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Trail Test: 2012 Jeep Wrangler JK

Front View
Douglas McColloch | Writer
Posted December 1, 2011

Now 33 Percent More Powerful Than The Leading JK

When the latest Jeep Wrangler debuted in 2006, enthusiasts were quick to embrace it. Wider and more stable than the previous generation, with a suspension design that was as comfortable on pavement as it was capable on the trail, the Wrangler JK was clearly the most streetable bobtail in the history of the Jeep product line, and its nonpareil off-road chops hadn’t been compromised in the slightest.

There was only one key thing missing: namely, power. The kind of usable power that off-road enthusiasts demand when crawling over rocky sluices and stump-riddled logging roads. The kind of low-end torque that was offered in abundance by the previous-generation inline engine, but which was lacking in the JK’s 3.8L V-6. To make matters worse, the 3.8L was mated to a crude-shifting 20-year-old truck transmission that sucked whatever useful power that could be wrung from the engine at lower revs, and the result was a powertrain that felt weak and anemic at trail speeds, that delivered lousy mileage, and left enthusiasts pining for the return of the inline.

That’s all a distant memory now. For 2012, the 3.8L minivan motor has been replaced by the 3.6L Pentastar V-6 engine, which premiered last year as the base V-6 for the Chrysler vehicle line-up. Assembled at Chrysler’s Trenton, Michigan, plant, the aluminum-block DOHC engine is rated at 285 horsepower at 6,400 rpm and 260 lb-ft of torque at 4,800. That’s 75 more horsepower and a 33-percent power boost over the 3.8L’s 210 horsepower, and while the Pentastar’s peak torque output might not sound too impressive, 96 percent of it is available at 2,000 rpm, and much like the old 4.0L, the engine’s torque curve remains relatively flat from two grand up to redline. What’s more, its all-aluminum block is 33 pounds lighter than the engine it replaces, it meets PZEV emissions requirements, and it affords better mileage per gallon to boot — 21 on the highway and 17 around town.

A great engine, however, is only as good at getting power to the wheels as the efficiency of the gearbox that’s backing it, and in that regard, the old OHV 3.8L was hindered by the 42RE four-speed automatic, which wasn’t so great even when new in ’92. Enter the factory-option Daimler-sourced W5A580 electronic five-speed that’s also found in the latest-generation Grand Cherokee. Obviously enough, the A580 is much more technologically refined than its predecessor, with narrower ratio splits translating into greatly reduced torque-converter slip under throttle, smoother acceleration and quicker passing, reduced levels of interior noise, and better fuel mileage to boot. It was also designed to handle the torque and horsepower loads of the 5.7L Hemi V-8, so it should have no problem handling the Pentastar. You also don’t sacrifice much gearing with the automatic; a Rubicon Wrangler equipped with the juice transmission still sports a commendable 59:1 crawl gear.

For those of you who still prefer an old-school “real-man” grindbox - and according to Chrysler take rates, that’s about 20 percent of new JK buyers - the NSG370 six-speed returns as the standard stick. Transfer cases and axle components are mostly carried over as well. Wrangler Sport and Sahara models get the NVG 241 “Command-Trac” part-time two-speed with a 2.72:1 low-range, while the Dana 30 front and 44 rear axles are fitted from the factory with new-for-2012 3.21:1 gears (Why? Better mileage for Wranglers that mostly see pavement and which seldom tow; 3.73:1s are still an option). Rubicon Wranglers come equipped, as before, with the 4:1 Rock-Trac ’case with Dana 44s, electronic lockers a both ends, and standard 4.10:1 cogs.

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