BMW Z4 Roadster to be first four-cylinder offered on U.S. shores in decades

2011 BMW Z4 – Click above for high-res image gallery

Forced-induction, four-cylinder engines and small cars go together likes punch and pie. BMW understands this, and the automaker has officially announced that the Z4 is the first U.S. model to get its new turbocharged mill. This marks the first time in decades that BMW is bringing a four-banger to U.S. shores. Fans of the 2002, rejoice.

The BMW Z4 sDrive28i Roadster will serve up its engine bay for the new turbocharged 2.0-liter inline-four. Output is rated at 240-horsepower at 5,000 rpm and 260 pound-feet of torque, which arrives at just 1,250 rpm. Using a combination of direct-injection, BMW's Valvetronic intake management and a twin-scroll turbo allows the engine to produce V6 power with I4 efficiency. BMW expects to see a 20 percent improvement in fuel efficiency compared to the outgoing motor. The eight-speed automatic transmission will also certainly help the Z4 in the fuel economy fight.

No word yet on pricing or a date when we can see the turbocharged Z4 sitting in dealer showrooms. Click past the jump to read the full press release.

2011 BMW Z4 sDrive30i
2011 BMW Z4 sDrive30i
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[Source: BMW]
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BMW 4-Cylinder Engines Return to US in 2011 in the Z4 sDrive28i

New 2.0-liter turbocharged four-cylinder offers performance of a six

Woodcliff Lake, NJ – Following the announcement in February of the return of a 4-cylinder engine to the US BMW line-up, BMW today announced that the new 2.0-liter TwinPower Turbo 4-Cylinder will first power the Z4 sDrive28i that will arrive in BMW Centers this fall. Like the company's latest TwinPower Turbo 3.0-liter turbo inline-6, the new 2.0-liter engine will combine high-pressure direct-injection and BMW's VALVETRONIC intake control (hence the name:
TwinPower) with a forced induction system consisting of a single twin-scroll turbocharger.
With 240 horsepower and 260 lb-ft of torque, it offers more power and torque than BMW's
normally aspirated 3.0-liter inline-6 that it replaces in the Z4 sDrive30i.

The maximum output of 240 horsepower is achieved at 5,000 rpm, 1,500 rpm lower than
in the normally-aspirated 3.0-liter inline six. The peak torque of 260 lb-ft, comes on stream
at just 1,250 rpm. Not only is that 30% more torque than the aforementioned inline-6, it
also peaks 1,500 rpm earlier. The vigorous power comes on early and climbs steadily all
the way to redline.

The 4-cylinder engine with its all-aluminum crankcase is lighter and more compact than a
6-cylinder engine of equivalent power. The turbocharger is a twin-scroll system. The
exhaust streams leaving the two pairs of cylinders are kept completely separate as they
flow through the exhaust manifold and the turbocharger, taking a spiral path to the turbine
wheel. This configuration results in very low exhaust back pressure at low engine rpm, and
allows the energy of the exhaust gas pulses to be optimally managed and translated into
powerful rotation of the turbine blades, without a delay in throttle response.

The patented BMW VALVETRONIC system with seamlessly variable intake valve lift
control dispenses with the throttle valve system typical of conventional engines. Instead,
combustion air mass is controlled inside the engine, resulting in much faster response.
Pumping losses are kept to a minimum, making the engine more efficient.

The High Precision Injection direct-injection system also helps to improve efficiency.
Centrally positioned between the valves, solenoid injectors with a maximum injection
pressure of 200 bar (2,900 psi) precisely control the supply of fuel. The fuel is injected very
close to the spark plug, resulting in clean and homogeneous combustion.

The cooling effect of the injected fuel also allows for a higher compression ratio than might
otherwise be possible. This results in further efficiency improvements. In the Z4 sDrive28i,
we expect a fuel efficiency gain of approximately 20% over the naturally aspirated engine it
replaces when combined with the 8 speed automatic transmission.

Detailed performance and efficiency specifications will follow at a later date, but this is
clearly a new chapter in the story of BMW EfficientDynamics.

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