CHELSEA, Mich. -- Big granite boulders two feet thick stack up as only one of many stair-stepping barriers to our four-wheeling progress on a definitive off-road track for Jeep at Chrysler's vehicle test facility in Chelsea, Mich.
Confronted by the lumpy tangle of rocks, a driver might prudently assume that the best way to reach beyond this blockade would be to find a path around it, but for this experiment we must climb over the cataract because the objective of this excursion is to test the off-road prowess of a vehicle stocking four-wheel-drive (4WD) equipment. Not just any set of wheels will do: For a tricky challenge like these granite steps, we're steering a five-door Grand Cherokee SUV, the most powerful and surefooted vehicle in the motor pool of Jeep.
Sturdy Grand Cherokee represents the original sport-utility vehicle and traces for decades in Jeep history with innovations like the Quadra-Trac automatic full-time four-wheel-drive (4WD) system with limited slip differential, introduced in 1973, and a watershed design in 1984 for the first unibody four-door SUV wagon.
The nameplate of Grand Cherokee emerged in 1992 on a new wagon which demonstrated that a SUV could conquer rugged challenges of the off-road world and still transport riders in comfort due to cushy cabin appointments. A larger version appeared in 1999 with a sleek shell and a luxury-lined cabin plus mechanical systems aboard which raised the bar for SUV performance, while a new scheme for Grand Cherokee of 2005 established even higher SUV benchmarks.
Now the 2009 Grand Cherokee issues constitute the most diverse array of models ever due to five powertrain choices. Engines include a thrifty gasoline-sipping V6 or a clean-burning turbo-diesel from Germany, a flex-fuel V8 that drinks gas or E85 ethanol plus the new HEMI V8 with MDS (multi-displacement system) to conserve fuel by clipping cylinders when boosted power is not needed, even a massive 6.1-liter HEMI V8 for Grand Cherokee SRT8 -- swiftest and strongest vehicle ever to wear the chrome-coated J-E-E-P badge.
Each of these engines can team with 4WD equipment to forge a unique traction-clawing SUV. Grand Cherokee stands tall in the traditional two-box format of a wagon but with all corners contoured and the horizontal lines chiseled and planed in streamline fashion. Wheel openings are shaped in a trapezoidal design with wheels pinned at corners of the platform and front and rear overhangs crimped to make transitions easy on steep slopes. In back, the liftgate window tips forward while the lower metal section falls vertically for a squared rump.
On the prow the hood extends forward to accommodate some big engines. A unibody structural design creates a rigid container that resists flexing and twisting when set in motion on pavement or dirt and ultimately enhances the smooth-riding manners of Grand Cherokee. Precise rack and pinion steering brings quick-response turns and produces a tight 37-foot turning diameter for maneuvering.
And the independent suspension system, with short/long arms up front and a live axle in back with five-link suspension geometry, enables front wheels to stretch high vertically for climbing over trail obstacles like boulders or thick tree trunks. And for rolling over such barriers, the chassis clearance measures to 9.5 inches.
Grand Cherokee puts luxurious appointments in the five-seat cabin and sophisticated electronic controls on three full-time 4WD systems through four models tagged as Laredo, Limited, Overland and SRT8. On Laredo with a 3.7-liter V6 engine, the Quadra-Trac I system has a single-speed transfer case for full-time 4WD management and no levers to pull.
With Limited and the 3.0-liter V6 CRD (common rail turbo-diesel) or flex-fuel 4.7-liter V8, the Quadra-Trac II system contains a two-speed electronic transfer case for full-time active 4WD operation and locked 4WD low range. With the 5.7-liter Hemi V8 for Limited and Overland, Jeep adds the automatic Quadra-Drive II system with front and rear electronic limited slip differentials (ELSD) for infinite torque management at each of the four wheels plus an electronic stability program (ESP) for checking lateral slippage and a dynamic handling system (DHS) to decouple suspension stabilizer bars when not needed.
And for souped-up Grand Cherokee SRT8, the electronic on-demand 4WD system is unique to save weight. The smart device normally has a 90 percent bias at the rear wheels to emulate a rear-wheel-drive (RWD) model, yet the torque split between front and rear wheels can change as needed for different traction venues. Entry point to the lineup of models for Grand Cherokee is a RWD Laredo stocking the 3.7-liter single-cam V6. It develops 210 hp at 5200 rpm with 235 lb-ft of torque at 4000 rpm.
Fuel economy numbers for the gasoline V6 tally to 16 mpg city and 20 mpg highway. A five-speed electronic automatic transmission applies to each of the five engines available for Grand Cherokee. For three Grand Cherokee trims -- Laredo, Limited and Overland -- the dual-cam 3.0-liter V6 CRD plant burns clean diesel fuel and employs a common-rail direct injection fuel system with electronically controlled turbo-charging to enhance engine power and torque.
It makes 215 hp at 3800 rpm but huge torque of 376 lb-ft between 1600-2800 rpm. And fuel consumption numbers run as high as 23 mpg for highway cruising, or 18 mpg in stop-and-go city traffic. For Laredo or Limited the flex-fuel V8 option amounts to a single-cam 4.7-liter V8 which increases in power and torque muscle for 2009. Jeep lists a 30 percent power boost to 305 hp at 5650 rpm with a 10 percent increase in torque to 334 lb-ft at 3950 rpm.
The Limited and Overland editions carry the new 5.7-liter HEMI V8 with VVT (variable valve timing) and MDS to conserve on fuel. It hits 357 hp at 5200 rpm with 389 lb-ft of torque at 4350 rpm. But that 6.1-liter HEMI V8 in the SRT8 soars to 425 hp at 6000 rpm with tall torque to 420 lb-ft at 4800 rpm.
All that muscle moves through a heavy-duty automatic transmission with electronic controls from the AutoStick, which has automatic or shift-it-yourself manual modes. Enormous 20-inch Goodyear Eagles peel rubber on pavement as the go-pedal goes down and the world's fastest Jeep zips from zero to 60 in less than five seconds. The base price chart for 2009 Grand Cherokee models stretches across a broad band from $30,000 to $45,000.