in the UK by Cosworth Technology (now known as MAHLE Powertrain). However, the 2005 season proved difficult due to performance restrictions imposed on Champion Audi Racing by the Sports Car Club of America (SCCA), with Champion deciding to run a different wheel diameter, and the trade-off was reducing boost pressure. C6 (Typ 4F, 2008–2010) The second-generation RS 6, later called the Audi RS 6 5.0 TFSI quattro (''Typ'' 4F) was based on the Volkswagen Group C6 automobile platform and was launched in September 2007 at the Frankfurt Motor Show. With factory production starting in December 2007, it was available in Europe from the same date, and began to be exported elsewhere in 2009. The total production run of the C6 RS 6 was 8,000 units, with 6,500 of these being Avants and the remainder saloons. The RS 6 was not available in North America, leaving the Audi S6 as the top performing trim there. (The unpopularity of wagons made it unlikely that the RS 6 Avant would be imported, and although it had been rumoured that the RS 6 sedan would be offered in the United States, nothing came of this as the RS 6 importer could not clear US regulations). Production of the C6 RS 6 ended in the third quarter of 2010. The RS 6's V10 engine produced at 6,250 to 6,700 rpm and of torque from 1,500 to 6,250 rpm, and more than BMW's 5.0L V10. , the RS6 was Audi's single most powerful car ever, and positioned the car ahead of its closest competitors, the BMW M5 and the Mercedes-Benz E63 AMG in terms of engine output, both of which have naturally aspirated engines. However the estimated price of the RS 6 sedan in 2010 was $160,000 USD (another source quotes $126,000 USD in 2009, making the RS 6 perhaps too expensive for the United States market) which set it apart from the performance variants of other executive cars: the MSRP of BMW M5's was $85,700 USD, of Mercedes-Benz E63 AMG's was $87,700 USD, and of Audi's own S6 was $78,025 USD. Official performance figures for the Avant: 4.6 seconds for the 0- sprint, 12.7 seconds 0-, and top speed is electronically limited to , with a factory option to de-restrict the top speed to . In standard form, CO2 emissions are rated at 333 g/km. The saloon reaches 0- in 4.5 seconds. C6 bodywork and