The story behind Neal Driedger’s 2019 GMC—the most powerful factory sealed L5P Duramax in the world.
Thanks to stronger pistons, larger rod bearings, and higher flowing heads, the L5P Duramax has proven extremely durable and powerful with added fuel and air in the mix. Back in the spring, All In Truck Performance’s Neal Driedger decided to find out just how tough the 48,000-mile L5P in his 2019 GMC Sierra 2500 HD was. Already making a dyno-verified 1,156 hp on fuel courtesy of big compounds, plenty of fuel, and a built Allison 1000, Neal and his co-workers (cohorts?) decided to throw larger injectors, a different tune-up, and a boatload of nitrous at the factory-sealed Duramax…
It responded by making 1,579 hp and 1,993 lb-ft of torque—a new world record for a factory long block L5P Duramax. For a closer look at this big boost, stock hard-part monstrosity, we met up with Neal and his GMC at the Ultimate Callout Challenge, where it had just turned in a repeat performance of 1,516 hp and 1,931 lb-ft on the rollers. The late-model Duramax wasn’t so lucky this time, but its owner—undeterred by the damage—was under no illusions it would last forever at that power level. There are those that push the limits and there are those that don’t care if they find them. Neal Driedger is the latter diesel owner, and this is his story.
Here it is. The dyno graph that broke the Internet back in May. Fine-tuned in-house at All In Truck Performance, you can see that the horsepower and torque curves all but mirror each other. Waiting until higher rpm to pour on the fuel is a textbook way of keeping rod-bending cylinder pressure (i.e. torque) at bay and preserving the life of an engine. We’ll also note that thanks to having no rpm limiter in place, Neal’s L5P can turn more than 4,000 rpm—a feat that the L5P’s LS-like roller lifters and beehive valvesprings appear to be designed for, and that could help him find even more horsepower with bigger compounds in the mix.Why play with fire by running a set of compound turbos on a stock bottom end, you ask? For starters, Neal’s GMC is his tow-rig (yes, a tow-rig), so while a big single charger would’ve been much safer on factory internals it wouldn’t have been practical with a trailer in tow. The L5P Duramax that lies beneath these chargers and their respective piping has never been opened up. In fact, not even the OEM head bolts have been swapped out for studs. Neal’s daily drivable, 2,000 lb-ft adventure has proven a true testament to just how robust the L5P platform is.With help from Wehrli Custom Fabrication, the compound system combines a pair of sizable S400s from Turbo Diesels Inc. (TDI). The atmosphere charger, an S494, makes use of a billet 94mm compressor wheel, a 111mm turbine wheel, and a loose, T-6 divided 1.45 A/R exhaust housing. In the valley, an S472 brings things to life. It sports a billet 72mm compressor wheel, a 93mm turbine wheel, and a T-4 divided 1.00 A/R exhaust housing. Taking advantage of the L5P’s ability to turn more than 4,000 rpm, Neal’s truck makes big power between 4,000 and 4,500 rpm. Perfect for a set of high-flow compounds.Big boost had to be matched with big fuel in order to get the truck to this power level (even before an open -6 AN nitrous line entered the chat). To get there, Neal went with the largest Denso-based off-the-shelf injectors Exergy Performance offers, a built-to-order set equipped with 200-percent over nozzles. Before the injectors perform their in-cylinder magic, a 14mm stroker CP3 (also from Exergy) supplies them with ample rail pressure, sometimes as high as 36,000 psi. On the inboard side of the driver side frame rail, just ahead of the factory tank, a 220-gph AirDog II-5G low-pressure fuel supply system kick starts the horsepower-making process.Surprisingly, the six-speed Allison 1000 handles the truck’s 2,000 lb-ft without any billet shafts or planetaries (Neal told us it was built when the truck was making less power). Assembled using a recipe the folks at All In Truck Performance have found to work best for higher horsepower customers, Neal’s transmission features a mix of Raybestos and Alto clutches, a billet stator and triple-disc “R stall