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A 1,000hp, 2.6 Smooth Bore Duramax

When Lee Stiltz replaced his V-10 Dodge with this ’05 Silverado 2500 HD his senior year of High School it was a definite upgrade. But just two years later, the ¾-ton Chevy was already being retired from daily driving duties. Since the truck pulling addiction took hold, Lee has embarked on an intense, six-year ride that’s brought him to the top of every pulling class he’s tried his hand in: Work Stock, 2.5, and now the 2.6 smooth bore category. In the truck’s current state, the LBZ Duramax under the hood belts out more than 1,000 hp and it rarely finishes outside of third place..

1,000+ HP At the Crank

When the 8,000-pound Pro Street (2.6 Smooth Bore) class was in its infancy, Lee was able to earn a points championship with an engine that dyno’d 880 hp. The year after that, he turned in a repeat performance with an 895hp combination. But not unlike other air-limited pulling classes, turbo technology took off in a big way last year—with Lee being the beneficiary of 120 more horsepower. His current parts recipe turned out 1,013 hp on the engine dyno…not bad for a 66mm smooth bore charger and cylinder heads that’ve hardly been modified.

Bottom-Up Build

Starting with an LBZ-based block at Diesel Technology Source, the water jackets were 75-percent filled with concrete and an internally balanced Ultra Billet crankshaft from Callies was fastened in place via ARP main studs. Forged Carrillo rods attach to fly-cut and thermal coated billet Diamond Racing pistons by way of Trend Performance H11 wrist pins, a custom grind alternate fire cam from DTS sits in place of the factory unit, and a Wagler pinned oil pump keeps ample Cen-Pe-Co oil circulating at full tilt. Slight massaging of the exhaust ports, SoCal Diesel beehive valve springs and billet rocker bridges were the extent of the mods performed on the heads, which are secured to the block by ARP Custom Age 625+ studs.

Custom-Tailored Fuel System

Working closely with the common-rail experts at S&S Diesel Motorsport, Lee was able to piece together an injection system that performs just as well on the track as it did on the dyno. Called its Ordnance LBZ Air Limited Spec injectors, the S&S units move torrents of fuel in a very quick manner, hence why only 1,200 to 1,300 microseconds of duration (commanded via tuning) is all that’s needed to make four-digit power. LLY rails, selected for their superior flow capabilities, store the pressurized fuel supplied by a dual CP3 arrangement that’s anything but ordinary. A 12mm stroker pump, dwelling in the factory location, combines forces with a reverse-rotation, belt-driven SuperSport pump that makes use of S&S’s new, gear-driven CP3-coupled fuel supply pump. Proper fuel filtration and supply pressure is achieved with the company’s brand-new regulated filter head assembly.

Hart’s Turbo

Stepping up to a T6 turbocharger from Hart’s Diesel has paid big dividends so far. As Hart’s always seems to do, this unit has outperformed all other 2.6-inch smooth bore chargers to date and Lee says he’ll be holding onto it for a while. The non-map groove, Garrett-based turbo makes use of a billet 66mm inducer compressor wheel, a dual ball bearing center section, and a sizeable turbine wheel inside a relatively tight, 1.00 A/R exhaust housing. The T6 flange charger mounts to a Wehrli Custom Fabrication T4 pedestal and exhaust collector through the use of a T6 to T4 adapter and sends boost through a Bell air-to-air intercooler via Wehrli piping. The velocity stack and air guillotine came from Show-Me Performance.

Sled-Ready Allison

No amount of horsepower is worth making if you don’t have a transmission that can hold it, so Lee turned to the Allison gurus at Illini Outlaw Diesel to prep his transmission for battle. All billet shafts, a billet C2 clutch hub, Raybestos clutches, and a 3,200-rpm stall Sun Coast converter all got the call, along with a Fleece Alli-Locker for precise control over lockup and a Merchant Automotive rear housing support for exterior reinforcement. With the truck’s 4.56 ring and pinion, Lo side selected in the transfer case, and 900-ish horsepower making it to the ground, Lee has no problem carrying fourth gear all the way down the track.

A Constant Contender

The Pro Street class is one of few remaining precincts in truck pulling where the competition isn’t largely dominated by Cummins. And in working with some of the biggest names in the Duramax world, Lee aims to keep it that way. One of the busiest pullers we’ve met, Lee has already accumulated more than 300 hooks in the truck’s first six years of action. And with that experience has come many wins, including two Pro Street points championships in the Illinois Tractor Pulling Association, as well as two Work Stock titles and one 2.5 class championship in the United Pullers of America organization. Throw in a Third Place finish at the 2019 Scheid Diesel Extravaganza and a Second at Diesels in Dark Corners and you’ve got a Duramax that’s highly competitive on the national level. With both of those aforementioned events still on the books for 2020, be on the lookout for this hard-charging Bow Tie in Pro Street. Chances are good you’ll find it somewhere beyond the 300-foot mark.

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At first glance, and thanks in large part to the massive turbo near the cowl, it’s hard to believe this is a truck you’d find in the 2.6 smooth bore class, but it just goes to show how serious this field has become over the last few years. And the LBZ Duramax sitting in Lee Stiltz’ ’05 Silverado is as serious as the charger that feeds it. The short-block was pieced together by Diesel Technology Source and sports a Callies Ultra Billet crankshaft, ARP main studs, Carrillo rods, fly-cut and coated Diamond Racing pistons, and a custom grind alternate fire camshaft.

