Today’s 10K Friday is something a bit unique; instead of a normal comparison between similarly valued cars, I’m going to chart the development of the venerable Audi inline-5. While, due to a dearth of examples, we won’t go back to the very early days of the I5 in the U.S., I’ve rounded up some of the more notable configurations that the engine appeared in the U.S.. Since, save some exceptions like the legendary Quattro and RS2, nearly every used Audi with this motor fits the under $10,000 limit (or comes close to it), that gives us the opportunity to see Audi’s continual technical changes to the inline-5. Though not as memorable as BMW’s inline-6 or Porsche’s flat-6, this motor was extremely important to the company nonetheless and was a character-defining attribute of Audis for nearly 20 years. So, let’s see how they kept it relevant from the 1970s into the 1990s: