The new BMW i8 plug-in hybrid gives us an idea how it sounds like. The 4.7 meter long 1.5 liter three-cylinder unit cranks out 228hp at the rear wheels and a 129hp electric motor at the front axle. It produces a combined output of 357hp for a 0-100km/h in 4.4 seconds.

The video here shows an i8 accelerating from standstill to 130km/h. According to Bimmerpost:

"Our video shows the i8's gauge graphics as the car accelerates in Sport Mode, as well as providing a listen at the i8's raw mechanical sounds as it accelerates. While the production i8 will be equipped with Active Sound Design (enhanced interior sound technology), this particular car we're hearing has its Active Sound Design (ASD) disabled for testing purposes. ASD will not be able to be turned off by the driver in the production model (though BIMMERPOST members have foundworkarounds on other BMW models). ASD will sound different depending on the selected driving mode(s) - Sport, Comfort, Eco Pro."

"Another interesting feature we've learned is about the i8's exterior sound. The i8 will also feature Active Sound Design on the outside(as well as the inside of the cabin). The left exhaust pipe(dummy) is an external speaker used for the exterior sound projection while the right side is for regular (engine)emissions. Also the exterior ASD cannot be disabled."

Give it a listen in the video below: