The Audi TT has always been a bit of an anticlimax for performance car fans; it’s a car that’s never been quite as great to drive as it is to behold. But Audi’s got a sea change in store for its smallest coupe and cabrio siblings. Three new sporting models arriving before the end of decade will inject a massive dose of driving appeal into the TT’s mix – a Cayman-rivalling TTS, a BMW M3-chasing TTRS, and an all new twin turbo TT diesel – and we’ve got the documents to prove it.

Coming in Summer 2008: TTS

The first of Audi’s new TT performance trio to arrive will be a new four-cylinder turbo model running a version of the Audi S3’s four-cylinder turbo engine, and with a UK price tag of around £33,000 – the 266bhp TTS.The arrival of this car has been leaked via the internet this week, in a product planning document intended to be kept secret by Audi’s German dealers. In it are contained the release schedule, the power output, the transmission options and the name of the new car.The TTS will be launched in Germany in the second quarter of 2008. It’ll be identifiable by its quad tail pipes and its extended front bumper and more aggressive air dam (see our spy pictures). It’ll be available with either a six speed manual gearbox or an ‘S-tronic’ DSG automatic transmission, and as either a coupe or a roadster. All versions will get Quattro four-wheel drive.Audi will aim for the budget end of the performance coupe market with this car; it’s their answer to the Nissan 350Z, the standard Porsche Cayman and the new BMW 135i, leaving the likes of the new BMW M3 coupe and the Porsche Cayman S to it’s faster five-pot brother, the TTRS.

Here in early 2009: TT TDi

Joining the growing ranks of sporting diesel coupes in early 2009 – and coming as a direct rival to the new BMW 123d coupe – will be a twin-turbo diesel version of the TT. Our spies have only this week caught the first development prototype of this car doing cold weather testing. It looks like an ordinary TT from the outside, but don’t be fooled; it’s the label on the car’s dashboard that gives its origins away.Under the bonnet of this new sporting oil-burner is the VW Group’s new twin-turbo version of its 2.0-litre common rail diesel engine. This engine has yet to appear in any VW Group product – it’s likely to find an application next year, possibly under the bonnet of the new VW Coupe – but it’ll certainly be a big draw for potential buyers of the TT, as it packs 202bhp, almost 300lb ft of torque, and should also make for a TT capable of a 40mpg average fuel economy, and less than 150g/km of CO2.Likely to be offered in Quattro guise only, the new diesel-powered TT’s excess of torque should ensure performance on par with its petrol-engined 2.0-litre sibling. Nothing’s official but 0-62mph should be possible in under 6.5secs, as should a top speed around 150mph. At the same time, improved fuel consumption will give the new car a greater range on its 55-litre tank.One drawback of the new engine’s heady torque reserve, however, is the inability of Audi’s existing six-speed S-tronic double clutch gearbox to handle it. While the prototype pictured here runs a six-speed manual, Audi has admitted it is already working on a newer seven-speed S-tronic gearbox that can be mated with engines producing up to 370lb ft.The TT TDi should be priced from around £27,000.

The hottest TT of all: TTRS

Before the end of the decade we’ll see the ultimate performance version of the Audi TT – a car that many expect to revive the spirit of the short-wheelbase Audi Sport Quattro S1 in more ways than one – the TTRS.This car will be a TT like we’ve never seen before. It’ll be priced at around £45,000 in order to undercut the new BMW M3, and to put plenty of clear air between it and the forthcoming, £55,000, 414bhp Audi RS5. And it’ll earn that price tag with a cleverly set-up, rear-biased Quattro four-wheel drive system, with twice as much driver involvement as any other TT, and with a 2.5-litre five-cylinder engine producing a generous 343bhp – enough to crack 62mph in under 5.0secs and to show a clean set of heels to a Porsche Cayman S.Quattro GmbH has been given the task of developing this rocketship TT, and although nothing’s set in stone yet, it’s likely to throw out Audi’s ‘Magnaride’ dampers for more performance-oriented alternatives, to discard the car’s rear seats in order to save weight, and to do a major overhaul of the TT’s four-wheel Quattro drivetrain. The TTRS’ will have wider tracks than the standard car, run 20in alloy wheels and will borrow the RS4’s carbon ceramic brake discs too.And then there’s the TTRS’ engine. As part of the same leak that exposed the TTS came a technical drawing from Audi that gives us more information on the RS’s 2.5-litre motor. It’ll be both supercharged and turbocharged, becoming the second motor in the VW Group’s line up to wear the TSI ‘twincharger’ badge. And Audi sources say it sounds every bit the modern successor to the original Quattro’s warbling five-pot.For a guide to the finished TTRS’ looks, see the TT Clubsport concept. That concept car, however, was a roadster (the road car should be coupe-only), and only had 300bhp. Here, then, is an example of production car reality outstripping show car largesse. And that doesn’t happen very often.

Matt Saunders and Greg Kable