Chances are, if you’ve been near a BMW dealership in the past few years, you’ve come across a car powered by the N55.  That’s manufacturing code for what BMW calls their TwinPower Turbo inline six cylinder engine.  That’s BMW-speak for a 3.0 liter engine with a single twin-scroll turbocharger and variable valve timing.  It can certainly get more complicated, but there isn’t any sense in explaining how it works.  It’s the results that matter.

What does all this technical mumbo-jumbo really mean for the driver?  300 horsepower, 300 lb-feet of torque, and a 7000 RPM redline.  Why is it important?  Because the N55 is available on every BMW model sold in the United States.  Here are it’s many iterations:

• 135i
• 335i
• 535i (535i GT)
• 640i (640i GC)
• 740i
• X1 xDrive35i
• X3 xDrive35i
• X5 xDrive35i
• X6 xDrive35i
• Z4 sDrive35i

With so many cars powered by the same engine, could the N55 be a “jack of all trades, master of none”?  We slipped behind the wheel of a number of BMW’s latest N55-powered models to find out.

335i xDrive

The 335i is a very confused 3 Series.  At the time of writing, BMW has released its F30 sedan, but is still producing the older generation E92 coupes.  Interestingly, this leads to a current dichotomy in fuel mileage.  The F30 sedan with stop/start and an 8-speed automatic is rated at 33mpg highway, but the E92 coupe with the old 6-speed automatic only gets 27mpg.   As it turns out with the release of the 4 Series Concept last week, the E92 will be the last 2-door 3 Series.  While that’s big news for most diehard Bimmer fans, the F30 3 Series and F32 4 Series will share engine options, so expect to add “435i” to the list of available N55-powered models.  That should also solve the mileage discrepancy.  Regardless, this is the car that the N55 was originally designed for so it should prove to be the most telling.

Flooring the 335i creates the aural combination of a straight six motor and a vacuum cleaner.  With that sound comes a slight hesitation as the xDrive system sorts the power out, and then its off to the races.  Peak torque arrives at just 1200 RPMs and stays with you all the way to 5000RPMs.  The variable valve timing and larger scroll of the turbocharger push the engine to its maximum horsepower output moments later, at 5800RPMs.  It’s as if the second stage of a rocket fired.  From there, it doesn’t take long to reach the 7000 RPM redline.  All this and you’ve just gotten into second gear.  The driver is at the center of involvement in everything the 3 Series does.  We hope the 4 Series continues that long-standing tradition.

The 335i isn’t the lightest car that the N55 powers.  The curb weight of 3759lbs is 320lbs heavier than the 135i. BMW rates the 335i’s 0-60 time at a conservative 5.2 seconds.  That’s quick enough to embarrass most potential competitors off the line.  The 3 Series chassis really allows the N55 to shine as a performance engine, both in speed and sound.  Yes, vacuum cleaner turbo included.

BMW 535i xDrive

The redesigned 5 Series is a smart looking ride.  It did away with much of the Bangle-era design cues that caused such discomfort for some fans.  The 5 Series has always been a great midsize luxury sedan.  It was never as nimble or precise as its little brother 3, but it rarely lost its roots as a sport sedan.  The 535i is a perfect example, sitting between the four-banger 528i and the V8 550i.  Here the N55 is pushing 4233lbs of German sheet-metal, and the difference is noticeable.  But that isn’t simply because of the extra weight.

The suspension has been softened and the steering has been numbed to prevent $6 coffee from becoming $6 coffee stains.  It’s by no means a disconnected experience, but having just gotten out of a 3 Series this car decidedly set on comfort.  Setting the adaptive suspension to Sport didn’t produce much of a result, either.

All of these facts seem lost on the N55, which manages to breath some fire into this executive saloon.  60mph arrives in 5.6 seconds, faster than the local coffee shop can serve your $6 coffee.  Unlike the 3 Series, the power delivery is smooth and nearly perfectly linear.  This car is no slouch, though it seems to try hard to disguise it.  Even the silky exhaust note seems distanced from the cabin.  You should have extra money for coffee with your fuel savings though, the 535i gets 30mpg highway thanks to its stop/start system and 8-speed automatic.

BMW X6 xDrive35i

Take an X5, put it on a diet and exercise routine, throw in some heels and a little black dress and you’ve got yourself an X6.  It’s a slimmer and sexier family hauler.  Of course, all this trimming takes its toll.  There’s one less seat, less rear headroom, and quite a bit less cargo space.  This SUV makes heads turn in envy.  I’ve spent a year around my family’s X5, and its gotten less attention in that time than the X6 got in one day.  Does that make it worth the $12,300 premium over the X5?  Its sexy, but it isn’t that sexy.

Unlike the 3 or 5, the N55-powered X6 is at the bottom of the engine pile behind the X6 xDrive50i.  The hefty curb weight of 4784lbs doesn’t help the X6’s case, needing 6.3 seconds to get to 60mph.  You’ll have your lunch money taken by a Porsche Cayenne S if you aren’t careful.  Despite this, the X6 is more fun to drive than the 535i.  There’s more feedback in the hydraulically-assisted system than the 5 Series’ electric system, so the driver is immediately more involved.  There’s also more engine and exhaust noise so the experience isn’t as isolated.  Wheel-mounted paddles, like those found in the 335i, are needed to drop the 8-speed automatic transmission down a gear and move the engine into its power band.  The X6 is a car that wants to be driven hard .  Again with the consequences, the X6 is rated at only 23mpg highway.

Verdict:

It’s interesting to be able to experience how different a single engine can feel across different platforms.  Ultimately, the N55 has proven to be immensely versatile and reliable.  It can successfully power anything from a small sport coupe up to a large SUV.  We can see why its been awarded a spot on Ward’s list of 10 Best Engines for 2012.  Most reports estimate that the upcoming M3/M4 will be powered by a turbocharged inline six.  If the N55 could possibly be anything more, its a great starting benchmark for that.

–Christopher Little