Complementing the 6.7-L Cummins turbodiesel in Ram Trucks’ 2014 heavy-duty lineup is Chrysler's 6.4-L Hemi V8 that will be available from the 2500 models through the 5500 chassis cab. The engine delivers SAE-certified 410 hp (306 kW) at 5600 rpm and 429 lb·ft (582 N·m) at 4000 rpm—best-in-class output among gasoline-powered pickups, the company claims.
“There’s strong customer demand for increased capability without having to step into that diesel,” said Kevin Mets, Head of Engineering for Ram Heavy-Duty Pickup Trucks.
Mets' team also spent a great deal of development effort on the heavy-duty trucks' chassis systems—both front and rear suspension, in particular. A key goal was to improve ride and handling without sacrificing the durability and capability demanded of such work vehicles.
6.4-L Hemi developed for truck duty
Though it debuted in the 2011 Dodge Challenger SRT8 (and is used in other Chrysler, Dodge, and Jeep SRT8 models), the 6.4-L was originally designed as a truck engine, according to Mets. Its components were optimized to satisfy tough durability and market requirements.
“An active runner intake system [helps to] provide that low-end torque that is required in a heavy-duty truck, but without sacrificing that high-end power,” Mets said. “If you look at the torque curves between this engine and our competition as well as the 5.7-L Hemi, the 6.4-L generates as much torque as the others but at 800 to 1000 rpm less.”
Another truck-specific feature is an optional dual-alternator setup for chassis-cab applications. This marks the first time Chrysler has offered a gasoline application in the 4500 and 5500 chassis cabs, according to Mets.
“Designed as a truck engine, we were able to do things like packaging an optional dual alternator; so straight out of the factory, a dual alternator with 380-A [220 and 160 A] output…which is very significant for those electric applications [customers] put on the back of a chassis cab,” he said.
The 6.4-L Hemi shares the basic iron block/aluminum heads architecture of the 5.7-L Hemi, as well as its manufacturing process. It also borrows Chrysler’s fuel-saving cylinder-deactivation system, which shuts down four cylinders when in steady-state operation. This is Chrysler’s first application of cylinder deactivation to the heavy-duty pickup truck and chassis-cab markets, according to Gary Rogers, Chief Engineer for Engines.
While fuel-economy figures for the 6.4-L trucks are not yet available, engineers placed a great deal of emphasis during development on features to improve fuel economy, Rogers said.
“We’ve put a lot of hardware in the engine for that purpose, like the cylinder deactivation, the cooled EGR [exhaust gas recirculation], the active intake, variable valve timing, and the active thermostat—those are all fuel-economy features,” he said.
To better manage high temperatures and improve durability, engineers specified “premium" materials for the 6.4-L application, Mets shared. These include stainless steel exhaust manifolds, steel gaskets, and fasteners as well as sodium-filled exhaust valves and an upgraded valve-seat material.
“We also have a robust high-volume oil cooler and oil jets for cooling the pistons. These are all key things to keep this engine running at a good temperature for long engine durability and longevity,” he said.
The big Hemi is mated to the 66RFE six-speed automatic transmission. It will have the same five-year, 100,000-mi (161,000-km) warranty as the Cummins turbodiesel. “That’s how confident we are in this engine,” said Mets.
New link-coil rear suspension for 2500
In the chassis, the major change for 2014 is the new five-link-coil rear suspension system for the 2500, which benefits from lessons learned on the 1500’s link-coil system introduced in 2009. Importantly for the HD segment, there is “absolutely no compromise in payload,” Mets said. “As a matter of fact, we increased the GVW [gross vehicle weight] all the way up to the class max 10,000 lb in both our gasoline and our diesel applications.”
The system offers a 40-lb (18-kg) weight reduction compared to the previous leaf-spring configuration, Chrysler engineers claim. (See video at http://video.sae.org/11712/ for more details on the 2500’s rear link-coil system.)
An active load-leveling air suspension, for which an airbag replaces the coil spring, is also available on the 2014 Ram 2500. Load capacity is not sacrificed, and the load-leveling function detects load on the rear suspension and automatically increases air pressure until the vehicle reaches normal ride height.
“We wanted the vehicle to have a 1° positive grade angle—whether loaded or unloaded—for a very solid, strong look on the road,” Mets explained. “Unloaded, the air suspension is about two inches lower than the steel suspension, offering you better ingress and egress.”
The air suspension system has two modes—normal and tow—that can be controlled via a button on the center stack. In tow mode, the grade angle is lowered to 0° “so when you hook up to a trailer, you’re looking more level as opposed to pitched in the center,” Mets said.
Engineers took a different approach with the air suspension for the 2014 Ram 3500. “We actually kept the main leaf, but we softened it up, and we added the airbag [and] an upper control arm to manage the axle torsion,” said Mets.
The supplemental airbags allow for more unladen suspension movement. When a high-load capacity condition exists, the air suspension automatically fills the rear airbags to level the truck and improve stability and ride quality, including with a claimed best-in-class 30,000-lb trailer in tow.
As on the 2500, the 3500’s air suspension has two modes—normal and trailer—and is optional on both single and dual rear wheel models.
Three-link front suspension
In the front, the Ram heavy-duty line features a three-link front suspension to ensure roll stiffness—an important characteristic especially in trucks with heavy payloads. Roll stiffness is measured by the amount the truck’s body tips side-to-side, independently of the wheels, during cornering. The greater roll stiffness enables engineers to better optimize the trucks’ front-to-rear roll-stiffness ratio.
“We’re now putting the three-link front suspension on the 2500,” Mets explained. “It has 40-inch-long—these things are massive—front radius arms. They actually mount to the frame, back at the transmission cross member, [and] they go all the way forward to the front axle; they mount to the axle through some very huge cam-style bushings. This suspension system really is a key for us to be able to increase the GVW of this truck all the way to 10,000 lb,” he said.