Porsche has made plans to revive its close ties with Audi, following the sports car maker’s takeover of the Volkswagen Group.Well placed sources say that Porsche bosses are keen to restart the kind of engineering collaboration with Audi that produced the RS2 super-estate in the mid 1990s.One of the first Audis in line for a Porsche makeover, once the company directors give the green light, is said to be the upcoming A5 Sportback, a more practical version of the A5 coupé with two more doors and a bigger boot.