Posted on 06 October 2008.
The car looks just like a normal S5, but according to photographer it did not sound like S5. Also the front bumper is different with bigger air intakes giving it away that is a test mule for the RS5.
RS5 will be competing with BMW M3 and Mercedes-Benz C63. RS5 just like other RS models is developed by Quattro, Audi’s in house performance team.
RS5 will feature Audi’s quattro drive and a 4.2-liter V8 that powers current RS4. Power will be at 450 hp (S5 has 354 hp).

TYPO: S5 has 354 HP
thanks for the correction Wes.