Audi is close to signing off the hottest-ever TT, a range-topping RS model with 350bhp and aimed at the Porsche Cayman S and BMW M3.

Although it won't be a carbon copy, the TT RS is likely to take styling cues from the TT Clubsport concept (see gallery) that appeared earlier this year. Power for the hottest TT will come from a turbocharged version of a 2.5-litre five-cylinder petrol engine currently used by VW in US versions of the Jetta saloon.

With high-pressure turbocharging, peak power is lifted from 150bhp to 350bhp, a heady output of 140bhp per litre.According to an insider who has heard the TT RS, Audi's hot new coupe makes "a fantastic noise, just like the original Quattro".

According to another insider, the RS is close to the production go-ahead, but still awaits the final rubber stamp from Audi bosses. Should it be confirmed, Audi is said to be looking at a launch date sometime in 2009. 

In the TT, the performance ought to be strong, too. A top speed limited to 155mph is easily within reach, while 0-60mph ought to be down to five seconds. 

Power might be 50bhp down on the 400bhp BMW M3, but the TT RS will make up the deficiency with a lighter kerb weight, with the potential for a power-to-weight ratio of around 250bhp per tonne, and a whole heap of turbocharged torque. 

It's likely that the 350bhp TT RS would only be offered as a coupe, as the inherent strength of a car with a roof would be neccessary to deal with the forces generated during cornering, acceleration and braking.

A second hot TT, the S, is also in the pipeline. Unlike the RS, this model has been signed off and will be launched next year. Featuring the S3's 261bhp, turbocharged four-cylinder engine, the TT S will become the hottest TT model next year until the RS takes that spot in the range.