Behind the Pentastar
One of the most important products to come out of Chrysler is its next-generation V-6 engine, dubbed the Pentastar. The Pentastar is designed to be compact and lightweight and provides motivation for a variety of vehicles in Chrysler’s portfolio. Currently it is available in everything from the Chrysler 200 to the Jeep Grand Cherokee with plans for it to debut as the base engine in the Ram 1500 next year. The Pentastar was designed to be Chrysler’s engine of the future, meeting all foreseen U.S. and international emissions requirements without the need for an EGR system. The Pentastar is certified to Tier 2 BIN 5 and ULEV II federal standards, as well as PZEV in California.
We had an opportunity to learn more about the Pentastar V-6 and got a lot of insight after our tour of the Trenton Engine Plant during our last visit to Detroit. This nearly 1,000,000 square-foot factory facility was opened in summer 2009 and is packed with state-of-the-art technology and a manufacturing floor so clean you can see your reflection. It has an identical sister facility in Saltillo, Mexico, and at the time of our visit, Trenton employed over 500 people and was on pace to crank out 440,000 Pentastar V-6 engines a year, with plans to increase that total to 500,000.
At the foundation of the 60-degree Pentastar is a high-pressure die cast aluminum block with cast-iron bore liner and aluminum cylinder heads. Bore and stroke are 96mm x 83mm with cast aluminum pistons sporting low friction rings and forged steel connecting rods. The crank is made from nodular iron and features four-bolt main bearings. Two additional bolts are cross-fitted in the main bearing caps to provide a very rigid bottom end. A structural windage tray helps to reduce oil splash on the crank and help bottom end strength.
Cylinder heads are made from 319 T7 heat-treated aluminum and have dual overhead camshafts with roller finger followers and independent cam phasing is used on all four camshafts. Compression is 10.2:1 and piston cooling jets help cool the pistons to control temperature and detonation, allowing the V-6 to make its advertised power on 87-octane gasoline. Using a multi-port fuel injection system, the Pentastar breathes through a 74mm throttle bore.
In addition to the aluminum construction, other weight-saving tactics include the absence of exhaust manifolds. Instead of headers, the exhaust passages are cast directly in to the head, eliminating complexities in the exhaust stream and saving space. Equal-length downpipes, are tuned for torque as well. The Pentastar improves NVH and lowers weight even further by eschewing bracketry and having all of the accessories bolted to the engine itself.
The overall length of the Pentastar engine is only 19.8 inches long, more than 3.5 inches shorter than the 3.8L V-6 it is replacing in the Wrangler. Because it is so much more compact than the 3.8L, it allowed engineers to maximize intake airflow for more power. Wrangler has a unique intake manifold tuned for midrange torque and is the only Pentastar engine with the throttle body on the left side of the engine. Other Wrangler-specific changes include a unique oil pan arrangement to keep the engine oil within reach of the oil pump to prevent oil starving at extreme angles. To keep the alternator out of harm’s way, it is mounted high on the engine for maximum water fording ability. Wrangler also gets a 600-watt pulse-width-modulated fan for improved cooling performance and a full-face A/C condenser that is 20 percent larger.
To ensure quality, reliability, and durability, the Pentastar design went through 45,000 hours of computer analysis before the first engine block was cast. Once the engines were produced, they logged 12 million customer equivalent miles on the dyno and millions of actual field-testing miles. For easier service, oil change intervals are 8,000 miles and utilize a paper filter mounted in a canister on top of the engine.
The current 3.6L displacement is just the tip of the iceberg of the Pentastar’s potential. Its displacement can be scaled down to as little as 2.7L or up as high as 4.0L and it is also designed to work with a wide range of technologies such as direct injection, Fiat’s Multi-Air system, or turbocharging. Come to think of it, we wouldn’t mind a turbocharged 4.0L in our next Wrangler.