Chevrolet and GMC have brought the competition to Ram and Ford trucks by offering up a new 6.6-litre Duramax diesel capable of producing 445 horsepower and 910 lb-ft of torque in their Silverado and Sierra HD pickups, respectively.
The all-new Duramax diesel shares its bore and stroke dimensions and thus its displacement with its predecessor, but the engine has been reworked from oil pan-to-cylinder head, the automakers said late September; it will be available in Chevy’s 2017 Silverado HD and GMC’s 2017 Sierra HD.
A new GM-developed control system helps the diesel produce 90 percent of its peak torque from 1,550 rpm, maintaining this plateau of twist up to 2,850 rpm—relatively high-rpm for a diesel.
General Motors has used aluminium extensively throughout the engine, constructing the cylinder head and pistons from the light-weight alloy to reduce overall weight.
Among a plethora of other updates, the new Duramax features an upgraded common-rail fuel injection system that can pressurize the diesel up to 29,000 psi (2,000 bar) for excellent atomization of the fuel and complete, clean combustion.
Other upgrades include a new electronically controlled, variable-vane turbocharger capable of up to 28-psi (195 kPa) of boost; a new cooling system that incorporates a new double-layer water core design into the head casting, thereby extracting heat more evenly and efficiently; and new microprocessor-controlled glow plugs capable of starting up the engine in fewer than three seconds in temperatures as low as -29 C, without a block heater.
“Nearly everything about the Duramax is new, designed to produce more torque at lower rpm and more confidence when trailering or hauling,” said Gary Arvan, chief Duramax engineer.
“You’ll also notice the refinement improvements the moment you start the engine, and appreciate them as you cruise quietly down the highway—with or without a trailer.”
While the new 6.6-litre Duramax packs a seriously torque-y punch, it is still bested by Ford’s 6.7-litre Power-Stroke diesel, which produces a best-in-class torque figure of 925 lb-ft; Ram’s 6.7-litre Cummins diesel trails its competitors with 900 lb-ft of torque, though Ram continues to offer best-in-class towing capacity, at 14,157 kilograms (31,210 lb) in 3500 trim.