Why the comparison?
Because when Audi offered us an early UK drive of the R8 Spyder we couldn't resist bringing a Porsche 911 Turbo Cabriolet along for comparison. The R8 makes life pretty difficult for the 911, matching it almost exactly for price, while upping the ante on desirability for those in the market for an open-topped supercar. It's the first time in a while Porsche has had a genuinely direct rival for the Turbo Cabriolet, with the R8's power and performance right up with the 911's. Then there's the fact that VW now owns Porsche, and Audi is part of the VW Group. Intense sibling rivalry if you will.
How are they similar?
Both are big-power flagship models in their respective line-ups; both feature four-wheel drive and in this test they're manual cars with six-speed transmissions. Either can be had with automatic gearshifts, but to choose them with two pedals and paddle-shifters is to rob these open-top cars of a good portion of their driver appeal.
The R8's V10 delivers 518bhp, which betters the Porsche's 500bhp. The turbocharged Porsche fights back with a more substantial 479lb.ft of torque compared to the Audi's 391lb.ft. Against the clock the 911 is a bit faster, reaching 62mph in just 3.7 seconds, the Audi taking a further 0.4 seconds to record a 4.1-second time in the benchmark sprint.
Audi quotes a top speed for the R8 Spyder of 194mph. Porsche claims its 911 Turbo Cabriolet is 1mph slower at the top end, but Porsche's top speed figures tend to be on the conservative side. These cars are within a few thousand pounds of each other too, with both commanding a price around £112,000 - that likely to be a good bit more with a few choice options such as carbon ceramic brakes.
How do they differ?
On paper the R8 Spyder and Porsche 911 Turbo Cabriolet are obvious rivals, but for all the similar numbers there are a lot of differences. Chiefly, the engines. Audi has chosen a naturally aspirated 5.2-litre V10 unit to power the R8 Spyder. Porsche has four less cylinders and uses variable vane turbochargers to allow it to deliver its performance. The Porsche engine is also a boxer engine, positioned behind the rear axle on the 911 Turbo. The R8's V10 is positioned a bit more conventionally - for supercars at least - being in a mid location behind the passenger compartment, but still in front of the rear axle.
The engine position in each affects the interior architecture, the Porsche's smaller and unconventional engine placement allowing the 911 Turbo to offer a pair of rear seats - albeit small ones. The R8 Spyder is a strict two seater, with little concession to practicality except for a small space under the front bonnet. In comparison the 911 is positively capacious, with its small under bonnet luggage compartment complemented by that surprisingly useful rear seat area.
Forget the technical details though; for all the similarities and minor differences the R8 Spyder and 911 Turbo Cabriolet couldn't feel more dissimilar. Jump into the Porsche straight from the Audi and you're immediately struck by how uninteresting and devoid of flair the 911's interior is. Sure, it's solid and familiar, but for north of £100,000 it's just not special enough. Despite that extra space behind you the 911 feels smaller, physically and behind the wheel.
It's the gaping chasm between them on the road that's most obvious though. The R8 Spyder's engine is more sonorous, the tune from its tailpipes immediately more exotic than the rather subdued note emanating from the 911 Turbo. There's more steering feel with the 911, but the R8 is the car that delivers more to drivers at lower speeds.
With experience of both at higher velocities we know the 911 Turbo can be sensational, but it needs to be at track speeds to deliver its thrills. The Audi by comparison is so much more visceral, far more exotic and special feeling on the road at normal speeds; it makes the 911 Turbo feel pretty ordinary. Even the R8's manual shifter is an occasion, each change of ratio signalled by a metallic clicking though its exposed aluminium gate. The 911's shift is arguably better in its action and precision, but it's far less of an occasion.
So which one would we have?
The 911 Turbo Cabriolet certainly isn't ordinary; it's an exceptionally competent, involving and devastatingly fast open-topped supercar. Except in this company it's made to feel uneventful; the Porsche's restraint in its exterior styling and disappointing interior are brought sharply into focus when the R8 Spyder arrives. The Audi is just so much more interesting, more of an occasion more of the time and easier to get the most from on the road at legal speeds.
That's not to say it's a clear-cut win for the R8 Spyder: if we were buying a car like this to use everyday then the Porsche's virtues of relative discretion and greater practicality could make it the more appealing choice. But open-topped supercars aren't about being rational, so if a weekend toy were the key reason why to buy we'd have the Audi every time. And we never thought we'd say that.