<P> All Audi "S" models are equipped with Audi's' trademark' quattro four - wheel drive system as standard . Unique internal combustion engines, along with larger, more powerful brakes, stiffer suspension systems, additional exterior body styling, and carbon fibre interior trims set them apart from their related "siblings" of their respective model range . </P> <P> In the past, some Audi S models competed directly with BMW M and Mercedes - AMG models, such as the B6 Audi S4 4.2 FSI versus the BMW M3 and Mercedes - Benz C32 AMG . Since 2010 however, Audi S models have been positioned more as optional engine trims . For instance the base Audi A4 (B8) engine is the 2.0 TFSI turbo four - cylinder, and with the discontinuation of the 3.2 FSI V6, that makes the Audi S4's 3.0 TFSI V6 the performance option (the B8 Audi S4 3.0 TFSI positioned closer to the E90 BMW 335i than the BMW M3). The Audi A6 (C7) no longer has a V8 engine upgrade in the non "S" range, with the discontinuation of the C6 Audi A6 4.2 FSI that was offered from 2004--2011, one must go to the C7 Audi S6 4.0 TFSI . </P> <P> Audi "S" models should not be confused with the Audi "A, Q, TT" series, equipped with a package "S line" models, which feature leather trim, S - line badging, sports steering wheel and sports suspension, but they are not equipped with a high - power engine . </P> <P> Audi Sport GmbH (formerly quattro GmbH), AUDI AGs high performance private subsidiary, creates even higher performance versions, known by their "RS" badging . The "RS" initials are taken from the German: RennSport--literally translated as "racing sport". The characteristics and cost of these cars are equated to cars belonging to the supercar class . </P>

What the difference between audi a and s
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