2004 GMC Sierra Denali Turbo - Street Sleeper

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 performancetrucks.net and silveradoss.com, 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.

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.