BMW 3.0L N55 Turbocharged DOHC I-6 update from January 2012

BMW is so good at inline 6-cyl. engines that just about every other auto maker has surrendered the niche to the Bavarians.

January 6, 2012

3 Min Read
BMW 3.0L N55 Turbocharged DOHC I-6

There comes a point while driving the BMW 335i when the mind pauses to take note of the propulsive power and the aural beauty of the N55 TwinPower inline 6-cyl.

It is a moment that makes the day a little sweeter, when all distractions and heavy thoughts melt away and the driver achieves oneness with an internal-combustion machine that is so much more than an assemblage of metal, plastic and rubber parts.

The experience can be fleeting or it can linger, like a laser light show that builds in intensity. What makes these moments memorable is the realization that the engine feels as if it is barely working. Who knew 1,500 rpm could be so exhilarating?

To cruise along effortlessly at 40 mph (64 km/h) at 4,000 rpm, only to realize the manual transmission is still in second gear, is to appreciate the supreme efficiency and unmatched flexibility of the N55.

“This is my favorite engine so far,” writes WardsAuto editor Byron Pope on his scoresheet of the 335i coupe midway through the competition. “It just pulls and pulls and has the best-matched exhaust note in the business.”

Fellow editor James Amend gushes further. “Let there be no doubt this is the best 6-cyl. on the market and probably the best overall,” he says on his scoresheet.

“Another homerun for BMW,” writes Editorial Director Dave Zoia.

This is the second consecutive year the direct-injection N55 lands among the Ward’s 10 Best Engines.

It faced respectable challenges from a new direct-injection 3.5L V-6 in the Mercedes C350 and from another returning winner, Volvo’s 3.0L turbo I-6, but the N55 pulled ahead with an average fuel economy that approached 25 mpg (9.4 L/100 km) during our 500-mile (805-km) evaluation.

The N55 is a pillar of BMW’s “Efficient Dynamics” powertrain strategy and uses a single twin-scroll turbocharger instead of the twin-turbo arrangement on the N54 I-6, which won Ward’s 10 Best Engines honors three straight years, from 2007 to 2009.

The twin-scroll housing properly separates the streams of exhaust gasses, allowing the turbocharger to build up pressure much faster than previous-generation turbochargers, mitigating turbo lag. 

The N54 makes more power, but the N55 achieves its peak torque earlier in the powerband while delivering better fuel economy, and that is the ruling principle as auto makers realign their portfolios to meet pending emissions requirements.

The N55 also does its business without a conventional throttle to regulate engine power but with the highly intelligent Valvetronic intake system, which uses an electric motor to continuously vary the amount of valve lift.

For the ’12 model year, BMW now markets an additional application of the TwinPower turbo I-6 on the larger 640i coupe and convertible. The coupe is just as fast as the previous-generation 650i, which offered a 4.8L V-8 capable of sprinting to 60 mph (97 km/h) in 5.4 seconds.

Oh, and with a city/highway rating of 23/33 mpg (10-7.1 L/100 km), the new 640i is 45% more fuel efficient.

BMW is so good at inline 6-cyl. engines that just about every other auto maker has surrendered the niche to the Bavarians.

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2012 10 Best Engines
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