BMW Turbo I-6 Epitomizes ‘EfficientDynamics’ Engineering Vision

Special Coverage

Story Behind 10 Best Engines

The Ward’s 10 Best Engines competition celebrates 15 years of outstanding powertrain development. In this latest installment of the 2009 series, Ward’s looks at the design philosophy behind BMW’s turbocharged 3.0L I-6.

If you’ve seen recent BMW AG ads, you know the auto maker’s engineers march to a mantra of “EfficientDynamics.”

Yes, it’s one big word, like a Web address, and it signifies that efficiency-enhancing improvements will not be made at the expense of the performance character that long has been a part of BMW’s DNA.

Put another way, it is the pursuit of an athletic driving experience while simultaneously lowering consumption and emissions.

“We have a history of sporty performance,” BMW North America Engineering Vice President Tom Baloga explained a year ago when we wrote about this delightfully smooth and powerful 300-hp twin-turbo 6-cyl. engine, now a 3-time Ward’s 10 Best Engines award winner.

“Dynamic performance is the reason people are so enthusiastic about our products, so the highest priority in anything we do to make changes is to not allow it to compromise performance.”

After testing BMW’s 3.0L twin-turbo inline 6-cyl. in an ’09 135i coupe, the company’s smallest and lightest U.S.-market 4-seater, Ward’s editors described it as “all-around awesome.”

BMW ’09 135i coupe

Then they called it, “Arguably one of the best volume internal-combustion engines ever produced.”

No surprise, then, that the key priorities when this engine was designed nearly a decade ago included dynamic balance, efficiency, power and torque.

“Efficiency and power can be contradicting,” says BMW Drivetrain Development Product Manager Hans Hohenner. “But we had that challenge, and we faced it.”

Among many other things, BMW developed a “more-efficient burn situation in the combustion chamber” and found ways to reduce both engine weight and friction from the very beginning of the design.

The original naturally aspirated N52 version that debuted in Europe in 2004 arrived in North America soon after in a new 328i. A turbocharged variant always was part of the plan, Hohenner says, and that development began about the time the N52 was done.

Designated N54, the turbocharged version debuted two years later in Europe and in the U.S. in 2006 in the wonderfully quick ’07 335i.

The engine then migrated to the 3-Series convertible and sedan, 5-Series sedan and wagon, X6 “Sports Activity Coupe,” ’08 1-Series coupe and convertible and, most recently, the ’09 Z4 roadster.

Before long, it will be in the new-generation 7-Series and probably most everywhere else there’s a BMW engine bay needing fuel-efficient power. With such a wide variety of applications, this could be today’s Teutonic equivalent of the iconic Chevrolet small-block V-8.

Common-rail direct-gasoline injection with piezo-electric injectors centrally located in the aluminum cylinder head are among its key feature.

This system, using “spray-guided” direct injection to enrich the fuel mixture, reduces exhaust temperatures and increases combustion efficiency. It works in harmony with evaporative combustion chamber cooling to reduce fuel consumption while achieving truly impressive output of 100 hp and 100 lb.-ft. (136 Nm) of torque per liter.

In addition to DI matched with two compact turbochargers and air-to-air intercoolers, the N54 engine boasts lots of other advanced technologies, including an aluminum block, BMW’s Double Vanos (dual variable valve timing), an external engine oil cooler and a 400-watt electric water pump.

The twin turbos also are designed to spin in opposite directions with very low moment of inertia to essentially eliminate turbo lag.

Hohenner, who was part of the original design team, concedes one of the toughest challenges was meeting current and future U.S. and European emissions standards without sacrificing power or torque.

“You always have a lot of challenges because the targets have to be very challenging,” he says. “Yet, we have to have a chance of reaching them. To meet the output and fuel-efficiency targets as they were in the beginning, we were never assured of meeting the emissions standards. And these are moving targets.

“So we developed a strategy during development of the design that allowed us to meet those very strict emissions standards, including California ULEV (ultra low emissions vehicle). We had to change the strategy in heating, but we did achieve our targets.”

As fuel-economy requirements continue to ramp up on both sides of the Atlantic, is there still room for improvement? Yes, Hohenner says. “The problem is that it’s getting costlier. That is the challenge, to continue to improve but keep the cost on a track where (the engine) is still affordable.”

Combustion efficiency enhancements and friction reduction both will be targets, along with minimizing parasitic energy losses by electrifying more engine accessories.

Many improvements still can be made to near-perfect engine.

“We started early with electrifying our engines and drivetrains, and I think a lot more things can be electrified,” Hohenner says. “This engine has a motor-driven water pump; European versions have electric oil pumps, and future improvements will come from electrifying other engine-driven ancillaries to reduce parasitic drag on the engine.”

“Ancillaries that are traditionally mechanical can be electrified and integrated on an as-needed basis,” he says. “When you need it, it runs. When you don’t, it doesn’t. You don’t need to spend some power to drag it along. A mechanical pump always has to drag even when I don’t need it.”

Another important area for improvement is electronics packaging. “There is not a lot of room in the engine compartment to find a cozy place for the engine electronics,” Hohenner says.

Among other things, he would like to make the engine-control unit smaller and mount it closer to the engine, which would eliminate a fair amount of wiring. “Perhaps we could mount it directly to the engine with different cooling. We would no longer need a specific cooling fan for it, and we could use that space for other things,” Hohenner says.

Still another future enhancement likely will be addition of BMW’s Valvetronic valve lift control (already on the naturally aspirated N52), which eliminates the need for a conventional throttle mechanism.

Also on the agenda will be U.S. applications of fuel-saving stop/start systems, already in use on European manual-shift cars and being developed for automatics as well. The systems shut down the engine at rest and restart it when the brakes are released. There also will be new generations of more efficient multispeed transmissions.

BMW spokesman Matthew Russell says many other potential improvements can be made. “BMW has said there are several more percentage points of efficiency to be had from gasoline engines using technologies we know about today,” he says.

“For one, computer processing speed continues to increase, which allows us to do more in terms of real-time control of the engine.”

Russell points to BMW’s newest turbocharged M engine for clues as to what else can be done with more affordable versions.

“We like to use M cars as technology introduction vehicles, so that engine has a more advanced turbocharging system compared with this one.

“If you look at the differences between them – exhaust routing and turbocharger housing, for example – you can see some changes we might be able to make to an engine.”

But it’s always a balance between cost and benefit, he adds.

“With an M car, we have more freedom to do more on the cost side than we normally would,” Russell says.

We might call the challenge of continuous improvement to this less-expensive engine “CostEfficientDynamics.”