The Jeep Cherokee brand now has more than 40 years of history behind it and in many respects was responsible for transforming the SUV from a minor niche of the automotive market to a mainstream juggernaut. Following a decade during which the former DaimlerChrysler inexplicably re-branded the Cherokee as the Liberty in North America while keeping the original badge intact in the rest of the world, an all-new fifth-generation arrived last year with the old-school badge but some of the most radical changes yet to the skin and the platform.
Since its introduction in 2009, the Pentastar V6 lineup has been an enormous success for Fiat Chrysler Automobiles with more than 5 million units sold to date. The Pentastar in 3.6, 3.2 and 3.0-liter (the latter in China only) displacements is offered in everything produced by Chrysler larger than the 200. For the 2016 model year, Chrysler is rolling out the most substantial updates yet for this award-winning engine. At least one aspect of the revised engine points to the upcoming EPA Tier 3 emissions standards.
Most of the revisions to the V6 are pretty straightforward and increasingly common. Two-step variable valve-lift and variable cam-phasing with a range expanded from 50 to 70 degrees will help to reduce pumping losses and contribute to improved torque. Also aiding the torque output is a bump in compression ratio from 10.2 to 11.3:1.
The fuel injectors now have double the holes, going from four to eight for improved atomization of the fuel. However, Chrysler has opted not to follow the latest trend and continues to inject fuel into the ports upstream of the valves rather than directly into the combustion chamber. While this will certainly help keep costs down, during a preview of the engine, FCA powertrain engineering VP Bob Lee explained that they opted to stay with port injection for emissions reasons.
The primary benefit of direct injection is the charge cooling it provides when used in combination with the higher pressures from turbocharging. Conversely, spraying fuel directly into the combustion chamber complicates mixing air and fuel, especially when the engine is cold. This can often lead to higher emissions of particulate matter, aka the soot commonly associated with older diesel engines. Automakers have addressed the problem on diesels with particulate filters that capture the soot and then periodically burn it off at high temperatures.
Beginning in 2017, EPA Tier 3 standards will tighten the limits on particulate emissions for all light duty engines. If you take a look at the area around the tailpipe of many cars with direct injected engines, especially Fords with EcoBoost, you may notice black stains that are typically a sign of particulate emissions. In the coming years, we will like see many, if not all gasoline direct injected engines adopt particulate filters similar to those found on diesels.
Given the experience that many customers have had with mediocre real-world fuel economy on turbocharged GDI engines and rumblings of further adjustments to the way EPA label mileage values are calculated to reflect this, sticking to a normally aspirated engine could work to FCA’s long-run advantage.
Other changes to the Pentastar that will help its emissions performance is the addition of a cooled EGR system and a switch to 100 millijoule high-energy ignition coils. Efficiency will be aided by a two-stage variable displacement oil pump and smaller diameter crankshaft journals for reduced friction. The block casting has been reworked with new ribbing that helps improve noise, vibration and harshness while at the same time reducing the amount of material for lower weight. Despite the 13 pounds added for new hardware like the valve-lift adjusters and EGR, the net weight of the finished engine is only up by two pounds.
Auto stop-start is already included in several Pentastar applications like the Jeep Cherokee and Ram 1500 but it will be standard with all applications of the revised engine. Overall, the revisions to the second-generation Pentastar should boost fuel economy by about six percent. The second-generation Pentastar launches this fall in the Jeep Grand Cherokee and will roll out to other applications over the next year or so.