An LML Built to Match its Owner’s Right Foot

When you crack a piston at 94,000 miles, you go all in. At least that’s what Garrett Zumwalt (@gzumwalt) did, a 21-year-old farmer from Silex, Missouri. With an ’05 LLY farmhand available for daily driving and towing duties, it only made sense for him to “officially” transform his ’14 Silverado into a full-time play toy. The LML Duramax is built about as well as you’d need for a truck that’s set up to send 800 to 1,000 hp to the pavement. A built Allison, a healthy fuel system, and an S400 play critical supporting roles in the effort, and the right traction and steering mods are in place, too.

No-Frills LML

After one of the LML’s eight original pistons bit the dust with nothing more than a tune for a power-adder, Garrett wanted to avoid any type of catastrophic engine failure going forward. Enlisting the help of LinCo Diesel Performance, and with LDP knowing Garrett to be (self-admittedly) a bit hard on things, a host of stronger hard parts were rounded up for the rebuild. Things got started with a factory stroke (3.900-inch) keyed Compstar crankshaft from Callies, with Wagler Competition Products’ billet main caps and ARP main studs securing it within the block. A set of Wagler’s forged-steel Street Fighter rods, complete with ARP rod bolts, attach to coated Fingers oval bowl pistons, and one of Wagler’s keyed Stage 2 alternate fire camshafts sits in place of the factory one. Up top, the heads were treated to a performance valve job at LDP Machine, along with Wagler dual valve springs and ARP 425 head studs.

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The LML Duramax in Garrett Zumwalt’s ’14 Silverado was pieced together at LinCo Diesel Performance, with a balanced rotating assembly that consists of a keyed Callies Compstar forged-steel crank, Wagler Street Fighter forged-steel rods with ARP rod bolts, Fingers oval bowl (and thermal coated) cast-aluminum pistons, a BD billet flexplate, and a Fluidampr. Wagler’s billet main caps and ARP main studs help anchor the Compstar in place. Valvetrain upgrades include a keyed Stage 2 alternate fire cam, dual valve springs, and chromoly pushrods from Wagler, while ARP 425 head studs hold down the fort.
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Sitting atop the built 6.6L is a single S400 system from HSP Diesel, complete with an S468 from Stainless Diesel. The T4 charger’s compressor side features a billet, 5-blade 68mm (inducer) wheel and a V-band outlet, with an 83mm turbine wheel sitting on the opposite end of the shaft, within a 1.0 A/R exhaust housing. The 5-blade S400 comes to life quickly thanks to the combination of a Stainless Diesel turbo blanket, PPE high-flow exhaust manifolds and stainless up-pipes, a high-stall converter, and sound tuning. Under load, the S468 knocks on the door of producing 50 psi of boost.

CP3 Swap & 45-Percent Overs

For utmost reliability, the factory Bosch CP4.2 was done away with. A CP3 conversion kit from Fleece Performance Engineering made the CP3 swap possible, and Garrett opted for Fleece’s PowerFlo 750. The 10mm stroker pump has no issue maintaining rail pressure for the 45-percent over Exergy Performance injectors, even with significant duration brought into the mix. Low-pressure fuel supply is delivered to the CP3 through ½-inch lines spanning to a 165-gph Titanium series FASS system. A drivable, 800 hp is made possible thanks to Danville Performance tying everything together in the LML’s ECM.

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Efficient power transfer and the ability to stand up to more than 1,500 lb-ft of torque begins with a Stage 5 competition Allison from LinCo Diesel Performance. The six-speed auto was treated to Xcalliber billet input, intermediate, and output shafts, along with a billet 6-pinion P2 planetary and C2 hub from Sun Coast. A mixture of Sun Coast’s SCZ clutches also made the cut, with one of the company’s 1055-2 triple disc converter’s sitting on the input shaft. The 2,400 to 2,600-rpm stall converter works flawlessly with the S400 and a Fleece AlliLocker gives Garrett complete control over lockup.
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A 165-gph Titanium Series fuel system from FASS pulls diesel from the factory tank and sends it toward the high-pressure pump. In this case, the CP4.2 has been replaced with a 10mm PowerFlo 750 CP3 from Fleece Performance Engineering, and made possible thanks to the company’s CP3 conversion kit. The injectors came from Exergy Performance, where the balanced piezo units were fitted with 45-percent over nozzles. As you read this, Garrett has likely already upgraded to a 14mm CP3 and 150-percent over injectors in his bid to break 1,000 rwhp.
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Instances of toe-in are completely eliminated thanks to a set of PPE’s burly tie-rods. The Stage 3 units are forged, 1.5-inches wide, and incorporate 2-1/3-inch ball joints. For a truck owner like Garrett, who thoroughly enjoys his boosted four-wheel drive launches, these tie-rod assemblies are the cat’s meow in the diesel industry.

VGT Delete

Even though he ran a 63mm VGT for a time, uncorking the LML’s true potential meant switching to a bigger, fixed geometry charger. The ideal turbo would come from Stainless Diesel: a 5-blade S468/83/1.0 with a V-band compressor housing outlet and a T4 turbine inlet flange. HSP Diesel supplied the single S400 system, complete with a pedestal, 3-inch diameter intercooler piping, and even the cold air intake. Helping to drive the S400 is a set of PPE’s high-flow exhaust manifolds and stainless steel up-pipes. The 5-blade S400 sends just under 50-psi of boost through the factory intercooler.

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To quell axle wrap, a set of traction bars sourced from LinCo Diesel Performance keep the rear AAM 1150 and its suspension happy. The simple yet effective bars make use of weld-on frame brackets, with bolt-on brackets at the axle tubes. Garrett also replaced the factory aluminum driveshaft with a steel one, which will come in handy this summer when he hooks to the sled.

All-Billet Allison

Built with plenty of insurance for Garrett’s current horsepower combination, the Stage 5 competition Allison 1000 was assembled at LinCo Diesel Performance. The six-speed benefits from LinCo’s proprietary clutch kit made up of a mixture of Sun Coast SCZ clutches. Billet hard parts include Xcalliber billet input, intermediate, and output shafts, along with Sun Coast’s billet C2 hub and P2 planetary. To bring the S468 to life quickly, a 1055-2, high-stall (2,400 to 2,600 rpm) triple-disc Sun Coast converter is employed, while a Fleece AlliLocker provides full control over lockup.

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Having good drivability along with solid horsepower begins with superior tuning, so Danville Performance got the call when it was time to dial-in the well-fueled, single S400 LML. Calibrated with EFILive, Garrett navigates his files by way of a DSP5 switch mounted next to the factory trailer brake controller.
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The latest parameter monitoring device on the market, Edge Products’ Insight CTS3, allows Garrett to keep an eye on key vitals. Rail pressure, boost, transmission temp, and engine coolant temp are among his list of essentials present on the 5-inch HD screen.
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Nitto Ridge Grappler (we’re told he’s got a fresh set now). The hybrid terrains (a mix of all-and-mud terrains) meaasure 33×12.50R20, and accommodate 20×10 Hostile Jigsaw wheels. Flashy but not over the top, this wheel and tire combo allows his 800hp Bow Tie to fly under the radar.

Never Satisfied

A horsepower junkie to the core, right about the time Garrett’s truck clears 800 hp on the chassis dyno he plans to tear into the engine again, add 150-percent over injectors, a 14mm CP3, a bigger S400, and pursue four-digit horsepower. With plans to hit a few Midnight Madness events at the local quarter-mile—along with hooking it to the sled—this summer, you’ll either find Garrett putting the truck’s driveline to the test in the dirt, or somewhere in the 11’s at the drag strip.

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