First the good news. Fans of six-cylinder BMW engines may have been dismayed to realise that the creamy naturally-aspirated straight-six is not long for this world - at least in terms of the blue-and-white roundel. The constant downward pressure on emissions and fuel consumption is forcing BMW, like every other carmaker, to make its motors ever-more efficient. And that means turbocharged fours are in, and six-pots are out.
Some bits are good, others not so much
We mentioned good news? Oh yes - said turbocharged 2.0-litre four is a corker, in the Z4 at least. There are two versions available for BMW's folding hardtop coupe-roadster thingummy: a 184hp version, and this, the 245hp option in the Z4 sDrive28i. The new motor, courtesy of such tricks as the variable camshaft control system double Vanos and the fully variable valve control system valvetronic (not to mention a twin-scroll turbocharger) is just 13hp down on the old sDrive30i, despite giving away two cylinders.
It's also got 29lb ft more torque than its predecessor, 258lb ft available between 1,500rpm and 4,800rpm, which not only gives a decent turn of outright speed (0-62mph in 5.7 seconds and a limited top speed of 155mph), but also provides some fairly serious and easily accessible real-world poke. It's a crisp, linear motor, too, with sufficiently sharp throttle response and enough eagerness all the way through the rev range to feel distinctly un-turbocharged at times. And all that's in conjunction with CO2 emissions of 159g/km and an impressive official combined fuel consumption figure of 41.5mpg. Which is suitably green.
No need to feel short-changed engine wise
BMW is also very conscious of the lack of aural merit relative to its older six-cylinder offerings. As a consequence it has come up with an electronic sound generator, to give it a better bass and baritone note both at idle and in the main 2,500-3,500rpm rev range. The result won't fool you into thinking you're driving a six, but its eager gurgle sounds pleasant enough.
So that's the good news. Unfortunately this is also followed by some bad news: the engine's comfortably the best bit of the Z4. It's not the build quality or design that's the problem - it's all well screwed together, has plenty of kit and looks sufficiently sporty, if a little awkward from some angles. It's the handling that's the issue.
Damping takes sheen off the handling
And the main issue with the Z4 – much as with the Merc SLK – is that it doesn’t really seem clear what it is trying to be. Is it a relaxed boulevardier? It can’t be, because the ride is too tough and fidgety, the steering too sharp, and its general demeanour a little too lairy. A proper foucused sports car, then? Er, nope, because even though there’s a stiff-ride, the Z4 often feels under-damped, making comfortable – or even rapid – progress over rough B-roads pretty much an impossibility.
Essentially, it just doesn’t hang together as a dynamic package. And that’s a shame, because despite the lovely engine, a spot-on driving position with well-positioned pedals and a lovely six-speed manual gearchange (the eight-speed ZF auto is also an option), that unresolved chassis is a bit of a deal-breaker. Especially when there’s a new Porsche Boxster on the way...
BMW Z4 SDRIVE28I
Engine: 1,997cc 4-cylinder, turbo
Power (hp): 245 @ 6,000rpm
Torque (lb ft): 258 @ 1,500-4,800rpm
0-62mph: 5.7 sec
Top speed: 155mph
MPG: 41.5 (NEDC combined)