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2004 GMC Sierra 2500 HD: Rock-Solid Sierra

A Full-Pulling, 12-Second Duramax

Mike McGlothlin
Nov 1, 2012
Photographers: Mike McGlothlin
Imagine you could build a Duramax that lived on the brink of destruction yet was indestructible. Somehow, we found just that in Andrew Karker’s ’04 GMC Sierra 2500 HD. Even when producing more than 600 rwhp, the 150,000-mile stock-bottom-end LB7 survives, and the truck consistently places toward the top at competitive sled pulls.
Photo 2/13   |   rock Solid Sierra gmc 2500 Burnout
So how does a 7,000-pound Work Stock truck stay ahead of 8,000-pound trucks making 700 hp or more? The answer is all the right parts in all the right places. Throughout eight years of ownership and five years of sled pulling, Andrew has addressed virtually every known weak link and put together a rock-solid combination.
Bulletproofing the AAM 925-based independent front suspension steering system called for upgraded tie rods, a straight centerlink, and pitman and idler arm braces. To make sure both front tires would share the workload, an Eaton ELocker was added. A polyurethane transmission mount and rear housing brace keeps the Allison 1000 and NV263 transfer case stationary and the driveshafts from seeing odd angles. At the rear of the truck, long, gusseted traction bars make axlewrap non-existent; 30-spline, non-tapered axleshafts keep the AAM 1150 alive; and adjustable bumpstops block suspension travel.
Photo 3/13   |   rock Solid Sierra gmc 2500 Front Three Quarter
How He Keeps The Bone-Stock Long-Block From Blowing Up
Aside from a set of ARP head studs, the long-block is 100 percent stock. The real power-adders come from a set of injector nozzles flowing 45 percent more fuel, a CP3 from Industrial Injection cranking out 85 percent more fuel, and EFILive tuning courtesy of Duramax-Tuner. A 150-gph FASS lift pump with a 10-micron filter sends fuel to the engine.
Photo 4/13   |   As you may or may not know, there’s a lot more to sled pulling than simply making horsepower—and every time Andrew’s truck hits the dirt, he proves it. His fine-tuned suspension and rigid driveline parts allow him to finish ahead of trucks making in excess of 700 hp—and trucks that outweigh his by 1,000 pounds.
Due to a stock-appearing turbo rule in his local Work Stock class, Andrew turned to River City Diesel, which all but reinvented the aftermarket version of the IHI turbo found on ’01 to ’04 Duramax engines. Called its LB66, the charger features a redesigned journal bearing centersection and a 66mm billet compressor wheel yet retains the factory compressor and turbine housings.
Freeing up airflow restrictions is a larger intake horn, a 3-inch intake Y, and a K&N cold-air system with an AFE dry filter. To keep EGT cool, the factory intercooler was ditched in favor of a Banks Techni-Cooler system. Less restriction on the exhaust side begins with an LML manifold on the driver side (the updated LML unit isn’t as crimped down in the steering shaft area as previous versions). Post turbo, a 3-inch MBRP downpipe bolts to a 5-inch exhaust section, which transitions into a 7-inch stack in the bed.
As you can imagine, once Andrew’s sled pulling addiction turned serious, the factory Allison 1000 was on borrowed time. So it was fortified using PPE’s Stage 5 rebuild kit, which includes upgraded C1 through C5 clutch packs. A River City Diesel torque converter sends power through the five-speed automatic.
At the truck’s current power level, Andrew knows he’s testing the limits of the stock LB7 connecting rods. But running at the top of a Work Stock class in the Midwest all but requires a complete engine build—or pushing the limits of the factory hardware. So far it’s paid off, as Andrew rarely finds himself finishing outside the top five at any given pull. Thanks to the reinforced suspension and bulletproof driveline, every ounce of the ragged-edge LB7’s power makes it to the ground. If Andrew’s GMC proves anything, it’s that you don’t have to light up the dyno to win in the dirt—or run a 12.0 in the quarter-mile.


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