Diesel of the Week is presented by
At the 2025 PRI Show, the Fleece Performance booth served as the backdrop for one of the most purpose-built diesel combinations currently taking shape in the sport. Standing alongside it is owner Chris Buhidar of Truck Source Diesel – a name well-known to anyone paying attention to modern diesel drag racing.
This engine combination isn’t just another iteration of a proven Cummins platform. It is the culmination of years of hard lessons, broken parts and a deliberate reset.
“We’ve been talking about building a new truck from the ground up with all the things that we’ve learned over the past few years, and we finally got around to it,” Buhidar told us.
That reset is anchored by a billet 6.7L Cummins platform built by Fleece Performance – an engine that blends proven architecture with carefully selected upgrades aimed at surviving, and winning, at the 3,000-plus horsepower level.
Starting Over with Purpose
Chris’ previous Truck Source Diesel platform had reached a point many racers know all too well – fast enough to be competitive, but stuck between classes and constantly pushing beyond its intended limits.
“The old truck… ended up in a no man’s land,” Buhidar explains. “It was still a little too heavy and big to compete in Pro Street, but it was too fast to slow it down… and we broke more stuff than we should have broke trying to go faster than we should have been.”
That experience dictated the philosophy behind the new build. Rather than chasing incremental gains, the team opted for a clean-sheet approach – building a chassis and powerplant combination designed specifically for where they wanted to compete, not where they had been.
The Billet Foundation
At the core of the package is one of Fleece Performance’s billet Cummins blocks. For engine builders, the advantages are obvious – rigidity, strength and the ability to control critical dimensions under extreme cylinder pressure. Plus, billet blocks make potential fixes a little easier too.
This particular engine maintains a familiar displacement strategy, sticking with what Buhidar describes as a “proven combo.”
“It’s still a 6.8L like we ran in the UCC truck for a long time,” he notes. “We’re familiar with the power band.”
That slight increase over a traditional 6.7L comes from a modest overbore – approximately .040” over – paired with a non-standard deck height configuration. The altered deck height allows for improved rod ratio and piston geometry under high boost conditions, while also accommodating the ring package and combustion strategy the team has refined over time.
From a machining standpoint, billet blocks open the door to tighter control over bore geometry and cylinder stability, especially important when operating in the 90-100 psi boost range this engine is expected to see.
Cylinder Head and Valvetrain Strategy
Sitting atop the billet block is a Wagler cylinder head, but like much of this engine, it doesn’t remain untouched.
“It is a Wagler head, but Fleece does their own valvetrain and some of their own spin on it,” Buhidar notes.
Despite the extreme performance targets, the engine retains a factory-style rocker architecture. That decision reflects a broader trend in high-end diesel builds – maintaining proven mechanical simplicity while upgrading materials, geometry and stability.
Rather than chasing radical redesigns, the emphasis is on controlling valvetrain motion under high cylinder pressure and elevated engine speeds. Stability, not novelty, is the priority.
Rotating Assembly
One of the more interesting aspects of the build is the decision to retain a relatively conservative rotating assembly configuration.
“It’s a pretty stock crank… Diamond pistons with their ring pack, they have dialed in pretty good,” Buhidar says.
In an era where billet cranks and ultra-exotic materials are readily available, this choice highlights the importance of understanding load paths and durability thresholds. A properly prepared OEM-based crankshaft, when paired with a rigid block and optimized balance, can still deliver the reliability needed at extreme power levels.
The Diamond piston and ring package plays a critical role here. Ring seal becomes increasingly difficult as boost climbs into triple digits, and maintaining consistent cylinder pressure without excessive blow-by is essential – not just for power, but for durability.
Single Turbo, Big Air
Airflow is handled by a Garrett GT55 turbocharger with a 102mm compressor.
“It’s actually the turbo that we used to run on Wade’s Pro Mod,” Buhidar says.
That choice speaks volumes. Rather than chasing multi-turbo complexity, this combination relies on a large-frame single turbo, supported by aggressive fueling and nitrous to manage spool characteristics and overall airflow demand.
At the projected power level, boost pressure is expected to land in the 90–100 psi range. At this level, compressor efficiency, intercooling strategy – air-to-water in this case – and turbine flow become just as critical as peak pressure.
Fuel System and Engine Management
Fuel delivery is handled by S&S Diesel Motorsport components, including their 650 pumps and Ordnance injectors.
This level of fueling capacity is necessary to support both the base power level and the additional demand introduced by nitrous oxide. The system is controlled by a MoTeC ECU, providing the precision required to manage injection timing, duration and multiple stages of nitrous activation.
At 3,000 horsepower, mechanical components alone are not enough. Calibration becomes just as important as hardware, and the ability to control combustion events precisely can make the difference between a clean pass and a catastrophic failure.
Nitrous
While the base combination is formidable on its own, nitrous oxide is a central part of the strategy.
A five-kit nitrous setup from Nitrous Outlet will allow Chris and his team to manage power delivery progressively – bringing the truck into the powerband cleanly before applying full output down track. This is especially important in a four-wheel-drive chassis, where traction management becomes a limiting factor.
“With it over 3,000 hp, the trick will be getting a four-wheel-drive chassis to take that much all the way down the track,” he explains. “But it’s a similar setup to what we run on Crazy Horse.”
Drivetrain and Chassis
Behind the engine is a Rossler TH400 lockup transmission paired with a Neil Chance transfer case and driveline components the team has already proven in competition.
The more radical departure lies in the front suspension.
“We built… an IFS front end, which is a little bit different,” Buhidar says.
Independent front suspension is relatively uncommon in high-end diesel drag trucks, particularly in four-wheel-drive applications. However, the potential advantages – reduced weight and improved traction characteristics – made it worth exploring.
“We feel like there might be an advantage, not just weight, but traction,” he adds.
This is a notable trend to watch. As power levels continue to climb, traditional solid axle setups may begin to give way to more refined suspension solutions aimed at maximizing tire contact and consistency.
A Different Kind of Build Philosophy
Visually, the truck also breaks from convention. Rather than a full Pro Mod-style fiberglass body, the team retained factory aluminum panels.
“The body, it’s all aluminum, it’s all OE panels. There’s no fiberglass on it. We kind of wanted to do something that didn’t look like a Pro Mod,” Buhidar says.
That decision reflects the overall theme of the build – purpose-driven, but grounded in realism and identity.
Despite the capability of the combination, Buhidar is clear about the objective.
“We’ve never chased records… we like winning points championships, so as long as it’s faster than the guy in the next lane, that’s good for us,” he admits.
Still, the performance targets are ambitious.
“Hopefully we can get it into the bottom 4s… we intend to race NHRDA, ODSS and we’d like to do some small tire racing with it,” he adds.
This billet Cummins program highlights several key trends shaping the future of diesel performance. Most importantly, it reinforces a principle that applies at every level of racing – progress comes from experience. And in Chris Buhidar’s case, that experience has been hard-earned.