Road Test: Kenne Bell Grand Cherroke Unlimited
A Hard-Handling, Supercharged SUV
Many who switch from performance-minded cars to sport/utility vehicles are soon frustrated by the slow pace of life on the SUV bandwagon. Even the $38,000 Jeep Grand Cherokee Limited, which is the star sprinter on the otherwise lead-shoed sport/ute track team (thanks to DaimlerChrysler's wonderful new 235-horsepower 4.7-liter SOHC V-8) can't match the likes of the similarly priced BMW 328i. Even more humiliating: The Jeep's class-leaving 7.2-second 0-60 mph is no quicker than a Honda Civic Si. After losing a stoplight Grand Prix a time or two, some new SUV owners look to tuners like Kenne Bell Performance for more muscle.
With a Kenne Bell supercharger forcing air down its throat, the renamed Grand Cherokee Unlimited is boosted to an impressive peak of 325 horsepower. Now, it can confidently go trolling for Lexus GS 400s. Thanks to its full-time four-wheel drive, if the road is even slightly slippery the Unlimited will more than likely put a whuppin' on Mustang GTs and Camaro Z28s. We wouldn't be surprised if the Unlimited can come close to its 5.6-second 0-60 mph dry test track performance even in the rain. In Seattle, an Unlimited would more often than not beat a Viper GTS in a stoplight-to-stoplight sprint. Wait until the track dries to attempt to match the Unlimited's 14.2-second, 97.4-mph quarter-mile.
The heart of the Unlimited is a "twin-screw," Lysholm-type 2.2-liter Kenne Bell model 2200 supercharger running at 7 psi. Compared to both centrifugal blowers and turbos, a Lysholm-type produces full boost at very low rpm, helping the Unlimited's 4.7 single cammer reach a new peak of 362 pound-feet at just 3400 rpm. Benefits over the Roots-type blower found on the Ford Lightning: It requires less power to drive and boasts significantly lower charge temperatures, eliminating the need for a space-robbing intercooler.
However, without changes to the Jeep's computer systems, such gains wouldn't be possible. Kenne Bell adds an auxiliary microprocessor, which reprograms the fuel and spark strategy and monitors a new detonation/preignition detector. A mass airflow system replaces the speed/density system and helps the engine make peak power in extremes of weather and altitude. Other engine changes include tubular exhaust headers, high-flow mufflers, and a ram-air induction system.
Look for the Unlimited to slice another couple tenths off its 0-60 time if Kenne Bell is successful in another of its computer-tweaking efforts. To smooth shifts, the stock transmission computer shuts off fuel supply and retards ignition just before upshifts. This is the digital equivalent of a very slow upshift and feels especially punitive under boost. However, the proper code changes have so far been elusive.
Super-wide Goodyear Eagle F1s, size 295/45ZR18, on 8.0-inch-wide Prime 122 wheels helped raise maximum lateral grip on the skidpad from the stocker's lowly 0.75g to a whopping 0.87g for the Unlimited. New stiffer springs drop ride height almost 2 inches up front and a full 3 inches in back. There are also stiffer anti-roll bars and Bilstein shocks. However, the suspension mods need additional tuning: Despite the sticky Goodyears, slalom speed was only 1 mph quicker, at 62.5 mph, than the stock Limited. The Unlimited suffered from both off-throttle oversteer and power-on understeer, like a lot of high-powered all-wheel-drive sports cars. In extreme corners the Unlimited rolled on its springs to one position, paused a beat, and then rolled a bit farther. My guess is that the rear shock valving wasn't in tune with the front. At 136 feet, its 60-0 mph stopping distance was a mysterious 6 feet longer than the unmodified vehicle.
The Unlimited got few exterior changes beyond the sterling silver BASF paint job, which we bathed in dust during our photo shoot. If you're tired of the sedate pace in the SUV lane, take your Grand Cherokee-and about $15,000-to Kenne Bell and it'll be Limited no more.
|Kenne Bell Grand Cherokee Unlimited|
|Vehicle configuration||Front engine, full-time four-wheel-drive, four-door, five-pass., SUV|
|Engine type||90° V-8, SOHC, 2 valves/cyl.|
|Engine modifications||Kenne Bell model 2200 Supercharger, Kenne Bell Optimizer computer, Kenne Bell exhaust system, springs and shocks.|
|Horsepower, hp @ rpm, SAE net||325 @ 5000|
|Torque, lb-ft @ rpm, SAE net||362 @ 3400|
|Transmission type||4-speed automatic|
|Tires/wheels||Prime 122, 18x8.0, Goodyear Eagle F1 295/45ZR18|
|Other modifications||Leather seat surfaces, VDO Philips Carin global positioning system, Philips audio|
|Standing quarter mile, sec/mph||14.2 @ 97.4|
|Braking, 60-0 mph, ft||136|
|Lateral acceleration, g||0.87g|
|Speed through 600-ft slalom, mph||62.5|
|Base price (stock)||$38,000|
|Price as tested||$53,000|