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Duralux: A Compound Turbo LML Denali HD

Running your own company can be a lot of hard work; countless hours and dollars are spent on research and development in hopes of building and selling products or services. Jason Wehrli owns Wehrli Custom Fabrication (WCFab) in Sugar Grove, Illinois, and has created some very cool parts and kits for diesel enthusiasts to upgrade their trucks. He purchased a used 2012 GMC to develop new parts for LML-equipped Duramax trucks, but rather than buying a run-of-the-mill truck he found a Denali HD and built from there. So we guess there are benefits that come along with all that hard work and running your own company too.

The Denali HD trucks are treated to a unique grille that’s bold, but it’s what’s hidden under the hood that makes this truck impressive.

Wehrli’s Denali HD crew cab truck was purchased with more than 15,000 miles on the odometer; it was fully loaded and in great shape. But as nice as the truck was, he purchased it as a research and development tool so immediately after the purchase it went under the knife. His top priority was to develop a compound turbo system for the LML that would work with the factory VGT turbo while delivering improved performance. An S475 would be paired with the factory turbo using fabricated plumbing on the exhaust and intake sides of the chargers.

Exhaust gasses exit the stock manifolds through a set of WCFab 2-inch stainless steel up-pipes before entering the factory charger and being handed off to the S475 through heat-wrapped piping. Then the new downpipe hands the spent gases off to a 4-inch diameter aFe exhaust system with a 6-inch tip that exits the truck in the factory location. On the intake side, a large aFe filter sends plenty of clean air to the S475 which compresses the charge and hands it back to the inlet of the factory charger. The outlet from the factory charger is then routed to and through the factory intercooler through WCFab 3-inch-diameter boost tubes. To make the system look as good as it performs, Wehrli had the cold side plumbing powder coated in bright metallic red to really pop under the hood.

The Wehrli Custom Fabrication compound turbo system is powder coated bright metallic red to really stand out when the hood is lifted.

The compound turbo kit Wehrli designed for the LML trucks allows both batteries to be retained in their original locations under the hood, making the system usable on daily driven trucks, even in cold climates where one battery may struggle to start the Duramax engine. A compact fabricated aluminum tank replaces the factory overflow tank. He opted to have the tank powder coated to match the turbo piping. Everything fits neatly under the original hood to keep the true potential hidden away from prying eyes, but when the hood is lifted, the powder coated parts and extra turbo charger really stand out and show that Wehrli is serious about his Duramax performance upgrades. While he has not dyno tested the Denali yet he estimates that the truck is putting down somewhere around 565 horsepower and about 1,000 lb/ft of torque.

Wehrli did make a slight modification to the interior of his Denali with a triple-gauge pod for the A-pillar and a trio of Auto Meter gauges to monitor boost of each turbo as well as exhaust gas temperature.
Wehrli uses an air bag-cushioned gooseneck mount with his B&W turnover gooseneck hitch to make towing safer and more comfortable.
Jason Wehrli developed his compound kit using the stock turbo along with a big S475 to make good power without crazy EGTs under heavy loads. The S475 turbo inhales fresh air through a large aFe air filter element.
Wehrli replaced the factory coolant overflow tank with this fabricated aluminum tank that’s powder coated to match the rest of the turbo system.
Stainless steel tie rod sleeves from Merchant Automotive are used to strengthen the steering system and prevent the truck from excessive toe-in under power or, worse yet, bent/broken tie rods that could lead to an accident.
The rear suspension of the Denali HD is totally stock, including the shocks and 3.73 gears. You can also see the 4-inch diameter aFe exhaust system that terminates in the factory position with a 6-inch diameter polished stainless steel tip.

Wehrli purchased the truck in July of 2013 and he was determined to have it on display with his new compound turbo kit at the 2013 Scheid Diesel Extravaganza in August. In addition to getting the truck done and ready for the big diesel event, he also had the added pressure of proving the performance of his products by using the Denali HD to tow his triple-turbo ’02 Chevy Duramax show truck to and from the event. To make that possible, he installed a B&W turnover gooseneck hitch mount below the bed and upgraded the rolling stock to 305/65R18 BFGoodrich All-Terrain T/A tires wrapped around 18×9-inch Eagle Alloy wheels. The truck was completed the day before loading up for the Extravaganza, then tuned by Duramax Tuner in Union, Illinois, and hooked to the gooseneck trailer for the drive to Terre Haute, Indiana, the next morning.

Wehrli installed a set of Cognito upper control arms to strengthen the front suspension and make sure it holds up under the increased power. Then addressing another IFS weak point, he installed a set of Merchant Automotive tie rod sleeves to prevent the dreaded Duramax IFS toe-in under power. The rest of the suspension and chassis under the Denali HD remains stock, including the factory differentials and 3.73 gearing. The Duramax is backed by a factory Allison transmission that’s been upgraded with a Sun Coast torque converter.

Cognito upper control arms provide more strength and better looks than the factory control arms.
Wehrli opted to mount his BFGoodrich All Terrains white letter out for a classic look but wrapped them around a modern 18-inch Eagle Alloy wheel.
Wehrli’s Denali HD sits at stock height, giving it a good stance with the larger wheels and tires, and making it a perfect research and development truck that pulls double duty as a tow rig.
Just one day after the compound turbo kit was installed on the Denali HD, Wehrli loaded up his 2002 Duramax truck and headed down to Terre Haute, Indiana, to enter both trucks in the show-n-shine.

Moving inside the truck you’ll find plush leather seating with a luxury feel thanks to the Denali HD trim package. Amenities like heated and air-conditioned seats, heated steering wheel, backup camera and Bose sound system leave little to be desired. Wehrli installed a triple gauge pod on the A-pillar with a trio of Auto Meter Ultra-Lite II gauges to monitor the boost of each turbo stage as well as to keep an eye on EGTs, making it much safer when towing heavy loads.

The Denali HD sports a luxurious interior with wood trim and a sleek design coupled with creature comforts like a heated steering wheel and leather seats that are both heated and cooled.
From any angle this is a great-looking daily driver truck and, with nearly 600 hp on tap, this is the view most other drivers will see.

The Denali HD may look complete but Wehrli isn’t finished yet. As a research and development truck, Wehrli will use it to continue to develop and refine performance products for the LML Duramax platform. We’ve heard that by the time you read this article the truck will have WCFab’s dual CP3 kit installed and there are more parts in the works as well. So keep an eye out for it at diesel events across the Midwest; you may see some of Wehrli Custom Fabrication’s latest parts. One thing is certain—the LML variety of Duramax engines can still be upgraded with performance parts and this Denali HD is proof that luxury can be teamed with performance and power! DW

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