Speed Week: BMW M4 vs Porsche Cayman GTS

These are the ones that everyone thinks they know - the cliched, sideways-everywhere BMW M car, and the equally cliched, universally brilliant Porsche Cayman. But things are different this year. Sort of... we'll get to that later. The
big news is that BMW's core M car is no longer an M3 - the coupe M is now called the M4, while the four-door variant retains the iconic moniker. And that's not all - the straight-six engine makes a welcome return, but now it's turbocharged. Twin-turbo'd, to be precise, with 425bhp and 405lb ft, a clever anti-lag system and improved CO2 and mpg. It's an M car for the modern world, outpacing Ms of old, but with a slightly more planet-friendly, efficiency-led and turbo-fed motor under the bonnet

Photography: Mark Fagelson

This isn't any ordinary Cayman, either. It's the brand-new GTS (with a stiff price increase of £6,614 over the S): the first time the legendary Gran Turismo Sport badge has been stuck on the backside of the humblest Porsche coupe. As ever with Porsche, the badge isn't just a cosmetic addition: power is up by 15bhp to 335bhp, torque increases by 7lb ft to 280lb ft, and the GTS comes as standard with the Sport Chrono package - Stuttgart's performance-enhancing bundle that includes a clever system of active engine mounts which help stiffen the car's resolve when you're really on the doorhandles.

Boy, does it feel instantly right when you climb in. There's little surprise in the GTS cabin, but the happy flipside is the subconscious way you can get in and go. Turn the key, drag the PDK gearlever back into Drive, press every Sport button, and then mash the throttle. The GTS is addictively simple to drive, and you're confidently on the pace within two corners. So far, so very much normal service. What's surprising is the dose of humour the GTS's new sports exhaust has added: the Cayman now pops and crackles with the best of them. It's a Cayman with extra character.

The rest is as predictably brilliant as ever. And before you roll your eyes, the truth is that the GTS is superb on the track. There simply aren't any huge flaws. Rapier-sharp throttle response, perfect chassis balance, excellent PDK and point-and-shoot steering, a seat that grips in all the right places - how does Porsche manage to build a car that feels so right for so much of the time? The only half-criticism is that the chassis always feels like it can handle more power. But that's only because it's so damn good. It's all so natural.

Which can't be said about certain aspects of the M4. The BMW literally feels more forced, thanks to the turbos. And while the anti-lag system is seriously clever - effectively, it artificially maintains a minimum of 120,000rpm in the turbos so you've got instant boost whenever you want it - it never feels quite as reactive as the naturally aspirated Porsche. Cunning tech, but you're still aware of it.

Unlike the Cayman, there's no point in revving it all the way to the (admittedly high) 7,600rpm red line. There's all the punch you'll need below that, and there are no hidden sonorous gems waiting for you above five grand. It will happily rev, but better to sit back, relax and let the turbos take the strain in the mid-range. Relax? In an M car? This is definitely a brave new direction.

Not that the BMW isn't without other strengths. The brakes, for instance, are superb. This M4 has the optional (£6,250) carbon-ceramics, and, unlike other similar set-ups, there's plenty of bite and feel right from the moment you hit the pedal. Combined with the M4's prodigious front-end grip, it's eminently easy to get the nose tucked in, sniffing out the apex. A handy trait when a car steps sideways as readily as the M4. Watching The Stig adopt his favoured pose of tyres-a-smokin', the BMW looks absolutely stable, gliding through the corner as smoothly as water flowing over glass. Suddenly we're back in traditional M car territory - and it's easy to get used to the way the M4 scythes around a sweeping curve.

The M4 certainly flatters. But, bluntly, it doesn't reward as much as the Cayman, and certainly not on the track. The steering feels artificial compared with the Porsche's, despite both having similar electro-mechanical set-ups, and you don't get as much feedback from either it or any of the other seat-of-pants metrics. It's comfortable, though - and you can see where BMW is going with it.

Which means the Cayman feels the happier of the two at Castellolí, but there's one massive niggle that I can't shake. The GTS hasn't moved the game on as much as we'd hoped it would - oddly, and perhaps perversely, the stock Cayman is almost too good. It's the default, sensible choice, but somehow no one gets out of the little Porsche with any burning passion for it. It's all thoughtful nods and slightly weary respectability. The BMW, on the other hand, is somewhat more flawed on track but eminently more intriguing. It requires more analysis. And while it's not as epic-feeling pounding a circuit, it feels like it might come into its own on the road. Which is handy, because the next part of TG's Speed Week happens to contain...