Like all M-cars down through the years, it is the engine that moulds the driving experience of the M4 coupé more than anything else. And it is here where the new twin-turbocharged six-cylinder unit both impresses and disappoints. At start up, it sounds remarkably similar to the twin-turbocharged V8 from the M5, with an odd diesel-like chatter to the engine and a raspy exhaust note. Thankfully, it improves as you select first and move off.
Predictably, the single biggest change over the M3 coupé is in the delivery, which couldn’t be any more different than before. With all that torque concentrated low down, there is substantial shove from little more than idle. This results in outstanding flexibility across a much wider range of revs, making it much better suited to stop/go city driving than its predecessor.
Just don’t count on the same razor-sharp throttle response as before when the road opens up and you get to put your foot down. The inherent qualities of the forced-induction engine mean the initial pick-up is a lot less rabid than with the old naturally aspirated unit owing to a fleeting moment of lag as the two turbochargers spool up to full boost. But once they do, the in-gear shove is uncompromising.
Still, there's no need to pile on the revs in an attempt to tap into the deep seam of performance offered by the new engine. You merely flex your right foot in a suitable gear and the engine obliges with truly muscular properties. The resulting rush of acceleration is spectacular, particularly between 3500 and 5500rpm where the M4 coupé feels to be at its strongest.
Inevitably, though, it lacks the outright aural intensity of the unit it replaces, despite the inclusion of Active Sound Design, which reproduces the sound of the M4 coupé’s new six-cylinder through the audio speakers at various volumes and frequencies based on engine revs, throttle load and speed.
With two mono-scroll turbochargers, variable valve timing and continuously variable camshaft control, it revs quite freely, extending to 7600rpm before the onset of the limiter. This is quite high by turbocharged engine standards, but 600rpm less than the old naturally aspirated engine achieved.