September 03, 2015
Tony Swan

To hear Chrysler tell it, the automaker’s 3.6-liter Pentastar V-6 essentially will be a new engine when it makes its debut in the 2016 Jeep Grand Cherokee, its first application in the FCA lineup.

Basic dimensional elements—bore, stroke, bore-center spacing—carry over, but the engineering team claims greater efficiency, improved torque characteristics, a small horsepower uptick, and better NVH performance.

New components include cylinder heads with an 11.3:1 compression ratio (up from 10.2:1), eight-hole ignition coils, platinum-tipped spark plugs, new valve springs, low-tension piston rings, lightened crankshaft and crank pins, extensive friction reduction, and cooling of exhaust-gas recirculation.

owever, the biggest single efficiency improvement, according to FCA engineers, is a revision to the engine’s variable valve timing, giving intake-side valves a two-stage lift strategy—low lift for routine power demands, high lift when the driver calls for more urgency.

Operating range of the variable-valve-timing system has been increased from 50 to 70 degrees to mitigate detonation during hot starts, improving operation of the automatic engine stop-start (ESS) function. Carried forward from the current V-6, the ESS system has been enhanced with a new high-speed starter motor in order to reduce cranking time and deliver quicker, smoother starts.

Conspicuous by its absence from the engine’s catalog of revisions is direct fuel injection. FCA chose to continue with an upgraded port-injection system, citing added cost and weight as tradeoffs that go with direct injection. (According to FCA, the new engine will weigh 326 pounds in the Grand Cherokee, four pounds less than the current V-6.) The engineers also looked at, and ultimately passed on, Fiat’s MultiAir induction system, for reasons of cost and U.S. market suitability. While it would be nice to see DI (or even MultiAir), this strategy gives FCA something in its pocket for future development of the engine.

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