 

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Driving the Hart’s charger is made easier through the use of PPE High-Flow high-sil moly exhaust manifolds coupled to 2-inch stainless steel up-pipes from Wehrli Custom Fabrication. For an additional increase in flow, the heads were port-matched to the exhaust manifolds. As for the LBZ heads themselves, they benefit from SoCal Diesel beehive valvesprings and billet rocker bridges, and anchor to the block by way of ARP Custom Age 625+ head studs. Also notice the glow plug delete bolts from Merchant Automotive.

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Dual CP3’s from S&S Diesel Motorsport are used to effectively support the high-flow injectors in the engine. One of S&S’s 12mm stroker pumps resides in the factory location, while the second SuperSport CP3 (shown here) is a belt-driven, reverse-rotation unit fitted with the company’s new gear-driven lift pump. The CP3-married fuel supply pump provides 152-psi at idle, 350 psi at wide-open throttle, and has the capability to flow as much as 3,000 l/hr.

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This 2.6-inch smooth bore turbo from Hart’s Diesel is the primary reason Lee’s engine turns out 120hp more than it used to. The Garrett-based charger features Hart’s hubless, 66mm billet compressor wheel and a dual ball bearing center section. On the exhaust side, a turbine wheel larger than 100mm in diameter lives inside a 1.00 A/R housing. The hefty T6 charger mounts to a Wehrli Custom Fabrication T4 pedestal with the appropriate adapter. On looser tracks, Lee gets 40 to 42 psi of boost out of it, but on hard-packed biting surfaces that number can jump to 60 psi. We’re told drive to boost pressure is 1:1 in either case.

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S&S Diesel Motorsport’s regulated filter head was designed to be paired with its gear-driven fuel supply pump. It features a built-in fuel pressure regulator, a factory Cummins mounting flange, a fuel distribution block, and inlet and outlet ports. The regulated filter head also has provisions to support as many as four CP3’s—perfect for the company’s Super Stock clientele.

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In the ultra-competitive world of truck pulling, where the Cummins is usually king, Lee’s hard-running Duramax is known to shake things up—especially when you take into account that he rarely finishes outside of the top three. As a play on a running joke among the competition that a Duramax can’t run good unless it’s ingesting nitrous, Lee found it all too fitting to repurpose this 24-ounce can of NOS as his coolant overflow.

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A set of high volume, quick-firing “Ordnance” injectors are tasked with getting fuel in-cylinder. Built by S&S Diesel Motorsport specifically for Lee’s engine, the LBZ-based units have received body modifications and been fitted with nozzles that measure more than 300-percent over. Linking the injectors to the CP3’s are rails sourced from an LLY application, which are said to be the highest flowing rails to grace the Duramax lineage.

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The truck’s interior is stripped down, but it isn’t gutted completely. Per the Pro Street (2.6) class rules mandated by the Illinois Tractor Pulling Association and the Pro Pulling League organizations he hooks with, the truck’s factory dash, steel firewall, and electric glass windows haven’t been touched. Also notice the Wagler billet hand throttle, the race seat he obtained from Orr’s Diesel, and the manual fuel dump (the air knife cable is located under the hood latch release).

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Tied in with the toggle switches that control the electric water pump, power steering pump, and intercooler and radiator fans, Lee mounted an Alli-Locker from Fleece Performance Engineering, which allows for full control over converter lockup. On loose tracks, Lee tells us he couples the converter 50 to 60-feet out so as to avoid blowing the tires off. On a tighter track where traction is virtually guaranteed, he hits it as soon as rpm comes up.

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Concealed under a mandatory transmission blanket (this one from DJ Safety) sits an Allison 1000 that was pieced together by Illini Outlaw Diesel. Billet input, intermediate, and output shafts, a billet C2 clutch hub, Raybestos clutches, and a 3,200-rpm stall speed, billet stator triple-disc Sun Coast converter highlight its upgrades. For additional reinforcement, Merchant Automotive’s rear housing support links the Allison’s tail housing to the factory transfer case.

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With a factory-based rear axle being mandated in Pro Street, what’s better than a done-up 1150 AAM? This hybrid version from Performance Pros has proven indestructible over the past three years of abuse. It houses 38-spline, 300M, gun-drilled axleshafts, a spool, and 4.56 gears.

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The factory torsion bars may be long gone, but the OEM-based 9.25 AAM IFS survives under the front of the truck. Double adjustable, dual coil over AFCO pulling shocks from Performance Pros allow compression and rebound dampening changes to be made completely independent of each other. Making them fit called for the use of beefy, U-shaped upper control arms. The way Lee has things configured, this suspension arrangement essentially provides zero downward travel and very limited upward movement.

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A single rear wheel stipulation keeps the Pro Street class interesting, as well as its DOT tire rule. To dig him through the dirt, Lee relies on the trusty Trxus STS from Interco—a tire that’s been a huge hit in truck pulling without ever really penetrating any other form of off-road motorsport. They measure 35×12.50R16 and sit on 16×10-inch aluminum Real Racing Wheels.

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Eliminating all weak links in the factory IFS steering system, PPE’s Stage 3 tie-rods sit in place of the flimsy stockers, and the company’s idler and pitman arm braces were also bolted in place. And because Lee’s dedicated puller really only needs to drive in a straight line, a 304 stainless-steel straight center link (also from PPE) replaced the OEM unit. As for power steering, nearby Dermody Diesel Performance built the truck’s electric-over-hydraulic system. Also notice the RCV Performance Ultimate IFS CV axles.