Turns out BMW Z4 Roadster is the first car to feature the firm’s four-cylinder engines on their return to the U.S. market. It will comes as the Z4 sDrive28i.

Back in February BMW announced they are bringing back four-cylinder cars to America with the new 2.0-liter TwinPower Turbo 4-Cylinder units. From Fall this 240 horsepower and 260 lb-ft of torque engine will become available for the Z4 offering the same power as the 3.0 liter straight-six but 20 percent better fuel efficiency.

Detailed specs of the Z4 28i and its pricing will be announced closer to launch, but for now check out some technical details on how this twin-scroll turbo four-banger works to achieve the best compromise between performance and economy:

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.