By Mark Elias
Wednesday, Sep 7th, 2011 @ 11:45 am
 
BMW breaks from its recent history of bringing in überly powerful inline six-cylinder and twin-turbo V8 engines with the return of a little 2.0-liter inline four-cylinder engine for the 2012 BMW Z4 sDrive28i.

A case of too little, or is it more like the "Little Engine That Could?" To find out, BMW hosted us in Northern California, where we had a chance to wring out the TwinPower Turbo-equipped hardtop roadster along legendary coastal roads as well as mountain twisties.

Hop in, bring your shades and let's go.

Sized right
We have enjoyed the BMW Z4 roadster since first experiencing it in 2009. At that time it had just undergone a redesign that essentially extinguished the flame-like DNA of designer Chris Bangle. In its place, we find a new, wider, lower, longer revision that makes the car just that much more comfortable. Now making news again, it is the first BMW platform to receive the new N20-designated 2.0-liter I-4 TwinPower Turbocharged engine on these shores.

The eighth iteration of a roadster to bare the BMW logo dating back to 1935, it is this second-generation of this era of Z4. Previous versions were usually made up of a coupe and convertible droptop.

This latest generation is the first to use a folding two-piece design that stows in the trunk in a quick 20 seconds. The result is a hit-two-birds-with-one-stone roadster that has the benefit of a hard top with extremely clean lines and loads of eye appeal from nearly all corners. The shortcoming of all this is the lack of trunk space once the Z4 is in sun-worshiper mode. Time to try out those Samsonite duffle bags, we say. On the other hand, competitors like the Audi TT, Lotus Elise, Mercedes-Benz SLK350 and Nissan 370Z offer little in the way of cavernous cargo hauling abilities, either.

Targeted
BMW engineers targeted certain parameters for the N20 inline four. Chief among them was the 120 horsepower-per-liter ratio that was achieved here. Maximum horsepower of 240 comes on at 5,000 RPM while they managed to realize the mill's peak torque of 260 lb-ft, at just 1,250 RPM. In our book, that's just barely breathing.

Seeking throttle response similar to a normally aspirated engine, BMW claims to have achieved its goal through the use of direct-injection and the company's Valvetronic variable valve timing controls, when combined with the single twin-scroll turbocharger. Hence the TwinPower nomenclature. The company boasts that the new 2.0-liter has 30 percent more torque than the naturally aspirated inline six-cylinder engine it replaces.

Separating the exhaust of one pair of cylinders from the other pair sends it (exhaust) through the exhaust manifold on a spiral path to the turbine. The low backpressure allows the exhaust gasses to pulse continuously through the turbine blades without a delay in throttle response. The net gain is elimination of turbo lag.

The N20 arrives standard with a typically refined, medium shift length 6-speed manual transmission. One of the silkier gearboxes available, its nicely spaced gates offered precision shifting without fatigue following a 300-mile drive from Northern California to Los Angeles. In other words, it doesn't beat you or your passenger up over the long haul. For those preferring to paddle their way through, an eight-speed automatic transmission with paddle shift levers is available.

In the field of fuel efficiency, the Z4's four-banger achieves a 20-percent increase over the naturally aspirated six-cylinder, when mated to the automatic. But leaving no stone unturned, BMW has added an auto start/stop engine management function that shuts off the engine at idle, say for example, at a stoplight, only to immediately re-fire as soon as the brake pedal is released. We must admit, though it is a bit disconcerting, feeling the engine re-firing when releasing the clutch pedal. We kept expecting a stall, but miraculously the system works. Trust the system. Though EPA ratings are still to be determined, the company estimates the 3,263 lbs. Z4 will achieve 32 mpg on the highway.

Bangle-free living
Construction of the Z4 continues as before, with an aluminum roof and electro hydraulic mechanism for smooth operations. As tight as Joan Rivers' face following one of her tune-ups, it handled well through the challenging back roads and grooved interstates leading to Westlake Village, outside of Los Angeles.

The long nose, short rear deck, GT-style packaging has had two years to mature since its last refresh. We still think it works very well. An optional navigation system with retractable screen appears at the top of the center stack. Visible in all sorts of light, including with the roof stowed, it was also the visual interface for operating the fourth generation iDrive.

It's a sporting life
Our Z4 tester was equipped with an available M Sport package that offered a bit of show and go. Included was the Adaptive M Suspension, aero body kit, 18-inch alloy wheels, M-badged steering wheel, shift knob and doorsills. Its seats were also swathed in Alcantara covering for added grip during excursions that required turns to the left""and the right.

Starting the Z4 is as easy as pushing a button. Once fired, the engine assumed an authoritative note that, while not intrusive, reminds you that you are driving a sports touring machine. Zero to 60 mph is achieved in 5.5 seconds, 5.6 if you opt for the eight-speed automatic. Remember when automatics added a second or so?

The Z4's Driving Dynamics Control button worked wonders and firmed up the ride for the mountain twisty turns we found on HWY 33 (Maricopa Highway) east of Santa Maria. Balance has improved due to the natural weight reduction from the lack of two extra cylinders. Now set at a distribution point of 47-percent front/ 53-percent rear, the DDC has more to work with. Switching from Normal to Sport mode causes a crisper throttle response, more direct steering operations, and more suspension firming over the standard setting. For really cheap thrills, cheap being relative, hit the Sport+ setting. It supplies all of the above, and turns off traction control, too.

Through peach orchards, pistachio farms and the occasional errant goat and llama, we experienced roads that challenged us, and our stomachs, with varying radius turns, tight switchbacks and the like. All the while, the four-banger under bonnet kept us informed, albeit with a higher pitched whine than we have been used to in other BMW cars.

This engine's note essentially said to us, "it's okay, I've got this.

Leftlane's bottom line
BMW is having a two-for-one sale. Buy the Z4 sDrive28i roadster, and get the hardtop coupe at no additional cost. The fact that the 2.0-liter turbocharged engine has the power of a six with the fuel efficiency of a four cylinder is the bonus. Like the story of the little engine that could, this little engine can.

BMW is charging about $1,000 more for the 2012 than it did for an equivalent 2011 with the six, and while the cylinder count is down, the fun factor is up.

2012 BMW Z4 sDrive28i base price, $48,650.

Words and photos by Mark Elias.