PSU (formerly PUG) — the Pentastar V6 engine upgrade

V6 PSU engine

PUG - upgraded Pentastar engineThe Pentastar upgrade has finally arrived, though, for the moment, only for the Jeep Grand Cherokee. We had written, “We are expecting revised heads, direct injection, and better cam phasing, possibly affecting exhaust as well as intake, or altering the valve lift.” In most areas, we were right — but it doesn’t have direct injection, at least not yet. That might be awaiting cleaner gasoline.

The official name appears to be PSU, rather than the original PUG. It’s possible that PUG is being reserved for a future upgrade. Typically, engine families go through numerous updates over their lives.

Torque is over 15% higher at engine speeds below 3,000 rpm, for better drivability; at the same time, gas mileage increased by over 6%. On the Grand Cherokee, horsepower rose by 5 hp to 295 hp.

The revised engine uses two-speed variable valve lift; the low-lift setting cuts “pumping work” at low speeds, for a fuel economy gain of up to 2.7%, while the high-lift setting preserves power. A torque-driven cam phasing valve timing system cuts oil demand, and increases the system range from 50° to 70°, cutting knock during hot starts and increasing the ability to use the stop-start system. Valve timing was recalibrated to take advantage of the new intake manifold.

variable cam lift in V6

Pentastar V6 upgrade

The Pentastar upgrade engine (PUG) has cooled exhaust gas recirculation to cut knocks and reduce pumping losses. A new intake manifold with longer runners boosted torque, and various changes allowed an increase in compression ratio from 10.2:1 to 11.3:1. Heads include high-tumble intake ports and shrouded combustion chambers.

headless V6

New fuel injectors have eight holes for better atomization. 100-millijoule high-energy ignition coils provide sparking power to the platinum plugs.

As predicted, internal friction was reduced, by using HG-R1 on the timing drive guide-faces (the new Pentastar is the first production engine to use this material), low-tension piston rings, new valve springs, and piston pins with a hard carbon coating.

high valve lift

low lift cam

Redesigned components cut engine weight, despite 13 pounds of added content, with the lightest Pentastar coming in at 326 lb. The thickness of some die-cast components was cut, windage-tray weight was slashed by 19% and front-cover weight was cut by 5%. Two-piece oil pans were eliminated, except in Trail Rated vehicles. Main bearings and crankshaft pins were trimmed, cutting six pounds and reducing friction.

The revised engine has 4.7 million “customer-equivalent” test miles.


Possibilities still unknown for the PSU

A patent application from 2011 by Chrysler’s Richard H. Sands and Alan G. Falkowski can reduce the size of engines, helping the company to either fit larger engines into their cars, or to lower their hoods. The patent applies to in-line and V-engines alike, so it could be used for the upcoming Hurricane turbocharged four-cylinder; but the drawings are taken from a V6 engine.

patent for heads

The new setup would integrate valve controls into the head, rather than having them sit on the outside with a separate cover; passages inside the head would provide access to the valves. This would save space and reduce cost. Thanks, Steven St. Laurent.

Engine decoding guide • Main Pentastar V6 page at allparPentastar engines site

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