Between `1997` and `2001`, the `S4 B5` is much more than a quick `A4`. Against a BMW 3 Series, it already pushes the idea of the very fast, discreet `quattro` saloon with big tuning potential and real sleeper charm. Today it is a fascinating car, but rarely a cheap one once you bring the mechanical side back to proper standard.
At the centre sits the `2.7 V6 biturbo`, in `AGB` or `AZB` form, usually with a `6-speed` manual and in some markets with `tiptronic`. The engine can be superb, but it demands discipline around oil service, warm-up, cooling, small hoses, vacuum lines, sensors and the condition of the `K03` turbos. At this age, you also have to read modifications properly: a heavily altered or badly returned-to-stock `S4` gets expensive quickly.