Rudolph Diesel's compression-ignition combustion system has been around much longer than the vehicles it motivates today, yet it hasn't changed much in its basic operation. Each piston comes up in turn and supercompresses a charge of air and fuel until it combusts. Yet the latest state-of-the art technologies, such as high-pressure common-rail direct fuel injection, advanced materials, highly precise engine controls, turbocharging, and supercleansing exhaust after-treatment systems, have made modern diesels cleaner and more powerful, fuel-efficient, and refined than ever. And because all three U.S. heavy-duty pickup-truck makers offer new clean diesels for 2010-2011, now is a good time to take a closer look at each.
RAM 6.7-LITER CUMMINS I-6
Some say the Cummins diesel reputation alone is reason enough to want its latest industrial-strength turbodiesel six. Others might opt for it because it's the only one available with a choice of six-speed manual or six-speed automatic transmission. And many appreciate that it's the only one that meets ultra-tough 20101/2 emissions standards without diesel emissions fluid (DEF).
On the other hand, the latest Cummins inline-six diesel, available in 2011 Ram 2500 HD and 3500 HD pickups, trails the new GM and Ford diesel V-8s in peak power and torque by substantial margins-350 horsepower versus 397 and 400, respectively, and 650 pound-feet versus 765 and 800. Still, the diesel Ram 3500 ?? dualie with automatic transmission and 4.10:1 rear axle offers a plenty hefty maximum Tow Package GCWR of 25,400 pounds, maximum towing capability of 17,600 pounds, and a max payload of 5150 pounds.
Chrysler Engine and Electric Propulsion Engineering Vice President Bob Lee contends that the Cummins' output deficiencies will go unnoticed by most. "You'll find the performance of our trucks is quite comparable," he says. "It is advantageous to have bigger numbers for advertising, but if you look at what these trucks can do, we're all in the same neighborhood. If there are differences, it's a small portion of the market that may actually find them. And we can deal with torque pretty easily with gear ratios."
Cummins' turbocharger uses a sliding variable-nozzle device with integrated electronics that control it. Lee explains, "We use that variable nozzle as an effective integrated exhaust brake." Its side-mount location is also unique compared with the usual valley of a V-8, where, he continues, "things are hot and congested." Other advantages include its 350,000-mile overhaul interval and its 5-year/100,000-mile warranty, both direct results of the Cummins' long history as an anvil-tough industrial engine.