are high-speed 12mm stroker pumps. The driver-side CP3 accommodates an SP3000 mechanical lift pump, S&S’s bolt-on supply pump that’s capable of moving 3,000 LPH.

An N2O/H2O rail from HammerTech Racecars mounts to the Wagler individual runner intake, with PVC-covered braided stainless steel hoses routing to each runner. The system works with a nitrous tank getting filled with pressurized water (950-1,000 psi) thanks to a priming solenoid with a .123-inch orifice. The pressurized water enters the rail through a -8 AN line, followed by a 375 solenoid from Nitrous Express, and infiltrates the intake runners via water injection nozzles sourced from Scheid Diesel. The water injection system is easily tunable.
A CP3-married supply pump, coined S&S Diesel Motorsport’s SP3000, is coupled to the driver-side CP3 (and both CP3s are gear-driven thanks to the previously-mentioned Wagler billet gear case). Capable of flowing 3,000 LPH, the mechanical supply pump provides the CX400 Cummins with 150-psi at idle and 250-psi down the track. It’s used in conjunction with S&S’s regulated filter head. As for lifeblood, Johnny runs Scheid Diesel’s Lightning fuel, along with a dose of lubricity additive from Hot Shot’s Secret.

Big Single, Zoomies, Nitrous, And Water With Johnny’s company, Stainless Diesel, a major player in the turbo game, it only made sense that a charger of his own design made the cut. The in-house-modified GT55 sports a 98mm, 5-blade billet compressor wheel, a dual ball bearing center section, and hangs from a one-off, T6 polished Stainless Diesel exhaust manifold Johnny fabricated himself. The manifold also integrates the piping required to feed a pair of 45mm Turbosmart wastegates. The rest of the exhaust is perhaps the most captivating feature of the car: five 2.5-inch diameter zoomies. Void of an intercooler, intake temps and EGT are kept in check with a combination of nitrous and water, with the nitrous stages’ primary purposes being to shorten spool up while staging and adding horsepower down the track.

Applying Power With Proven Drivetrain Parts

Though he admits the big tires will take some getting used to, Johnny’s love of Hoosier slicks has carried over from his Pro Street program. The 17.0/36.0-16 Hoosiers are mounted to 16-inch Spin Werkes Racing wheels, while the skinnies up front measure 27.0 x 4.5-15. Though Johnny is glad his days of worrying about torque steer are over, he and the Stainless crew have already had to tune around a few tire chatter issues on the Corvette—something that we’re sure will get ironed out with more seat time.
As is the case in Johnny’s 2,800hp Pro Street Dodge, a Turbo 400 got the call for the Pro Mod—and the biggest name in TH400s put this one together: Rossler Transmissions. The lockup unit has yet to really be leaned on, and in fact, has only seen lockup on one occasion so far, but rest assured with a bit more seat time Johnny will put the Sun Coast bolt-together converter to good use. Interestingly, unlike other Pro Mods, Johnny and the team made sure the transmission could be pulled from beneath the car, rather than out one of the doors.
Full control over the Wagler CX400 comes courtesy of a stand-alone MoTeC ECM, and its accompanying 12-inch wide C1212 display is pictured here. Similar to Stainless Diesel’s Pro Street program, Johnny has his son, John Gilbert III (J3), in charge of navigating the MoTeC software and writing the race-winning calibrations. According to Johnny (and on behalf of J3), so far they’ve found the MoTeC system more user-friendly than the Bosch system employed on the Pro Street truck, which means figuring out the perfect tune-up could come sooner rather than later.
It goes without saying that safety is a priority in a Pro Mod, and driver comfort is a big part of the safety equation. For perfect fitment in the cockpit, HammerTech Racecars set Johnny up with a foam-poured race seat, custom-molded to his exact body structure. These are the behind-the-scenes touches that often go unmentioned and unnoticed in a high-caliber build like this, but that in no way minimizes their importance. It’s a fact that, while real estate inside the cockpit is exceptionally tight, Johnny is very comfortable.

Campaigning a TH400 (and a four-wheel drive version, no less) in Pro Street convinced Johnny and his team long ago that the proven three-speed transmission was the best path to going fast while also enjoying relative longevity. For Pro Mod, a Rossler-built TH400 sits behind the Cummins, and a Sun Coast 5-disc, bolt-together lockup converter handles power transfer. Once through the TH400, a carbon fiber driveshaft routes power to a Pro Mod 9-inch rear end and ultimately a pair of 36-inch Hoosiers. A fine-tunable four-link from Tim McAmis Performance Parts aids the power-planting effort, while Strange Engineering carbon brakes all the way around help bring the car to halt after the parachutes have been deployed.

The Road To The 3’s (Has Begun)

Double-adjustable struts with Hyperco springs from Strange Engineering exist up front, along with the company’s carbon brake kit. Not only do the carbon rotors and pads save weight, but they resist brake fade, provide significantly improved stopping power, and resist deflection much better than stamped stainless steel. Little things like this demonstrate the fact that the car’s safety provisions are just as cutting-edge as its power plant, electronics, or transmission.
It’s no surprise which rear axle is under the Pro Mod, but it’s the ring and pinion that revealed some of Johnny’s eighth-mile plans. The 9.5-inch Richmond 3.25 gear ratio will allow the ‘Vette to tap 208 mph through the eighth mile if his calculations are correct, and all 3,400 to 3,500 ponies can be applied to the track. Strange Engineering’s Pro Race Hy-Tuf, gun-drilled, 40-spline axles are also along for the ride, and the rear suspension can be fine-tuned thanks to a four-link kit from Tim McAmis Performance Parts.
There’s a lot of serious hardware in this photo: 12-pound composite NX nitrous bottles (which are roughly half the weight of conventional nitrous bottles), the Reid case of the Rossler TH400, the Browell blow-proof bell housing, and the Precision Performance shifter to name a few. As for nitrous, three NX Lightning 375 solenoids are in play, along with a .122-inch solenoid for spooling up. On each pass down the track, roughly 8 pounds of N2O is consumed—along with 32 ounces of water.

In a previous life, the split-window Corvette went 3’s as a big-block nitrous car—so it’s no wonder Johnny is convinced it can do it again, only this time under diesel propulsion. With a past that saw him campaign a 4,400-pound 4×4 truck in a reliable, 4.8-second fashion, there is no reason to doubt his current, 3-second, 200-plus mph ambitions. How long it will take to get there remains to be seen, but don’t be surprised if—just as he did with his Pro Street program—Johnny begins to gradually chip away at his goal and eventually ends up going rounds in the 3’s. Like other diesel racers that put the Pro Mod world on notice, Johnny plans to further help put oil-burners on the map among the fastest door slammers in existence. In his own words: “We’re ready to give them a run for their money in a diesel.”

Although Johnny and his team planned to ease the car into the Pro Mod world, you never would’ve guessed that was their goal at Outlaw Diesel Revenge in Indianapolis. There, an initial 1.15-second 60-foot gave way to a 1.14 the next time out, which morphed into 4.70s right off the bat. As eliminations approached, 4.50s and a 1.07-second 60-foot fell into place and Johnny ended up in the finals, eventually even taking the win. Rest assured, Johnny and the folks that strung together three Pro Street championships will soon be in hot pursuit of a Pro Mod title. Of course, turning up the wick and running 3.70s or 3.80s would be welcomed as well…

 

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