At first, buyers will be able to choose between 194bhp and 255bhp 2.0-litre turbocharged petrol engines in the sDrive20i and sDrive30i variants respectively. But it’s the range-topping M40i, with its 3.0-litre turbocharged straight six, that represents the biggest threat to the Porsche 718 Boxster, our favourite convertible sports car for more than £40,000. With 335bhp and 369lb ft of torque, the M40i not only eclipses the entry-level Boxster (295bhp and 280lb ft) for performance, but it also sounds more exotic, thanks to its two extra cylinders.
Mind you, the latter point might be a little controversial, because it’s obvious that BMW has decided to channel some fake engine noise through the Z4’s stereo to help boost its aural charisma. This feels distinctly inauthentic and unnecessary, because the engine’s raw power speaks for itself.
Stretch your right foot and the big six-cylinder motor responds with virtually no lag, pulling hard from low in the rev range with a smooth, free-revving nature that the Boxster’s 2.0-litre engine can’t quite match. And although you’re limited to an automatic gearbox, keen drivers shouldn’t be disappointed, because BMW’s eight-speeder is one of the best around, delivering smooth, precise and reliable shifts on command.
But with 335bhp at your disposal, of course the Z4 feels quick in a straight line. What’s more impressive is the Z4’s new-found dynamic ability. Turn in to a bend and the car’s wide front end generates fantastic grip, while BMW’s trademark 50/50 weight distribution ensures the car has great balance throughout the corner. In terms of raw cross-country pace, it would certainly give an Audi TTS Roadster or Boxster a run for its money.
But despite having an impressive turn of speed, the Z4 is held back somewhat by its weight and sheer size. Indeed, when pushing on, you have to be incredibly accurate where you place the car due to its width. And although we were impressed with the Z4’s natural balance and grip, when the rear of the car does let go, it can be snappy and rather unwieldy. It simply lacks the same level of fluency as the relatively lightweight Boxster.