The default engine for Ram Chassis Cab is the 330-horsepower Hemi with a G56 manual or five-speed automatic. The option is the Cummins ISB 6.7--at $5555, it's essentially the same price as the current ISB 5.9-liter diesel option. The larger capacity is driven by emissions, primarily to maintain the low-rpm torque characteristics, since fueling and turbocharging feed mid- and upper-rev output. It shares bore centers with the 5.9 and is no bigger externally, though the larger stroke required crankshaft-balance reprofiling to fit in the block and clear the skirts, and the cylinders have lost the water jacket between them; the 6.7 keeps the piston oil coolers, and the compression ratio's still healthy at 17.3:1. The architecture is similar to the ISB 5.9, but carryover is 40 percent or less.
Things have changed more on the outside, with watercooled EGR over the exhaust manifold, a MAP sensor and throttle on the intake horn, and a 14-vane variable-geometry turbocharger mounted a bit lower and further back. Also new are a layered oil pan, viscous vibration damper, and modified pulleys (including an overrunning alternator pulley so it doesn't squeal like a pig at shutdown), all designed to minimize NVH. Combined with the third-generation common-rail fuel system that handles multiple injection events per stroke, the larger engine is quieter than the one it replaced, keeps maintenance intervals and design life of 350,000 miles to overhaul, and weighs only slightly more.
On the Chassis Cab, output is pegged at 305 horsepower at 3000 rpm and 610 pound-feet from 1600-2600. No clutch-engagement figure was quoted, but no one at Dodge disputed our assessment of nearly five inches of stroke giving "something more than 350-375 pound-feet." Don't fret if you were expecting more out of a larger engine. Since flat torque curves and operating economy are more important than horsepower to fleet operators and the G56 is limited in input capacity, torque took priority over a 20-horsepower drop from the pickup. This 6.7 is said to get better fuel economy than the 325/610 5.9. Look up any commercial engine, and you'll find top ratings reserved for fire apparatus and RVs, vehicles that seldom carry the engine's max load or only do so for limited intervals.
The electronic control of the VGT14 turbo can produce nozzle closure of 90 percent, doing the same thing as an exhaust brake. Therefore, for the first time, a factory exhaust brake is offered, and at $300 it's a lot cheaper than previous aftermarket units. The exhaust backpressure limit stays at 60 psi as does the maximum braking horsepower available (about 190), but from 2400 rpm down to 1000, the braking is better. The retarding effort of the VGT without the brake option is close to that offered on earlier models equipped with the "Ram Brake" exhaust brake.
On diesels with the six-speed automatic, the exhaust brake and powertrain controllers all cooperate, delivering automatic downshifts as the brake decreases speed to the next gear range. If on cruise control, the brake will operate to attempt to maintain the set speed on descents. The integration has brought an impressive setup, especially in light of the modest fee, and if you buy one secondhand that didn't come with the brake, we expect Mopar will offer a retrofit kit--it's mostly software and a switch below the climate control.
Aisin builds the commercial six-speed auto, a unit with a moderate first gear and two overdrives for relaxed highway miles. A glance at the 35-horsepower (max) PTO, big pan, and $2300 option tag, you can see this is real medium-duty stuff--and a stout 220-amp alternator is available as an option.
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