It was a showdown between the latest full-size performance pickups at the 2016 State Fair of Texas in Dallas, where SAE torque and towing ratings are worshiped as devoutly as homemade barbeque. At this year's State Fair, Ram's Rebel TRX 2017 concept was pitted against Ford's eagerly awaited production 2017 F-150 Raptor—two trucks aimed at the most rabid fans of each brand and off-road pickup enthusiasts in general.
Under the hoods
Heart of the Ram Rebel TRX concept is a 6.2-L supercharged Hemi V8 delivering an SAE-rated 575 hp (428 kW) mated with the 8-speed 8HP70 automatic. According to FCA North America, the TRX concept is the most powerful half-ton truck the company has ever built.
The 6000-lb GVW (2721 kg) concept "demands an engine with specific abilities in a small package. Reaching such horsepower per-liter efficiencies requires forced induction,” Bob Lee, FCA North America's propulsion system engineering chief, said. He explained that new engine and driveline calibrations were required, including in the Ram 4x4 Performance Control System, to optimize the expected duty cycle for punishing off-road driving.
The engine uses a twin-screw Lysholm-type supercharger of the type fitted to the 707-hp (527-kW) "Hellcat" version of the Hemi. The inherently tall stance of the blower/intake manifold system made for a tall engine package. This in turn required alterations to the Ram 1500 engine bay and forward cab area, and a modified Ram 2500-series HD hood is used for additional clearance. A custom induction system was designed to keep the ravenous blower adequately fed.
“This is the first time we’ve mated such an engine to this drivetrain and this vehicle architecture, so there was a lot of adaptation required,” Jeff Reece, vehicle development engineer from FCA North America’s SRT group and member of the Rebel concept build team, explained during the State Fair. A forged-steel crankshaft with induction-hardened bearing surfaces is able to withstand firing pressures of 1,595 psi (110 bar). A specially tuned crank damper has been tested to 13,000 rpm.
Ford engineers took a very different route to performance on the 2017 Raptor, using Ford’s all-new second-generation 3.5-L twin-turbo high-output V6. The EcoBoost engine is SAE-rated at 450 hp (335 kW) and 510 lb·ft (691 N·m), delivered across a wide power band.
“Raptor was designed to be a no-compromise, off-road performance machine,” said Matt Tranter, Ford Performance Engineering Supervisor. “That is why we made the switch from the cast-iron V8 to the aluminum block, high-output GTDI V6 EcoBoost engine that our team tuned to add 39 horsepower and 76 lb·ft of torque for today’s Raptor.”
Internal engineering upgrades include a new twin fuel injection set-up that employs both direct and port-injection strategies; stronger and lighter crank and valvetrain components; a redesigned twin-turbocharger system with electronic wastegate and a redesigned valve train and variable-displacement oil pump.
Among the high-output EcoBoost performance enhancements for Raptor, according to Ford, are more aggressive turbo compressors with increased boost calibrations, cast stainless steel exhaust manifolds (feeding full dual exhaust), oil-cooled pistons and more aggressive engine control calibrations.
“Looking at the torque curve of the Raptor’s EcoBoost engine, you see the twin turbos spool quicker for faster time to torque—it hammers quick and keeps delivering torque for a more brawny feel than its V8 predecessor,” said Al Cockerill, Raptor’s powertrain development engineer.
10-speed vs. 8-speed
The new Raptor represents a milestone for Ford and for the auto industry overall—the first production application of a 10-speed planetary automatic in a light-duty vehicle. Mated to an exclusive-to-Raptor transfer case and managed by a six-mode Terrain Management System, the new 10R80 was co-developed with General Motors Global Propulsion Systems engineers (see July 2016 cover feature, http://magazine.sae.org/auto/).
The new 10R80—8th, 9th and 10th gears are overdriven—brings new features including a standard Auto Start-Stop function and an integrated electric fluid pump. Its 7.4 ratio spread and Ford-patented hydraulic control system better optimize the power and torque curves of the new EcoBoost engine, according to Ford.
Raptor’s all-new adaptive shift algorithms monitor more than a dozen powertrain and driver inputs in real time. Drivers have normal, sport, weather, mud/sand, rock/crawl and Baja modes at their disposal for tackling nearly any traction condition. A high-speed, one-way clutch allows for non-sequential shifting.
While it makes do with "only" eight forward ratios, the Ram Rebel TRX concept's ZF-designed 8HP70 has more than enough input torque capacity to handle the supercharged V8. The truck is fitted with paddle controls for manual shifting capability and in Auto mode, more than 40 individual shift maps are available for very specific driving, performance and fuel-efficiency conditions, engineers said. Sending torque to the four driving wheels are a standard Ram 1500 front driveshaft and a custom rear drive shaft.
'Bones' of the trucks
FCA and Ford engineers took different paths for their performance trucks' structures, the Ram Rebel TRX concept relying on a high-strength-steel-intensive cab and cargo bed, while the Ford guys employ the same 5000- and 6000-series aluminum alloys from Alcoa and Novelis as those of the standard F-150. Both trucks use fully boxed steel ladder frames.
Under the skin of the Rebel, front and rear bypass-type performance shocks deliver fast-reaction time, improved damping and improved heat dissipation for traversing harsh terrain at speeds greater than 100 mph, engineers claim. The truck's "purpose-built hourglass design," as Ram brand boss Jim Morrison describes the exterior styling, includes six inches (152 mm) additional width versus the current production Ram Rebel. This enables the concept vehicle "to house the 37s [mammoth 37-in-diameter tires] at full jounce and rebound—you can get full-wheel motion here with the extra six inches and the big fenders that are built into the truck,” Morrison said.
Ford's latest Raptor sports new gas-charged 3.0-in-diameter (75 mm, up from 2.5-in) Fox shocks. They feature a base valve piston to allow lower internal gas pressure, for increased ride comfort on the road. The internal bypass in the front and rear shocks has nine distinct zones that progressively manage shock forces, allowing for smooth on-road trips along with hard-hitting off-road driving.
To be or not to be?
Industry speculation is rampant regarding whether or not the Ram Rebel TRX concept will make it to production to give the Ford Raptor competition in the off-road performance truck segment.
"One of the reasons we build a concept vehicle is to gauge interest, right, So we are looking for feedback. We made it a runner so we could learn from it," Reece told Automotive Engineering at the State Fair. While FCA's next steps are yet to be determined, the Rebel TRX and its rapid 77-day gestation are impressive.Continue reading »