In the world of competitive diesel truck pulling, Cummins is king. But in the sport’s DOT tire classes, Duramax die-hards would vehemently disagree with that sentiment. After all, GM owners have long been going head-to-head with the I-6 competition for years and seen solid success while doing it—especially in the 8,000-pound Pro Street category. This is where you’ll find Lee Stiltz and the ¾-ton ’05 Chevrolet Silverado he calls “Privileged.” Lee’s dug his way to countless victories over the years behind the wheel of this truck, as well as earned a handful of championships. So he must be doing something right.
Despite packing a single, 66mm turbo, the 6.6L LBZ produces more than 1,000 hp on fuel alone. It’s all made possible thanks to having cutting-edge common-rail fuel system technology onboard, as well as a reputably-built short-block and the aforementioned turbocharger, which is anything but an off-the-shelf unit. A heavily-reinforced IFS front-end, a bombproof AAM 1150 and a battle-prepped Allison transmission help the truck get as much of that four-digit horsepower to the ground as possible. Fresh off a clean-sweep of the Missouri State Fair and a number 1 qualifying hook at the Scheid Diesel Extravaganza, we caught up with Lee—and you can find all the gory details on his hard-charging Duramax below.
Dyno-Proven Duramax
At the heart of Lee’s dirt-slinging Silverado you’ll find an LBZ Duramax that made a dyno-proven 1,013 hp in 2020. The short-block, assembled by Diesel Technology Source, boasts an Ultra Billet crankshaft from Callies (along with ARP main studs), Carrillo rods, valve-relieved and coated Diamond Racing pistons and a custom grind, alternate firing order camshaft. Factory-based, CNC-ported cylinder heads allow the 6.6L V-8 to breathe freely and are anchored to the block via ARP Custom Age 625+ head studs. Of course, none of that is visible in the image above, thanks to the engine’s massive, class-specific turbocharger and corresponding piping consuming most of the view.
66mm Turbo
In a class where you’re air limited thanks to turbo restrictions, the best turbocharger builders in the business always seem to come up with a way to make the most of the situation. For Lee’s needs, he turned to Hart’s Diesel, a big name in custom turbo and fuel system components, especially in the tractor pulling arena. In this application, Hart’s built a Garrett-based, smooth bore (i.e. no map groove) charger with a 66mm (2.6-inches) compressor wheel inducer. The giant, T6 flange exhaust housing conceals a turbine wheel that exceeds 100mm and the turbo also features a custom, dual ball bearing center section. Hart’s “little” 2.6 turbo creation builds as much as 60-psi of boost when Lee storms down the track.
Electronically Controlled, Mechanically Supplied
Aside from the leading-edge turbo, a next-level fuel system from S&S Diesel Motorsport represents much of the magic behind the LBZ’s four-digit horsepower number. The engine still makes use of common-rail injection, but two CP3 high-pressure pumps are employed—both of which are 12mm stroker pumps. One CP3 lives in the factory Duramax location, while the second is a belt-driven, reverse rotation unit with S&S’s SP3000 supply pump coupled to it. The gear-driven lift pump provides more than 150-psi at idle, 350 psi at wide-open throttle and is capable of flowing as much as 3,000 liters per hour. LLY fuel rails store the highly-pressurized diesel and 300-percent over injectors distribute fuel in-cylinder.
Control Center & Hand-Throttle
Although Pro Street class rules dictate that a truck’s factory dash, steel firewall and glass windows have to remain, competitors can scrap pretty much everything else. Despite the name of the class, however, much of the streetability is gone, as is evident in the Wagler billet hand throttle shown here. Down at the toggle switches, Lee has the power to manually control the engine’s water pump, power steering pump, intercooler fan and radiator fan. The white knob to the right of the toggles is the DSP5 switch that allows Lee to change between custom ECM tuning files.
An Allison Prepped For Pulling
Underneath the transmission blanket, you’ll find a six-speed Allison 1000 that was pieced together by Illini Outlaw Diesel. Billet input, intermediate and output shafts, a billet C2 clutch hub and Raybestos clutches highlight the internal upgrades. A loose, 3,200-rpm stall speed, triple-disc torque converter from Sun Coast helps bring the turbo to life on the starting line and an AlliLocker from Fleece Performance Engineering offers Lee full control over converter lockup.
Heavily Reinforced, GM IFS
In order to tolerate the stress that comes with 1,000 hp and 35-inch Mud Grapplers clawing their way to the 300-foot mark, the truck’s factory 9.25 AAM IFS system was treated to major reinforcements. First and foremost, RCV Performance Ultimate IFS CV axles were added, followed by beefy Stage 3 tie rods, idler and pitman arm braces and a 304 stainless steel straight centerlink from PPE. AFCO double-adjustable dual coil over pulling shocks from Performance Pros help dial-in suspension travel (or lack thereof) and an electric-over-hydraulic power steering system was built by Dermody Diesel Performance.
An AAM 1150 On Steroids
A fortified AAM 1150 from Performance Pros resides in the rear of Lee’s Silverado, and it’s about as bulletproof as it gets for a factory-based axle. Treated to 38-spline, 300M axle shafts that’ve been gun-drilled to save weight, 4.56 gears and a spool, it’s yet to skip a beat or fail to keep the rear tires digging considering all the abuse it sees.
A Cut Above The Rest
When everyone is on what is apparently a level playing field given the strict rulebook competitors have to abide by, even the slightest edge in horsepower can make a major difference out on the track. In addition to making what is probably close to the most horsepower in the Pro Street class, a proven chassis and plenty of driving experience also play into Lee’s favor when he hooks to the sled. With some pretty big wins in 2021, look for his front-running Bow Tie to do more of the same next season.
Keyword: Dominating The Dirt: An Inside Look At A Duramax-Powered, Pro Street Diesel Sled Puller