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How do you stop a speeding Class 5 truck?

With some difficulty – unless, Chrysler Group suggests, it is an ’08 Dodge Ram 5500 Chassis Cab that features binder-saving exhaust-brake technology, which is new to the auto maker’s volume brand.

The Chicago auto show introductions of the 5500 and Dodge Ram 4500 Chassis Cabs this week continue the proliferation of the new 6.7L Cummins I-6 diesel that debuted last year on the Dodge Ram 3500 Chassis Cab.

The new 305-hp engine is standard equipment on the new trucks and features a variable geometry turbocharger that, aided by cooled exhaust gas re-circulation and high-pressure common-rail fuel injection, enables exhaust braking.

“Basically, it closes the vanes of the turbo so that it creates backpressure into the engine,” says Kevin Mets, senior manager-vehicle development and program management for Dodge’s medium-duty cab chassis program.

“And that backpressure provides engine braking.”

The common-rail fuel system, which features Robert Bosch GmbH injectors, also promises that the engine’s peak torque of 610 lb.-ft. (827 Nm) is more readily available.

“With higher-pressure common rail, you’re less dependent on engine rpm, so you can get a larger rpm band,” Mets says.

Compared with the engine’s 5.9L predecessor, Chrysler engineers bumped pressure 2,901 psi (200 bar) to 26,107 psi (1,800 bar). Peak torque now is available between 1,600 rpm and 2,600 rpm.

“We grew by 200 rpm at each end,” Mets adds.

The addition of the 5500 and 4500 to Dodge’s chassis cab lineup is the latest move in the brand’s strategy to expand its truck business.

“The commercial-vehicle market is essentially white space for the Dodge brand,” George Murphy, Chrysler senior vice-president-global brand marketing, says.

“We think we have already very, very loyal Dodge truck buyers looking to expand their fleet and had no place to go other than a competitor,” Frank Klegon, executive vice president-product development, says on the floor of the Chicago show. “So I think we’re going to bring some of those players into our fold.”

The new trucks will compete in the Class 4 and 5 segments, defined by gross vehicle weight rating of 14,000 lbs.-19,500 lbs. (6,350 kg-8,845 kg). Chrysler expects the segments will see a combined sales hike of more than 11% by 2012, growing to 18% by 2015.

Industry Class 4 sales approached 50,300 units – a 3.7% boost over 2005, according to Ward’s data. Class 5 sales totaled nearly 49,500, up 6.9%.

Related document: <i>Ward&#8217;s</i> U.S. Truck Sales by Weight Class

The new trucks build on the modification-friendly design that debuted on the 3500 Chassis Cab.

Key features include frame rails positioned 34 ins. (86 cm) apart, an industry standard for upfitters. And all chassis components are positioned below the rails, which are flat.

In addition, fuel and brake lines are routed together on the frame’s left side, while the fuel filler is routed through the frame – all of which reduce the need for structural modifications.

The new trucks also are equipped with a 6-speed manual transmission that affords Power Take Off (PTO) capability.

“What you can do with these vehicles is only limited by your imagination,” Mets says.

There are four available axle lengths from 60 ins. (152 cm) to 120 ins. (305 cm) and three different interior trim levels.

But Chrysler believes the new 6.7L Cummins diesel, which evolved from the previously available 5.9L model, represents a primary selling feature.

“From the research we’ve done, Cummins is the most recognized brand name when it comes to pickup truck diesels,” Joe Veltri, director of body-on-frame product marketing, tells Ward’s.

“(Cummins engines are) used all the way up through Class 8 trucks, so the name is very recognizable in the industry, whether it be pickup or chassis cab or over-the-road tractor-trailers. So the name has cachet, but also the reputation has been backed up by years and years of quality performance.”

Last month, Chrysler launched a 350-hp high-output version of the new Cummins I-6 in the Dodge Ram 2500/3500 heavy-duty pickup line, and early returns show an 85% take rate. The Texas market boasts the highest take rate with 91%, followed by California and Idaho. The new engine meets 2010 emissions standards.

Chrysler also is preparing a diesel engine application for its light-duty pickup line, as first reported by Ward’s last year.

Meanwhile, the auto maker advises detractors to take note of another feature on its Dodge 4500 and 5500 Chassis Cabs. If the engine’s exhaust braking capability does not suggest enough stopping power, Chrysler reminds the trucks also feature the segment’s largest rotors (15 ins. [39 cm]) and caliper pistons (2.6 ins. [6.6 cm]).

The ’08 Dodge Ram 4500 and 5500 Chassis Cabs will be built at Chrysler’s Saltillo Assembly Plant in Coahuila, Mexico.

The site also is home to the Dodge Ram 3500 Chassis Cab, Dodge Ram Mega Cab, Dodge Ram Power Wagon and Dodge Ram Heavy Duty 2500 and 3500 models.

– with Scott Anderson in Chicago

emayne@wardsauto.com