2003 GMC Sierra 2500 HD - Big Power

  |   gmc 25000 front View Welcome back to our series on Big Blue, a modified, Duramax 6600-powered, GMC 2500HD. In Part One, we installed an Auto Meter Dual-A-Pillar pyrometer and boost gauge kit to measure a key, turbocharged diesel tuning factor: turbine inlet temperature. We put the pyrometer's sensor in an exhaust manifold because it was too difficult to tear apart the exhaust to weld a sensor bung at the turbo inlet. Later, we decided the pyrometer would be more accurate with the sensor closer to the turbo. It was no easy job, but removal of the left inner fender and a power steering pipe frame bracket, temporary bending of steering and brake pipes, and plenty of patience had us removing the pipe between the left manifold and the turbo inlet We reinstalled the bung-equipped pipe with new gaskets, moved the sensor, plugged the hole in the manifold, and rerouted the wiring. Pyrometer readings from the turbine inlet were, now, about 100 degrees Fahrenheit less, and our tuning was much more precise More Power
Next, was an ECM programming update from Ron Zimmer over at Z-Industries, the engine controls specialist discussed in Part Two. Ron's first effort knocked a whopping 1.1 seconds off Big Blue's quarter-mile time. For this issue of Diesel Power, we, again, installed our Vericom VC2000 Performance Computer in the truck and went testing. The latest Z-I calibration shaved another four tenths off the e.t., and driveablity improved as well. Our performance averaged 15.40 seconds and 93.9 mph, compared to our baseline from Part One of 16.93/82.0. We think Z-Industries does some of the best Dmax reprogramming work in the industry Still More Power
To date, performance enhancements have been: a Flowmaster American Thunder exhaust system, a Green Filter in the stock air filter assembly, Ron Zimmer's calibration work, and Red Line Synthetic lubricants. The American Thunder exhaust we installed in Part One comes with a racing downpipe to replace the catalytic converter. Cat removal is illegal for the street but is of interest, considering the number of Diesel Power readers who drag race. With the Flowmaster downpipe in place, a catless Big Blue was another 0.18 seconds quicker and 1.5 mph faster (15.22/95.4) on the drag strip. In addition, we noticed better response as the turbo was spooling up more quickly. The truck was also more consistent leaving the starting line. We suspect cat removal allows the turbo to build boost in a more controllable manner. What about the aftermarket intake systems, such as airboxes, which are popular with truck enthusiasts? We tested two airboxes for the Duramax on Big Blue. In repeated drag strip tests with street miles in between, both were responsible for slight decreases in performance. We reinstalled the stock airbox with the Green Filter and stuck with that. The O.E. air filter assembly and intake duct is a good design for a Dmax modified to the level of that in Big Blue. Faster (and Safer) on the DirtBig Blue racks up 4,100 miles a month in California and Nevada, going to construction projects. Some are accessible only on dirt or gravel roads. Time is money, so our hot rod Duramax gets driven pretty fast off road. A bad part of that is flying dirt, gravel, and stone chips sandblasting the headlights. To improve lighting performance and safety, we replaced the lights then added a set of WeatherTech LampGuards, 40-mil, clear, adhesive-backed, polyurethane overlays. LampGuards reduce abrasion and pitting. We also installed WeatherTech Side Window Deflectors which reduce wind noise and dust entry when the windows are down. Molded from 3mm lightly tinted, acrylic plastic, they fit our GMC perfectly. We couldn't resist one other WeatherTech product, FloorLiner, which completely covers the carpet in the footwells Another part of Big Blue's undesirable performance on dirt and gravel roads is poor traction-understandable considering the truck's stock, Bridgestone, LT245/75R16E, on-road tires. We needed more traction on unimproved roads. For increased performance, we looked to Goodyear, the last big American tire company, which recently introduced the Wrangler featuring Silent-Armor Technology, a new, on- and off-road tire. As Covina, California, Goodyear dealer, Tucker Tire Sales, explained, "Silent Armors have a quieter tread design, a layer of nearly indestructable Kevlar, and the Durawall puncture-resistant sidewall Goodyear uses in its extreme off-road tire, the MT/R, and Rim Guard, originally developed for ultra-performance car tires, such as the Eagle F1 GS-D3, which protects wheels from curb impacts In the quest for traction and looks, we also, went to a wider LT285/75R16D. While those are load range D, and the tires we removed were Es, because the larger 285 supports more weight, we don't believe there will be a performance or safety problem when the truck is loaded to GVW. Bigger tires need wider wheels, so we added a set of 16x8-inch Weld EVO Cheyenne 8s. Cheyennes are pretty light at 22.5 pounds each, compared to cast-aluminum wheels of the same size. We need all the help we can get because as good a tire as the Wrangler is if you go to a 285/75 from a 245/75, you get more weight. While tire/wheel weights bulked up from 55.5 to 86 pounds each, it could have been worse had we not used EVO Cheyennes. We tossed the Welds and Goodyears in the back of Big Blue and headed for Tucker Tire's nearby service facility for mounting, balancing, and installation. Leaving Tucker, we didn't drive far before we noticed, in spite of a more blocky, aggressive tread, the Wrangler Silent Armors are no louder than the highway tires we took off. Once we tried our 2500HD on some dirt roads, the difference in performance was immediately obvious. The Wranglers' more aggressive, on/off-road tread really bites on dirt and gravel roads Final Actions
Going to a tire that performs better on unimproved roads and significantly enhances appearance forces a trade-off. With the Goodyears and the Weld EVO Cheyennes on the truck, we, again, tested with our VC2000. Big Blue went 15.50 seconds and 92 mph, 0.29 seconds off our previous best. We took an e.t. hit because the 2.3-inch taller tires were like going from the stock, 3.73 rear end to a 3.42. If we do more to Big Blue, we'll change the ratio to 4.10, which should get us back in the low-15s, while maintaining better performance on gravel roads Our modified Duramax is quicker. In Part Two, it performed better on the chassis dyno. Big Blue's owner, Gary Peterson, reports that over the last six months, in 25,000 miles of work-truck duty, the fuel mileage picked up about 1-1/2 mpg.