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Introducing the 3.6L Pentastar V-6 and A580 Automatic
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
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
Wranglerengine 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 throughoverdrive.
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
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.
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