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2004 GMC Sierra Denali Turbo - Street Sleeper

A Wolf In Sheep's Clothing

Brandan Gillogly
Aug 1, 2008
Photographers: Bob Ryder
Photo 2/10   |   2004 Gmc Sierra Denali Turbo left Front Angle
This is our horsepower issue, so we'd be remiss not to give you feature trucks that can hold their own against a muscle car. That's exactly what Mark Helmandollar set out to do with his truck. At first glance, Mark's '04 GMC Denali looks like just an ordinary, clean, mild custom that you'd see doing any number of everyday chores. But looks can be deceiving.
Mark first test-drove a Sierra Denali in 2002, when Quadrasteer first became an option. He loved the ride and handling from the all-wheel-steering and all-wheel-drive, but couldn't budget the $50,000 asking price. Mark test-drove more new Denalis over the next three years, but it wasn't until 2005 that he was able to find a pristine '04 model, the last year with Quadrasteer, for a good price. Soon afterward, Mark found himself spending a lot of time on and, soaking up the information on how to make his truck faster. The first big step was adding a Radix supercharger and a built 4L65E transmission. A few additional mods had Mark running 12.8 in the quarter. Not bad for a 6,300-pound truck. Soon after, a Belltech 2/4 drop kit with spindles and shocks was bolted on with 20-inch Driv Moonshine wheels and 285/50R20 Toyo Proxes. The additional weight of the wheels and tires dropped Mark back into the 13s in the quarter, so he was on the lookout for more power.
Photo 3/10   |   Drawing even more attention to the twin turbos, the red powdercoating looks like a candy paintjob and matches the red anodized TiAL 44mm wastegates.
Still waiting for his answer, Mark focused on the aspects of the truck that he could upgrade. The bed got a Rollbak tonneau, while the front end received HIDs with clear corners and a billet grille emblem. Inside the truck, it's still mostly stock, but a Denali already came with heated leather seats and navigation, so stock wasn't all that bad. One noticeable change is a set of pillar-mounted gauges that monitor air/fuel ratio. That gauge would definitely come in handy later.
In April of '07, GM released the LSX block and Mark's prayers were answered. Mark had done his homework and knew to call Synergy Motorsports in Newark, California. Rick Hollenback, the owner of Synergy Motorsports, helped Mark get all of the parts necessary to meet his goal of extreme horsepower. The LSX block was bored to 4.175 inches to fit custom Diamond pistons and Callies Compustar 6.1-inch rods and 4-inch stroke crank. That works out to 438 ci, which would have been a whole lot of fun with the Radix supercharger that Mark already had, but the iron block can handle some serious boost, so the guys decided to really turn up the pressure with Synergy Motorsport's twin turbo kit.
Photo 4/10   |   2004 Gmc Sierra Denali Turbo engine
Air is drawn into the two Garrett GT35R turbos through conical K&N filters and ductwork powdercoated red by Maas Brothers powdercoating in Livermore, California. The boosted air is then routed through a custom intercooler and is sprayed with methanol from an Alkycontrol super pump system to reduce the possibility of detonation. The truck's cooling system was also upgraded to reduce detonation by adding Evans Cooling Systems waterless coolant.
The air/alcohol mixture is then fed through an L76 intake and into the cylinders via L92 heads and a custom ground Synergy cam with .620 inches of lift. The L76/L92 combo is what you'd find on an LS3, but for Mark's application they were given a Stage 2 porting job, dual valve springs, and Harland Sharp roller rocker bearings by West Coast Cylinder Heads. Mark has big plans for the engine, so two Bosch 420 fuel pumps were added to keep the 96 lb per hour injectors fed when the throttle is pegged. When Mark finally eases back on the throttle, a Vortech Mondo blow-off valve keeps the turbos from surging.
The power and torque this engine is capable of making would have demolished most transmissions, so Chuck and Vince at Finishline Transmission built a 4L80E with billet input and main shafts and a 10-1/2-inch, 2,600-2,800rpm stall torque converter. South Bay Driveline built a 4-inch-diameter steel driveshaft to get the power to the Quadrasteer rear end, with two driveshaft hoops along the way. So far, the driveshaft hoops have proven to be nothing more than insurance, but with diesel-like torque on demand, it's peace of mind for Mark when he's running on the street, as well as on the track.
Freshly assembled and with only 50 miles on the clock, Synergy strapped the truck down to its all-wheel-drive dyno. Running a modest 12 pounds of boost and with a conservative rich air/fuel mix, the truck put down 712 hp and 785lb-ft of torque, the next run netted 730 hp and 805 lb-ft. Once the engine is broken in and the real tuning happens, Mark is looking to crank up the boost to get 1,000 hp. So, if you ever find yourself in California's Bay Area, don't assume the Denali cruising next to you on the highway is a weekend toy hauler. Mark's Denali should be one of the quickest street-driven extended cabs out there, and with 18 psi of boost on the horizon, he's set the bar high for his competitors.
Mark would like to send special thanks to all of his friends and the people who helped make his dream truck a reality: Butch, Christopher, Richard, Chuck, Vince, Rick Hallenback, Shannon Robb, Jerry Burdick, Robert Corrigan, and Dave Lamanno.


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