For a long time, the C6 RS6 was Audi’s most powerful car. The R8 didn’t surpass its absurd 571bhp output for years, and although faster, the C7 RS6 wasn’t as potent.
The reason? In a moment of madness, Audi decided the latest version of its super estate/saloon really ought to have a V10. With two turbochargers. And this wasn’t even the first A6 to be gifted with 10 cylinders - the A6 and A8 had been tooling around with V10s (albeit minus the turbochargers) for two years by the time the C6 RS6 landed.
This was a bonkers era for the VW Group, with all sorts of ambitious and very often loss-making projects instigated at the behest of then-boss Ferdinand Piech. The sheer amount of high-calibre silliness going on at the time defies belief when you look back - the Q7 V12 TDI, the Phaeton and the Veyron all came into being around this period.
Stuffing a supercar engine with additional boost into an otherwise humdrum executive car, then, was par for the course. And we mean supercar engine - rather than upgrade the 5.2-litre unit in the S6 and S8, the RS6 borrowed the 5.0-litre powerplant from the pre-update Gallardo. Power went from 493bhp to 571bhp, while the torque shot up from 376lb ft to 479 and while you have to spin the V10 in the Gallardo up to 4250rpm to feel that peak torque figure, the RS6’s full torque delivery is available from just 1500rpm.
Peak power comes in lower, too - 6700rpm instead of 8000, with the rev limiter cutting in at 7000. Inevitably, the character of the unit is entirely different. It’s the punchy mid-range you’ll generally use to get yourself around at speed.
A lot of modern turbo engines with this kind of power seem to quickly wake up at 2500 or 3000rpm, but the C6 takes a little longer to get into its stride. It ramps up slowly from 3000 to 5000rpm, with the speed building at a particularly alarming rate past that point. The six-speed ZF automatic meanwhile can’t match the immediacy of a modern transmission, but it shifts briskly enough.
While certainly effective at firing you down a road awfully quickly, the RS6 doesn’t provide an especially thrilling soundtrack. Even with the advent of noise-sapping petrol particulate filters, exhaust technology is far more effective these days at letting engines sound their best within noise regulations.
The C6 RS6’s exhaust is…just an exhaust - no fancy active butterfly valves and the like here. Inside and out, it’s hard to tell it’s even powered by a V10, such is its muted nature. Much of the time, it could pass for an inline-five.
The irony is, more drama is served up by the - in theory - less interesting twin-turbo V8 found in the new RS6, which we had at our disposal the same day as Audi UK’s heritage fleet C6. Unlike the C6’s V10, which only ever powered one car, this 4.0-litre V8 engine is used across multiple models and brands, but who cares about the lack of exclusivity when it’s this effective?
The 592bhp C8 gets going a lot earlier - 3000rpm and up, it’s an utter beast. There’s more noise to be heard for both the driver and the bystanders they are blasting by, and when it’s time to swap a cog, a far more advanced eight-speed automatic is ready to chuck in the next gear.
This stark contrast continues in the corners. The C8 can be barreled into corners with abandon, with an active anti-roll bar, rear-wheel steering and trick air suspension working together to make the car feel like it weighs a whole lot less than 2.1 tonnes. Try to take a bend with a similar kind of enthusiasm in the C6, and it sort of gives up.
The front end in the older car is very keen to push on into understeer, and the most you’ll ever get from the rear is the gentlest of nudges. The C8, by contrast, is much happier making things interesting at the rear axle, no doubt aided by the five-degrees of steering angle it can give back there. The all-wheel drive systems in both, it’s worth pointing out, feature Torsen centre differentials and have the same general 40/60 front/rear split.
Another trump card the current RS6 has over its larger-engined predecessor is air suspension. There’s a much greater bandwidth in this system compared to the C6’s adaptive dampers and steel spring setup - the newer car is more cosseting in Comfort mode and more composed in Sport.
The elder of the two does claw back some ground with its understatement - both inside and out. Yes, the C8 looks brilliantly unhinged, but it lacks the grace of the C6. Lightly widened arches aside, it could easily be mistaken for a boggo diesel A6, and there’s an appeal to that kind of subtlety. It’s the same story inside - the the C6 has a peak Audi cabin, with a solid, classy space that makes the C8’s interior seem somewhat try-hard.
Overall, though, the C6 RS6 is oddly underwhelming, particularly in the presence of its modern successor. We can’t be too down on it, of course - it’s just an effective demonstration of how far the game has moved on since 2008. Back then, fast estates were just that - they didn’t try their best to be as exciting as a supercar. Yes, the RS2 we tried not so long ago - the ancestor to both of these RS6s - did manage to thrill in a modern context, but a lack of refinement relative to C6 helps massively.
Much like the Q7 V12 of the same era, the C6 RS6 is a car you respect for the technology and the general ridiculousness of the concept, rather than the way it makes you feel. That said, I’d love to try one with a ruder exhaust…