GMC adds a heavy-duty truck to its off-road-ready lineup with the ’17 Sierra HD All Terrain X powered by General Motors’ fifth-generation 6.6L Duramax turbodiesel V-8.
Unveiled at a media event in Austin, TX, the trail-ready crew cab 4x4 joins the Canyon and light-duty Sierra 1500 in the brand’s All Terrain X portfolio.
The monochromatic All Terrain X package includes 18-in. black-painted aluminum wheels shod with Goodyear Duratrac off-road tires, Z71 off-road suspension, underbody skid shield and an Eaton locking rear differential. The truck is offered in Black Onyx or Summit White.
“The new Sierra HD All Terrain X’s powerful attitude reflects a popular trend in very capable off-road trucks, executed with a range-topping level of refinement – a combination of attributes GMC has cultivated for years,” says Duncan Aldred, vice president-GMC Sales and Marketing. “And with the new, available Duramax 6.6L, this truck more than matches its bold good looks with true professional-grade capability.”
Terrain X buyers choose between the all-new Duramax or a 6.0L gasoline V-8 also offered on the Chevrolet Silverado HD. The Duramax, codenamed L5P, delivers 445 hp and 910 lb.-ft. (1,234 Nm) of torque, up 13% and 19%, respectively, from 397 hp and 765 lb.-ft. (1,037 Nm) in the fourth-generation LML Duramax.
Gary Arvan, chief engineer and program manager for the Duramax HD diesel, says although the engine remains a 90-degree V-8 with the same bore and stroke (103 mm x 99 mm), valvetrain architecture and cast-iron block with aluminum heads, 90% of the L5P part numbers are new and the entire structure and block is upgraded to handle a 20% increase in cylinder pressure to 2,611 psi (180 bar).
New are the cylinder heads, crankshaft, pistons, piston pins and connecting rods, with attention to better cooling, reduced friction and better load-bearing capabilities. The engine gets a new turbocharger, an upgraded fuel system, intake port revisions, high-temperature exhaust manifolds and improved air flow to enhance performance.
A heavy-duty oil separator captures engine oil from blow-by gases and uses turbo boost pressure to return the oil to the crankcase under heavy loads.
A unique air intake system uses a new hood scoop in addition to a fender-mounted air scoop to bring in cool air to keep intake temperatures down, enabling improved engine performance especially under heavy loads, says Tom Dye, lead development engineer.
Dye says the hood scoop required special attention to prevent rain water from entering the intake manifold and harming engine performance. To prevent water from getting in, engineers devised air-intake piping that makes several sharp turns and expands, changing air pressure so that moisture drops out into a collector before the cool, dry air reaches the intake manifold.
Brief test drives of a ’17 Silverado HD equipped with the new Duramax engine reveal substantial power, with strong pull available from as low as 1,550 rpm. GM says the engine improvements result in a 0.7-second reduction in 0-60 mph (97 km/h) time to 7.1 seconds, as well as better response in 50-70 mph (80-113 km/h) acceleration.
The engine also is 38% quieter at idle than its predecessor and boasts a 35% reduction in emissions, GM says.
The new Duramax is produced at GM’s Moraine, OH, plant. The ’17 heavy-duty pickups go on sale in early 2017.
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