The Duramax name is about the only thing that GM's new ultra-efficient diesel engine, in final phases of development, shares with the current iteration. The diesel currently sold under the hoods of Chevy Silverado and GMC Sierra trucks (the hybrid version's shown above) is a 6.6-liter torque monster co-developed with Isuzu back at the turn of the millennium. Expected the new Duramax to produce in excess of 310 horsepower and 520 pound-feet of torque, coming mighty close to the prodigious output of the current version (365 hp, 660 pound-feet) despite a displacement smaller by 2.1 liters. Of note, GM engineers developed this new Duramax entirely in house, throwing out all assumptions and preconceived notions about diesel engine design.
GM says it will use this new diesel in its Silverado and Sierra half-ton pickups built after 2009, as well as the HUMMER H2 should that brand still be in the corporate fold upon the engine's release (doubtful: "Last HUMMER Dealer in Vegas Shuttered"). Very clever packaging allows the entire unit, turbo/intercooler and all, to fit in the same space as a GM small-block V-8, an engine known for its tidy packaging. This should make it applicable not only to trucks but to other rear-wheel-drive vehicles in the General's stable (diesel Camaro, anyone?).
Remarkably, the engine does not have traditional intake manifolds, and the exhaust manifolds spill into the 72-degree V-bank between the cylinder heads where a variable-vane turbo is also conveniently located for quick spooling and minimal heat loss. The pressurized intake charge is fed right through the valve covers via trick ports that we can't wait to see illustrated in detail. In another change from the current Duramax that uses pushrods for valve actuation, the new engine's four valves per cylinder will be activated by dual overhead camshafts.
It all adds up to fuel efficiency gains of 25 percent, a CO2 emissions reduction of 13 percent, and particulate and NOx reductions of over 90 percent when compared to GM's current diesel trucks. The engine will be built at GM's Tonawanda, N.Y., assembly plant.
Cummins is readying a new smaller diesel for the Dodge Ram pickup, as is Ford for the F-150 and other pickups. Will all of this diesel development trickle down into American diesel passenger cars, or will diesel remain predominantly a truck engine in the minds of the American driver?--Colin Mathews