This week, BMW announced the return of a four-cylinder engine to the US line-up for the first time in since 1999. Like the company's latest 3.0-liter turbo inline six, the new 2.0-liter engine will combine twin-scroll turbocharging with high-pressure direct-injection and VALVETRONIC intake control. With 240hp and 260 lb-ft of torque, it offers more power and torque than BMW's normally aspirated 3.0-liter inline six! The new engines are scheduled to arrive later in 2011.
Peak horsepower is achieved at 5000 rpm, 1500 rpm lower than in the normally-aspirated 3.0-liter inline six. The peak torque comes on stream at just 1250 rpm - 1,500 rpm earlier and 30% more torque than the inline six.
The design features an all-aluminum crankcase. It's lighter and more compact than a six-cylinder engine of equivalent power. The exhaust leaving the two pairs of cylinders are kept completely separate as they flow through the manifold and the turbocharger, taking a spiral path to the turbine wheel. This configuration results in low back pressure at low engine rpm, and allows the energy of the exhaust gas pulses to be 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 2900 psi 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.