A 1,150-HP Triple-Turbo LB7 Duramax

There’s something about your first truck that makes it special. Whether it’s a clapped-out beater, a show truck or something in between, the first one is always special. While many of us have moved on from our first trucks—willingly or unwilling—most of us wish we still had them. Jason Wehrli now owns Wehrli Custom Fabrication in Sugar Grove, Illinois, where he builds high-performance diesel parts and trucks, but he got his start with Duramax diesel engines years ago when he was only 18 and still in high school.

The 2002 Chevy 2500 HD Crew Cab seen here was purchased in 2007 with 80,000 miles on the odometer. While the truck was in good condition, any gearhead worth his wrenches doesn’t leave his truck stock for long. Over the past few years, Wehrli has transformed the truck from stock to wild by completely rebuilding, upgrading and beefing up the complete drivetrain from front to rear to make the truck stronger and more capable than ever.

Wehrli chose to keep the exterior modifications to the truck on the subtle side with a mild lift, aftermarket wheels and tires, and a custom cowl induction hood. Sharp-eyed onlookers will also spot the solid front axle that replaces the factory IFS. The real beauty of his truck lies beneath the skin and makes the truck one heck of a beast, thanks in part to the triple-turbo Duramax under the bulged hood.

Wehrli started customizing his truck right off the bat and tells us that it has had wild compound turbo systems on it almost since day one. Before the first turbo upgrade went on the truck, he wisely upgraded the Allison transmission. He rebuilt the transmission with Sun Coast parts, including billet input, intermediate and output shafts, as well as their clutch kit and billet torque converter. A deep Mag-Hytec pan is used to hold additional fluid and help keep the transmission cool while working with the front-mounted transmission cooler and electric cooling fan. The converter is linked to the Duramax engine with an SFI-approved billet Sun Coast flexplate. Output from the Allison transmission is handed off to an NP273 transfer case that he installed as an upgrade to the 263 that comes standard in Duramax trucks and has been known to have issues. Front and rear outputs from the transfer case both utilize custom-built steel driveshafts with 1480 U-joints to handle the power from the engine.

In continuing with the driveline strengthening, Wehrli removed one of the weakest links of the GM trucks by swapping out the IFS with a Dana 60 straight axle from an ’85 Ford. To get the power to both wheels he installed a Detroit Truetrac differential with new 4.11 gears. Most straight axle conversions we see ride on leaf springs with a huge lift, but he wanted to keep his truck much more practical and at a reasonable height so he fabricated a custom parallel four-link suspension setup with air bags and dual Bilstein shocks on each side. He also fabricated the panhard bar to keep the axle located in the chassis as well as the anti-sway bar to keep the body flat in the turns. Steering is handled by crossover steering linkage with a drop Pitman arm and a single steering stabilizer to keep the big truck pointed in the right direction.

Wehrli opted to retain the factory 11.5-inch AAM rear axle but knew better to rely on the factory differential and axles. He replaced the factory diff with a Yukon Grizzly locker built to accept larger and stronger Yukon 38-spline axles. Like the front, a new set of 4.11 gears replaced the factory gears when he was upgrading the rest of the internals. Stock springs and 3-inch blocks provide the proper stance in the rear while a pair of Bilstein shocks control the ride and keep the axle in check. The truck rides on a set of 18×9 Ultra wheels wrapped in 35×12.50R18 Nitto Trail Grappler M/T tires on all four corners.

After various turbo setups on the stock LB7 Duramax engine, Wehrli finally went all out and tore down the engine to build it up one final time as the wild triple-turbo/triple-CP3 monster that currently resides in the truck. The block was sent over to Pfeiffer’s Race Engines in Freeport, Illinois, to be bored .020-over and reassembled using a stock crank, Carrillo rods and Mahle forged pistons with a 16.5:1 ratio. The short block was capped with stock heads that were disassembled and ported by the crew at Pfeiffer’s, then reassembled with SoCal Diesel valve springs and Hamilton push rods to actuate the rocker arms. The heads are secured to the block with a set of ARP head studs to keep the cylinder pressures contained.

After Pfeiffer’s completed the engine assembly, Wehrli went to work on completing the build. He installed a set of Bosch Motorsport 150% over fuel injectors from Exergy to deliver more fuel. The high-flow injectors are fed by three factory GM CP3 high-pressure fuel pumps mounted on custom bracketry that he fabricated. A FASS 260-gph fuel filter and pump system delivers fuel from the tank to the trio of CP3s. He also built one of his aluminum intake manifolds to top the engine and deliver the compressed charge into the ported cylinder heads much better than the factory manifolds.

On the exhaust side of the heads, Wehrli fabricated a set of log-style headers along with plumbing and mounts for not one or two, but three S400-based Engineered Diesel turbochargers under the hood on the passenger side of the engine bay. The top two turbos draw in atmospheric air through a pair of large cone filters, then compress and pass it along to the lower charger before the air charge is delivered to the C,G&J high-flow charge air cooler with cast aluminum end tanks. Spent exhaust gasses are fed from the headers into the lower charger, then into the two upper chargers and out to the rest of the 5-inch diameter polished stainless steel exhaust system. To get the most out of the engine combination, Wehrli turned to the team at Duramax Tuner to write custom EFILive tunes for the potent combination. He estimates that the engine delivers 1,150 horsepower and 2,000 lb/ft of torque when maxed out, but the combination is still tame enough to be driven on a regular basis.

Engine components and brackets were powder coated bright maroon or metallic gray by Fox Valley Coatings to dress up the engine and engine bay. To make the outside of the truck look as good as the engine bay, Wehrli turned to the crew at KB Collision in Sugar Grove, Illinois. They added the cowl to the hood, removed the molding and badges, and installed a set of fender flares before treating the rocker panels to Rhino Lining. Once the body modifications were done and the body was smooth, they laid on several coats of PPG Story Gray paint giving the truck a flawless finish. To light the way at night he installed HID headlights and LED running light bulbs in addition to taillight housings from an ’06 model truck for a cleaner look.

Moving to the inside of the truck, you’ll find the original cloth factory interior that’s showing its age but is still in pretty good shape. To help Wehrli keep an eye on the performance of his highly modified Duramax engine. he relies on a total of six Auto Meter Cobalt gauges. He installed three boost gauges in a pod on the A-pillar to give him boost readings from each turbo. Then he installed a pyrometer in a pod on the steering column, and oil temperature and fuel pressure gauges in a pod above the rear view mirror. To make driving the truck even more entertaining, he installed a Pioneer touchscreen head unit in the factory location in the dash and installed a pair of 10-inch subwoofers under the rear seat.

Without a doubt, Wehrli has taken his first truck beyond his high school imagination as he developed his company alongside the big Chevy. Packing three turbos, three CP3s and well over 1,000 horsepower, this Duramax is a truck to be reckoned with. It represents his thriving diesel performance company well and he still uses it as a demo vehicle at shows and events as well as tearing up the track from time to time in brush pulls when there’s a class for him to hook. If you get a chance to check out the truck in person, it’s worth the time, as his attention to detail and amazing fabrication work shine even brighter up close and personal. DW