BMW Capping Size

Fans of the “Ultimate Driving Machine” had better be satisfied with the size of BMW AG's current engines. They won't be getting any larger, says the auto maker's powertrain chief.

“The time to increase horsepower by increasing displacement is over,” says Klaus Borgmann, senior vice president-powertrain development.

Future performance increases for BMW's volume-production engines — he excludes the low-volume, ultra-high-performance engines developed for vehicles sold by its Motorsports in-house tuning division — will be achieved via advances in technology and new designs, not larger size, Borgmann says.

The twin-turbocharged 3L inline 6-cyl. BMW unveiled at the recent Geneva auto show indicates the company's intended powertrain-development direction, he says. More than 50% of the vehicles BMW sells worldwide are powered by inline 6-cyl. engines, and turbocharging its stalwart powerplant yields about 302 hp and 295 lb.-ft. (400 Nm) of torque — figures that match or exceed high-performance V-6s from BMW's Asian and North American competitors that typically are a half-liter larger.

At 302 hp, the twin-turbo DOHC I-6 is 47 hp stronger than the most powerful version of the same engine in normally aspirated form. But equally important, Borgmann says, is the 295 lb.-ft. of torque, a 75 lb.-ft. (102 Nm) jump that enhances engine flexibility and response, he adds, without any meaningful increase in fuel consumption because the turbochargers do not generate high boost levels.

Fuel consumption and emissions are the key reasons BMW has nixed future size increases for its volume engine families.

Borgmann says BMW's new turbocharged inline 6-cyl. also will employ direct (in-cylinder) fuel injection, a complementary technology seeing rapidly growing fitment for turbocharged engines to aid economy-enhancing downsizing.

The two technologies are so complementary, in fact, that Borgmann does not foresee direct injection seeing much future use for gasoline engines unless it is coupled with turbocharging.

A growing number of premium and performance 4- and 6-cyl. gasoline engines are combining the two systems because direct gasoline injection (DGI) has a low-rpm torque-enhancing effect.