BMW 4-Cylinder Engines Return to US in 2011 in the Z4 sDrive28

As anticipated by BMWBLOG, the first four-cylinder BMW to return to the United States is the Z4 sDrive28i Roadster. Introduced today at the BMW press conference in NYC, the Z4 in Atacama Yellow is powered by the all-new N20 four-cylinder TwinPower engine.

Like the Z4’s last TwinPower Turbo 3.0-liter turbo inline-6, the new 2.0-liter engine will combine highpressure direct-injection and BMW’s VALVETRONIC intake control. 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 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 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.

BMW has yet to release the official fuel consumption numbers, but we know that the heavier X1 28i has an average MPG of 29.7, so we expect even better numbers in the Z4.

No details either on whether the price of the Z4 will be increased.

[Photos: Christiaan Conover ]