From the November 2017 issue
"We are still dealing with physics here. I just want you to remember that.” So says Erich Heuschele, manager of SRT vehicle dynamics, to the 20 or so writers he’s about to turn loose on a racetrack in the Jeep Grand Cherokee Trackhawk. We’re dealing with physics, sure, but also an earnest effort to defy them with equal parts horsepower and lunacy. Say “707-horsepower Jeep” to anyone who hasn’t been paying attention and they just wiggle a finger into an ear and squint at you. “Huh?”
That same phrase, the one with the big number lashed to that old army word, carries the mystical power to convince even the most jaded auto writers to back away from the lobster roll and don a balaclava. We did drive the maximum Jeep on public roads, but it says “track” right there in the name, so we also hit Club Motorsports, a New Hampshire club track so new that crews were still installing Armco barriers the week before we showed up. It’s a 2.5-mile StairMaster that works its way up and down 250 feet of elevation change at a maximum 14 percent grade. Keeping his new Trackhawks from bending that fresh Armco is something about which Heuschele cares deeply.
The topography, on the other hand—nobody’s too worried about that. Few things flatten the hills quite like this much horsepower. Insane as it may be, the 707-hp Hellcat engine should at least be familiar by now. Down 251 cubic centimeters compared with Mopar’s naturally aspirated SRT engine, it’s a 6.2-liter V-8 capped with a 2.4-liter IHI supercharger, which stuffs those eight cylinders with 11.6 psi of boost. In the Trackhawk, it makes its full complement of horsepower but loses five pound-feet of torque—to 645—due to a more restrictive exhaust system.
Caught up in a sledgehammer fight against the V-8, engineers applied the same blunt-force mentality to the rest of the powertrain: There’s a beefier transmission and a stouter transfer case, plus a reinforced rear driveshaft, half-shafts, CV joints, and differential. The front axle is the same as the regular SRT Jeep’s. That transmission is still a ZF eight-speed, now christened 8HP95 and officially rated to handle up to 811 pound-feet of torque. The transfer case routes torque forward with a wider chain than in the naturally aspirated SRT, with forged-steel sprockets instead of powdered-metal ones. Tube-wall thickness is up on the rear driveshaft, and the differential housing gains a mount, going from three to four. Inside, the diff itself goes from two spider gears to four, with a modified tooth geometry for greater strength. The Hellcat engine alone outweighs its naturally aspirated brother by 108 pounds, and everything aft of it adds another 105, according to Jeep. But that’s for identically equipped vehicles. At 5258 pounds, this Trackhawk actually weighs less than the last Grand Cherokee SRT we tested (at 5291 pounds), which was equipped with a panoramic sunroof.
Like the Challenger Demon, the Trackhawk gets the so-called Torque Reserve function to aid launching. With launch control engaged and the Jeep brake-torqued, this system cuts fuel to individual cylinders, allowing the engine to rev higher and the supercharger to build more boost—6.4 psi as it sits at the line. Lift your foot off the brake and the Trackhawk will squawk all four 295/45ZR-20 Pirellis on its way to a 3.5-second zero-to-60-mph time. We couldn’t match Jeep’s 11.6-second-at-116-mph claim for the quarter-mile; our best run took 12.0 seconds at 115 mph. But the Trackhawk’s acceleration made Club Motorsports’ 14 percent grade feel as flat as it looks in Google Maps’ 2D view—where, incidentally, the track still shows up as a dirt lot as of this writing. We told you it was new. Our one complaint about the engine is that we want more blower whine when we mat the accelerator. There’s a good bit under lighter loads, but at full throttle, it fades behind a raging gargle blaster of an exhaust roar so fierce it sounds as if the tailpipes are emptying into the cabin. The call is coming from inside the house!
Barging back down Club Motorsports’ hills demonstrates the rest of the Trackhawk’s skill set. It retains the SRT’s control-arm front and multilink rear suspension layout, but the springs are 9 percent stiffer up front and 15 percent stiffer out back. Not surprising for something so heavy and with so much rubber at each corner, it’s quite stable—a desirable trait on a course with lots of camber variances. But toe the brake and it’ll rotate. Lay into the brake and it’ll dance disconcertingly, even in a straight line. The steering is a touch slow but heavy enough for perceptible weight to bleed off as the nose starts to wash out. We half expected to find a fresh furrow plowed around our skidpad after the Trackhawk turned 0.89 g, and 2.6-ton vehicles don’t typically stop from 70 mph in just 168 feet without at least one major impact. That figure could be even shorter if the Trackhawk weren’t shy on clamping force. ABS never engaged no matter how hard we stomped the pedal. Describing his braking tests, assistant tech editor David Beard pantomimed sliding under his lap belt with both feet reaching toward the bottom of the footwell.
At 15.7 inches, the Trackhawk’s aluminum-hat front rotors grow 0.8 inch over those on the naturally aspirated SRT Grand Cherokee. The rears, at 13.8 inches, remain the same. Six-piston front and four-piston rear calipers are employed on both sport-utes, but the Trackhawk’s get a coat of yellow paint. Jeep hopes you like it, because it’s what you get regardless of exterior color or wheel choice.
Those yellow calipers are one of the Trackhawk’s few exterior tells. Others include the deleted fog lights, their nests hollowed out for an oil cooler where the right one used to live, and a cold-air intake at the former address of the left one. A new rear fascia accommodates the quad exhaust outlets. There’s a subtle “Trackhawk” badge on the lower-right corner of the liftgate and “supercharged” script below the Grand Cherokee lettering on the front doors. There are Trackhawk logos on the sillplates and the seats, a 200-mph speedometer—optimistic by only 20 ticks—and an available model-exclusive red-and-black interior.