BMW AG 3L DOHC I-6
By Bill Visnic WardsAuto.com, Dec 20, 2006 9:09 AM

BMW AG has been scrambling lately to maintain its prime position atop the sport-sedan pecking order, as new and revitalized Japanese and U.S. competitors chip away at its Ultimate Driving Machine brand equity.

The cornerstone of that brand image is BMW’s famous – and famously smooth – inline 6-cyl. engine.

Shackled somewhat by the sensibilities of a European-market base that demands mainstream engines remain snugly sized, BMW watched in recent years as larger-displacement V-6s worked walloping horsepower advantages of as much as 70 hp over its 3L straight-six in sport sedans. Something had to be done.

The answer, launching last year in the U.S. market, is the magnificent N52 3L DOHC I-6, the 12th generation of the hallowed inline 6-cyl.

Using a raft of new power- and efficiency-enhancing tweaks, BMW narrowed the power gap with the half-liter-larger premium V-6s to the point where the engine’s intrinsic design advantages aren’t overshadowed by horsepower comparisons, alone.

Winning a Ward’s 10 Best Engines award for the second time in as many chances, the N52 returns BMW’s “standard” inline 6-cyl. to its rightful place as the exemplar of what a sport-sedan engine should be. Engineers baked in some materials intrigue, evidenced by the 3L straight-six’s high-tech magnesium-aluminum block – said to save about 22 lbs. (10 kg).

BMW wins 10 Best Engines award for second time with new-generation I-6.

Equally important, BMW engineers fitted the trick Valvetronic variable valve-lift mechanism to augment the VANOS variable valve-timing arrangement that already had been used in the previous-generation 3L inline 6-cyl.

The new fettling of the basic layout also delivered a key byproduct: an extra 500 rpm of engine operation. The redline now is a satisfying 7,000 rpm, and the new N52 feels robust and willing enough to run to 9,000.

Yanking the N52 up to 255 hp and 220 lb.-ft. (280 Nm) of torque – and unleashing the redline – makes for a mid-displacement performance engine without parallel. BMW’s new, ultra-tight valve control takes an engine that already was not short on excitement and adds a magnificent new level of throttle response and exhaust sound.

“This engine totally rips,” says one 10 Best Engines judge. “It’s ready to go at any rpm.”

More telling, perhaps, is what that hallmark inline 6-cyl. smoothness does for perceived performance: “255 hp,” says another editor. “It feels like more.”

And the new-generation inline 6-cyl.’s ability to deliver mid-20 mpg in the real world drives home the serious efficiency achievement gained with Valvetronic’s elimination of conventional throttle. It is an innovation other auto makers are preparing to emulate.

The sparkling performance and spectacular refinement at all engine speeds make BMW’s 3L DOHC I-6 a special experience, no matter how jaded the driver.

bvisnic@wardsauto.com