Chrysler Pentastar V-6 Rare Blend of Versatility, Refinement

The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 18 years. In this installment of the 2012 Behind the 10 Best Engines series, WardsAuto looks at development of Chrysler’s Pentastar V-6.

Star athletes receive awards for performance on the field and some garner kudos for off-the-field accomplishments, including community service and (while in college) academics. A rare few are recognized for outstanding achievements in both.

By achieving in the automotive engine arena a rare blend of refinement and versatility, Chrysler’s 3.6L Pentastar V-6 wins a Ward’s 10 Best Engines award for a second straight year.

On the versatility side, by 2013 the engine will have replaced seven older V-6s to power 13 Chrysler Group vehicles. And, it likely will account for more than a third of the auto maker’s powertrains and contribute to about a 25% improvement in Chrysler’s overall corporate average fuel economy.

The Pentastar’s genesis dates back to the DaimlerChrysler days, in 2004, when a team was formed to do some initial design layouts, says Pentastar V-6 chief engineer Steve Gorgas.

“Daimler also was looking to do a new V-6, so there was collaboration between the two teams for about a year and a half. Then it broke apart. They went off and did their design, and we did ours.”

Daimler wanted a 90-degree engine to mount north-south in rear-wheel-drive vehicles. Chrysler needed a more compact 60-degree V-6 that would work in both north-south and east-west (transverse) configurations in rear-, front-, and all-wheel-drive vehicles. The engine needed to be that versatile.

Then the program had to survive the 2008 economic crash and Chrysler’s 2009 bankruptcy. “That was a very hectic time,” Gorgas says. “We went from DaimlerChrysler to Cerberus, then into bankruptcy. Then we came out and were linked up with Fiat.”

Yet, the engine program never was in jeopardy for either financial or internal political reasons. “It always was on the table to do because we knew how important it was to the survival of Chrysler,” Gorgas says.

As with any new-engine program, there were multiple priorities beyond versatility and the always-critical balance between output and efficiency. One was world-class refinement and noise, vibration and harshness characteristics.

“To be the new industry benchmark for NVH was very high on our list,” Gorgas confirms. So the team gathered NVH data (from engine-consulting company FEV), looked at all V-6s in the marketplace, narrowed them down to the top three and set out to beat them all.

Another goal was being “green.” That includes lead-free bearings, a centrifugal oil separator that reduces oil consumption and an “environmental” oil filter with a paper cartridge. “You can squeeze the oil out and incinerate it, vs. the spin-on filters on most vehicles,” Gorgas says.

Other key technologies include dual variable-valve timing; piston-cooling jets and a variable-displacement oil pump that reduces parasitic losses. The pump runs in low mode below 3,000 rpm, and then shifts to high mode at higher engine speed, to more closely match oil pressure to engine demand.

The Pentastar also features a completely integrated exhaust manifold. In this innovative design, all of the exhaust manifold geometry is contained within the aluminum cylinder head and the close-coupled catalyst bolts on directly.

To keep parts proliferation to a minimum, there are only small external differences among the V-6’s many disparate applications. The intake manifold is on a different side for north-south vs. transverse applications, and there are two front accessory-drive layouts (one with the alternator on the right, the other with it on the left).

For the ’12 Jeep Wrangler, some of the front pulley systems were changed and the alternator relocated. In the Pentastar’s coming role as the new standard engine in the much-upgraded ’13 Ram 1500 pickups, there’s little more than a different intake manifold and front cover and a small change to the oil pan, Gorgas says.

One fast-growing technology the Pentastar team is not sold on yet is direct fuel injection. “The payback for DI just isn't there,” he says. “It's a very small marginal benefit, and we were able to achieve all of our targets and goals without it. That reduces complexity on the machine line and the engine assembly line and gives us a cost advantage.”

Gorgas adds that Chrysler engineers have been studying DI for many years but so far have not seen it as much better than conventional port injection, at least on a non-turbo engine.

“DI is an enabler for turbocharging, but for a naturally aspirated engine, the benefit is rather small, so we are very competitive without it. And there’s a glide slope on price,” Gorgas says. “The price of port injection 15 years ago was very high. Now it's an off-the-shelf commodity. DI will certainly run that way.”

It’s hard to argue with that competitiveness claim. With the lowest induction restriction and exhaust back pressure, the Pentastar V-6 pumps out a hefty 305 hp and 268 lb.-ft. (364 Nm) of torque in the Dodge Challenger and ’13 Ram 1500 pickups.

The engine generates 290 hp and 260 lb.-ft. (353 Nm) in the Jeep Grand Cherokee, 285 hp and 260 lb.-ft. in the Wrangler and 292 hp and 260 lb.-ft. in the 300 sedan. In transverse FWD applications, exhaust restrictions are higher, partly because the front bank’s exhaust runs under the engine, so the output is slightly lower at 283 hp and 260 lb.-ft.

In all applications, peak power, torque and fuel economy are substantially improved compared with previous models powered by the seven old Chrysler V-6s. “From a performance perspective, we're talking 30%-40% improvement in power and 8%-10% in torque,” Gorgas says. “For fuel efficiency, it’s in the neighborhood of 15%-20% better.”

Despite all the advancements, there still is room for improvement down the road as customer demands and CAFE requirements ramp up, Gorgas says.

“We are continuously studying new technology enablers that can position the engine more competitively in both fuel economy and performance,” he says. “You could do some things to improve efficiency, but you might suffer in performance. So the challenge is to keep the performance, or even improve it enough to entice customers by giving them more than what they got last time but also significantly improve the fuel economy.”

There are three important areas for improving an engine’s efficiency: reducing pumping work (or throttling), reducing friction, and thermodynamic improvements, Gorgas says.

The former include such things as 2-step valve lift and Fiat’s MultiAir valve-actuation system, which already is being used on Chrysler’s 4-cyl. engines. The latter include higher compression ratios, cooled exhaust gas recirculation and direct injection.

“All of those things are being studied for future engines,” Gorgas says.