Meet Big Blue, an '03 GMC Sierra 2500 HD powered by General Motors' Duramax 6600 diesel V-8. Used by GMC and Chevrolet in its heavy-duty pickups, the Duramax has only been available since 2001, but in four years, it's been a smashing success, taking GM's light truck diesel business from about 1 percent market share to just less than 30 percent.
Such success comes from equiping trucks with contemporary, light-truck diesel technology like four-valve-per-cylinder aluminum cylinder heads; roller lifter camshafts; high-pressure, common-rail direct injection; variable nozzle turbochargers; cooled exhaust gas recirculation; and finally electronic engine controls. Bolstering the Duramax's new popularity is good performance: 300 hp-the '05-and-later models will feature 310 hp-and 520 lb-ft torque ('05-and-later automatics will feature 605). The Duramax was engineered jointly by Isuzu and GM's Powertrain Division and is manufactured at General Motors' Moraine, Ohio, plant.
Big Blue is a work truck owned by Gary Peterson who is in the concrete surface preparation business. He uses his GMC to pull a trailer that hauls a big, shot blasting machine, tools, and bags of steel shot.
Bottom line, Gary wanted more power from his Duramax, and we were looking for a project truck.
Baseline TestsFirst, we took this GMC to Westech, a test facility in Mira Loma, California, that is co-owned by John Baechtel and specializes in engine and chassis dynamometer testing.
Westech's SuperFlow SF-840 can be run either as an inertia dyno or an eddy current brake dyno. For our baseline, test operator Tom Habrzyk ran it in the inertia mode and made two nearly identical runs that averaged 257.6 hp at 3,069 rpm and 482 lb-ft torque at 2,285 rpm at the rear wheels, corrected to the SAE standard. Considering Duramaxes are rated at 300 hp and 520 lb-ft torque, either this 36,000-mile, stock truck has unusually low driveline loss, which is unlikely, or the engine is performing better than rated.
We installed a Vericom Performance Computer in Big Blue and did some acceleration tests. We ran an average 0-60 time of 8.98 seconds and an average quarter mile performance of 16.93 seconds at 82 mph.
Gauging Heat and PressureWith the high-performance tuning of diesels, exhaust gas temperature (EGT) is a key issue. Generally, the hotter the exhaust, the more powerful the engine, but with a turbo-supercharged diesel, EGT has a limit, if acceptable durability is desired.