speed” torque converter from Goerend Transmission, and one of Goerend’s cast-aluminum deep pans. A BT DieselWorks lockup controller allows Neal to override the TCM and manually lock the converter.Strapped to the SuperFlow chassis dyno at All In Truck Performance, Neal’s GMC made an impressive 1,257 hp and 1,637 lb-ft on fuel. Then came the ghetto fogging that added another 322 hp and 356 lb-ft. For the show he put on at U.C.C., Neal rigged up a -6 AN line running straight to the truck’s airbox. The flow of N2O was controlled via the ball valve pictured here. If you’re going to ghetto fog an engine, this sure beats standing beside a turbo that’s on the verge of overspeeding with a bottle of highly pressurized gas in your hands.If you’re going to own a record, the truck that sets it better look the part, right? Neal’s bad black Sierra gets it done thanks to a set of 24×11-inch FF119 Cipher wheels from Fuel Off-Road. The mirror-polished, forged-aluminum rims boast a 0mm offset, which keeps them from sticking out too far (something Neal isn’t a fan of). They’re wrapped in 305/35R24 Toyo Proxes ST III tread, and the-all season tires do all they can to hold the road when Neal’s right foot gets heavy.It’s a tough job, but somebody’s traction bars have to do it. These CalTracs from Calvert Racing have the task of keeping the GMC’s AAM 1150 rear axle from wrapping under 1,900-plus lb-ft of torque. These bars have long-been one of the most effective, low-profile ways to control leaf spring wrap, eliminate wheel hop, and maintain rear pinion angle on diesel trucks. And even though Neal doesn’t drag race his Sierra anymore, the CalTracs aid its towing efforts by keeping the pinion angle from lurching downward during braking. Of course, they also come in handy on all of those 1,500hp dyno hits.It’s been a minute since Neal’s GMC has been to the drag strip, but once upon a time (and about 700 hp ago) it went 11.80s in the quarter-mile. Should Neal choose to get back on the track at some point, he’ll put the truck’s center link steering stabilizer bracket from DHD to good use. During boosted, four-wheel drive launches, it transfers all the load away from the center link and eliminates the toe-in issues IFS-equipped GM’s often experience under big power. In the looks department, we appreciate the way Neal’s classic black silver specialty license plates tie in with the truck’s black-on-chrome theme.Less than two weeks after his 1,579 hp and 1,993 lb-ft numbers shocked the world, Neal hauled his L5P 1,200 miles to Indianapolis to try his hand on the Northwest Dyno Series / Ultimate Callout Challenge dyno—the same model SuperFlow he uses back home. Unfortunately, during the meat of the run Neal forgot to manually force the converter to lock up, it unlocked, the engine spiked to 5,200 rpm, and the Duramax lifted a head. However, right before all of it happened the truck cleared 1,516 hp and 1,931 lb-ft on the rollers, backing up the numbers he’d made back in Texas.The severity of the head gasket failure allowed coolant to exit the exhaust as well as hydrolock the engine. And while the results of the all-out head gasket failure weren’t pretty, they weren’t catastrophic either. This is the kind of shape the passenger side cylinder head was in on cylinder number 1, and even though a pair of rods were shortened during the high-horsepower melee, all eight pistons were unscathed. It’s all the confirmation we need that the L5P Duramax is the stoutest 6.6L diesel V-8 General Motors has ever produced.If anyone thought the carnage incurred at U.C.C. was going to force Neal to back off the throttle, they were sorely mistaken. Quite the opposite, he’s gone full steam ahead, already having sourced a 15,000-mile takeout engine and stuffed it into his Sierra. This time, the heads are anchored to the block with ARP studs, the oil pump has been pinned to keep the gear from spinning on the shaft at high rpm, and Wehrli Custom Fabrication’s high-flow, billet exhaust manifolds and 2-inch stainless steel up-pipes are in place. With the new stock bottom end L5P Duramax prepped to handle even more abuse, we expect Neal to push the factory hard parts even further this time.
