Moses Ludel’s 4WD Mechanix Magazine – HD Video: 2012 Jeep Wrangler Powertrain Changes
Jeep® engine advancements have always drawn attention. When rumor slated the award-winning 3.6L Pentastar V-6 for 2012 Jeep JK Wrangler models, the anticipated 40% bump in horsepower was certainly welcome!
For serious off-roading, the real measure of a 4WD’s engine capability is low-end torque. Torque is the key to stump-pulling power. In the earliest Jeep military and civilian CJ models, this took form as long-stroke, small bore engines with low compression. Though the horsepower figures were paltry by modern standards, torque was respectable and available at very low rpm.
This trend continued through the 1966-71 Dauntless V-6s and AMC’s inline six-cylinder era. Under ’80s emission control constraints, the 258/4.2L Jeep inline six mustered its peak torque (210 lb-ft) by a low 1,800-2000 rpm. This provided a distinct advantage, rivaling the quick torque rise of diesel engines!
When the YJ and TJ Wrangler turned to the XJ Cherokee’s 4.0L inline six, many noticed the change in torque character. Despite the boost in horsepower over the 4.2L, from 112 to as much as 190 in the late TJ Wrangler’s 4.0L MPI design, the 4.0L six developed its peak torque at a higher 3,200-3,500 rpm.
Any heavy-duty truck or off-road equipment operator knows that 235 lb-ft torque at 3,200 rpm is a poor equation. Diesel engines and ‘stump pullers’ need bottom end power with a quick torque rise…4.0L buildups like the Mopar Performance stroker 4.7L inline six are living proof. Above, the 3.6L Pentastar outperforms the 3.8L V-6 in both horsepower and torque—while boasting a quick torque rise.
Undersquare designs (smaller bore diameter than stroke length) and closer to square engines make peak torque at a much more useful, lower rpm. For maximum fuel efficiency* and off-pavement four-wheeling, that’s the formula for successful stump pulling performance.
*The magazine’s 5.9L Cummins powered 4WD Dodge Ram 3500 weighs 7,800 pounds curb weight. On the trip to Portland for the 2012 Wrangler media launch, the truck averaged 25.2 mpg on highway and interstate, its best efficiency to date. This engine peaks torque at 1,600 rpm, and at 68 mph, the tachometer reads 1,950 rpm. The engine runs most efficiently between 1,600 and 1,950 rpm.
Since the inception of the JK Wrangler platform, the 3.8L V-6 has suffered from insufficient bottom end torque. The stock 3.8L V-6 peaks torque at just over 4,000 rpm. On a Rubicon Trail rock pile, such speed would be totally unwarranted. While a durable engine and highly praised in the popular Caravan models, this 3.8L engine failed to turn Wrangler owners’ heads. Its torque rise creeps to an overall figure of 237 lb-ft—at a lofty 4,000 rpm!
In addition to the impressive 83 horsepower gain with the new 3.6L Pentastar V-6, the bigger gain for four-wheeling is actually the quick torque rise. While the peak torque of 260 lb-ft is at a high 4,200 rpm, this engine rises from an idle to 250 lb-ft torque by 2,000 rpm. This kind of torque harkens back to the legendary 258/4.2L inline six! Add variable valve timing, 10.2:1 compression, DOHC 24-valve hemi cylinder heads, and the new Wrangler engine is a totally new paradigm for both on- and off-highway performance!
The 2012 JK Wrangler engine change is significant in itself. Jeep did not stop there, though. To enhance the feel and power flow of the new engine, the Wrangler gained the rugged A580 five-speed automatic. This high tech transmission, designed for the 5.7L Hemi V-8, boasts a lower first gear ratio and closer gear spacing from 1st through overdrive.
An A580 automatic transmission option provides constant throttle response. On-highway driving no longer involves hunting and pecking for the right gear—no more speed flareups or lugging! Instead, the 2012 Wrangler accelerates from a standing start to 60 mph responsively. This also applies when passing and during 40-60 mph tests.
Note: The A580’s low first gear ratio allows use of taller axle gearing for fuel economy. 3.21:1 axles are new for 2012…Desirable 4.10:1 remains available for off-road use Rubicon models. 3.73:1 is also available on several equipment packages. All 2012 Wranglers offer performance and economy gains.
Of course, there is alway a call for manual transmissions on Jeep 4WD utility models. The NSG 370 six-speed fills this need precisely. Again, there is a ratio for each occasion, regardless of load, acceleration demand or the need for braking.
2011 provided the necessary sheet metal changes to accommodate the 2012 engine change. This year brings together the complete package. The 3.6L V-6 and transmission offerings provide the most versatile, efficient and technologically advanced Wrangler powertrains to date.