Engine and gearbox
Codenamed the S55, the 3-litre twin-turbocharged straight-six found in the current generation M4 puts out 424bhp, just an 11bhp increase over its predecessor, the M3 coupe. The big jump for the turbo’d motor over the old naturally aspirated V8 in the is in torque, which is up from 295lb ft at a peaky 3900rpm to a mighty 406lb ft from just 1850rpm.
As such, real-world straight-line performance is drastically improved, although the free revving nature and spine-tingling soundtrack of those motorsport-inspired engines in M-cars of old has been lost.
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Equipped with Competition Package, the M4’s power increases by 20bhp to 444bhp but peak torque stays the same. The extra power doesn’t dramatically change the attitude of the engine and, as the standard car’s performance is so strong, you don’t really feel the effect either. The Competition Package makes changes to the chassis too, and that’s where real improvements can be felt.
Where BMW deserves credit is in the work it has achieved with turbocharging. This engine is among the very best performance car turbo engines currently on the market. It boasts sharp throttle response and a willing top end. It easily can compete with the highly impressive 'Hot V' engine found in the C63 AMG and AMG GT.
In an effort to recreate some of that emotional engagement, BMW augments the sound of the new turbo engine by using the speakers within the cabin. The result, unfortunately, is not entirely convincing.
BMW offers buyers the choice between a six-speed manual gearbox and a seven-speed twin-clutch DCT unit. At a time when many manufacturers seem to be killing of their manual transmissions it’s great to know that M4 buyers can still opt for a stick and a pedal – although very few of them actually will.
The DCT ‘box is very effective, both in manual and auto mode. It can be a little clunky when left to its own devices, particularly when cold, but shifts are generally smooth and quick. In manual mode they bang in with a real intensity, responding immediately to the driver’s tweaks of the steering wheel-mounted paddles.
We do have some concerns over the way the drivetrain reengages, though, especially when shifting from third to fourth gear under full throttle load. When the new gear comes in, the torque delivery is so quick and abrupt that it can upset the rear axle and cause the tyres to break traction.
The M4 GTS’s engine is fundamentally the same as the standard M4’s, however, it makes 493bhp from its 2979cc straight-six thanks to the help of a water injection. The system alone doesn’t add horsepower, what it does is spray atomized water into the inlet to cool the gases and therefore allow even higher boost pressures which does increase power. The standard car’s water-to-air intercooler allows for a boost of 2.2bar, whereas the water injection allows the GTS’s boost to increase to 2.5bar.