Audi's S-line vehicles achieve a blend of performance and luxury by starting with their already classy and well-appointed sedan and packing in a winning combination of a high-output engine, nimble suspension, and powerful braking. Their entry-level offering into this high performance category is the S4, built on the A4. Like the A4, it is offered as a sedan, wagon, or convertible (depending on the year) and includes all the premium options available at the time. Though what make it different are all the sporty and track-inspired Audi S4 parts. Many different engines were available over the course of its evolution, starting with a turbocharged 5-cylinder engine, then changing to a turbocharged V6, switching to a naturally aspirated V8, and then offering a supercharged V6. The Audi S4 is sure to inspire and never disappoint. Fun fact: to celebrate 25 years of Quattro technology, Audi released a Audi S4 25quattro in the US in 2005 - only 250 units were made.