SPY PICS: BMW M4 Coupe and Convertible

The imminent arrival of the BMW M4 Coupe has been confirmed by these new spy photos, revealing the car is undergoing final production testing before being unleashed on public roads.

Wearing only minor camouflage and exposing the M Division's iconic quad exhaust system, the spy photos of both the coupe and convertible versions of the M4 leave little to the imagination as to how the new car will look.

Replacing the BMW M3 Coupe and expected to ditch the current 4.0-litre V8 in favour of a turbocharged six-cylinder engine, the M4 Coupe is expected to be revealed this week in concept form ahead of the production car's debut in early 2014, potentially at the Geneva motor show in March.

Even more interesting is an official video released by BMW's M Division this week (see below), which provides an aural sample of the car's exhaust note for the first time -- and is the best proof yet the car will not exploit a V8.

Rather than a lumpy V8 burble, the exhaust note has a flatter tone, almost certainly the sound of a turbocharged inline six-cylinder engine.

BMW's 4.0-litre V8 is being ditched in favour of a smaller, more efficient engine to meet increasingly stringent emissions regulations in Europe, and reflects a similar move by Mercedes-Benz which is switching to smaller capacity turbocharged engines for the same reason.

The new M4 Coupe and M3 sedan six-cylinder engine is likely to output around 330kW, up from 309kW, to more capably combat the Mercedes-Benz C 63 AMG's 336kW output. Expect a big torque boost too, potentially beyond 500Nm of twist.

Expect several carbon-fibre components to help keep the M4 Coupe's weight to a minimum, and the latest driver aids to ensure make even modest drivers look fast.