Targeting BMW, Volvo I-6 Turbo World-Class on All Fronts

The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 17 years. In this installment of the 2011 Behind the 10 Best Engines series, Ward’s looks at the development of Volvo’s 3.0L turbocharged I-6.

For as long as we can remember, Volvos have been known primarily for one thing: safety. A very good thing, certainly, but not a guaranteed deal closer for everyone.

T6 engine perfect match for Volvo S60.

Then, a few years back, Volvos started looking more stylish inside and out and handling better. They became more appealing to a wider variety of car buyers.

But who knew those clever Swedes could do grin-inducing BMW-like engines and wedge them sideways into great-looking cars with BMW-challenging driving dynamics?

Credit former owner Ford for much of the new Volvo S60’s overall goodness, but Volvo’s Gothenburg, Sweden-based engineers deserve the credit for the sweetness of this first-time Ward’s 10 Best Engines award-winning inline turbo six.

How sweet is it? Consider 300 eager horses at 5,000 rpm and 325 lb.-ft. (440 Nm) of tire-twisting torque between 2,100 and 4,200 rpm from 2,953cc. And that is without the cost and complexity of gasoline direct injection.

What’s more, there is no trace of turbo lag “even when dramatically slowing and then aggressively accelerating,” says 10 Best Engines judge Christie Schweinsberg. Other judges laud the engine’s delicious mid-range torque, expressive exhaust note and outstanding noise, vibration and harshness characteristics.

Based on Volvo’s all-aluminum I-6 architecture, this latest “T6” iteration boasts dual variable-valve timing, a twin-scroll turbocharger and substantial upgrades since the previous U.S. version introduced in the ’09 XC60 cross/utility vehicle.

The incremental upgrades include new friction-reducing materials, “super-ignition” spark plugs and a plate that scrapes oil off the rotating crankshaft to prevent high-rpm turbulence.

Transverse mounting makes Volvo T6 look different from most I-6 engines.

But perhaps the single most impressive thing about this world-class 3.0L turbo 6-cyl. is the fact it fits transversely between the shock towers of the midsize S60 to drive its front and rear wheels through a 6-speed automatic transmission. Among the few other passenger-car I-6s out there, how many are mounted transversely? Exactly none.

How did Volvo accomplish this? And why? “Our main criteria are safety and practicality. The best way to meet those expectations is with a transverse engine,” says Derek Crabb, Volvo’s vice president-powertrain development.

“But our (I-6-powered) competitors are all north-south installations. To deliver a transverse I-6 was an incredible challenge for our team.”

Not surprisingly, packaging was one of the toughest challenges. “Packaging determines the basic length of the engine,” he says. “Then you typically add the cam drive on the end. But we chose not to do that. We took out the length of the cam drive by taking a gear off the crankshaft up the side of the engine to the camshaft.”

Mechanically, that is fairly easy to do, Crabb says. “But with gears of this type at these (rotational) speeds, the biggest issue is NVH. We had a major NVH program to make sure that the frequencies those gears develop do not come through to customers’ ears.”

Engineers achieved this through intensive computer modeling and finite element analysis of the gear drives and how they interact with other engine and vehicle parts. Gear profiles and the numbers of teeth per gear were especially scrutinized, he says.

“To get the frequencies right, there are a lot of teeth on these gears. We had a full (computer) model of the gear drive all the way through the engine, engine mounts and vehicle structure to the customers' ears. The amount of detail we put into it was incredible.”

The engine also has no typical front auxiliary drive, says Karl Samuelsson, Volvo powertrain program manager.

“It's flat in the front; there’s nothing there,” he says. “The AC compressor and water pump are driven by this drive taken off the middle of the crank, and the generator is situated in a nonconventional manner. We had to go through a very different layout to compact it.”

There is no question the same-size BMW turbo I-6 was the Volvo team’s primary benchmarking target. “We have to be competitive in every way,” Samuelsson says. “But when it comes to straight sixes and refinement, once all the compacting technologies had been done, it was very much BMW, especially on the naturally aspirated version.

“In the turbocharging area, we've always been rather good at that, but we knew we had to compete with BMW on refinement, performance, fuel economy and everything else.”

Volvo engineers also benchmarked I-6s from Mercedes-Benz as well as V-6s from Audi and Honda for this second-generation 3.0L engine, Crabb says.

“We improved refinement and drivability. We increased the power and torque, as well, and did a massive improvement in fuel economy, more than 10% from the previous model year, on both the naturally aspirated and the turbo.

“We went through friction on everything that rotates, from the tappets to the gear drive, and improved the engine mounts and the gearbox,” he adds.

This latest version of the T6 engine positions Volvo as fully competitive not only in power and torque but also in fuel economy, refinement and drivability, Samuelsson says.

While its fuel economy of 18/26 mpg (13-9 L/100 km) city/highway hardly is class leading, it’s respectable considering the car is fairly heavy and that the T6 comes with standard AWD, he says. Ward’s editors logged a collective average of 22.4 mpg (10.5 L/100 km) in combined city and highway driving.

Volvo engines long have been members of a modular family, with much commonality among 4-, 5- and 6-cyl. versions. Samuelsson says while this latest iteration was a clean-sheet design, it followed that modular practice. The engine reached production in 3.2L naturally aspirated form in 2006, and the first 3.0L turbo version followed a year later.

This 2011 Ward’s 10 Best Engines award winner, available in ’11 XC60 and XC70 CUVs, V60 and V70 wagons and both S60 and S80 sedans, is the second-generation 3.0L turbo.

As good as this engine is, how can Volvo make it better down the road?

“Direct injection may be a step we will have to take,” Crabb says. “But also, particularly in Europe and Asia, downsizing is a technology that's becoming more and more necessary. And having an understanding of DI, turbocharging and transmission technology are keys to downsizing.”

While Volvo engines, in general, have been pleasers and performers in recent years, this 3.0L turbo I-6 stands out as the Swedish auto maker’s first Ward’s 10 Best Engines winner.

“We've done some quite nice engines in the past, but we are not high-profile in engines, so it was a very pleasant surprise when we suddenly were awarded,” Crabb says.

“This engine has been out there, but it comes out very well in the S60 because a lot of work was done on the dynamics of that car, as well. It’s a very good match to the vehicle. I think Cinderella has found her shoe.”