Volkswagen-Audi Group
(Porsche were in F1 with their own cars in the early '60s, and they came back as an engine supplier to McLaren between 1983 and 1987, and then pulled out after making a disastrous engine for Footwork-Arrows in 1991, being unceremoniously dumped mid-season. They never returned, but a prototype F1 V10 engine has undergone a lot of modifications and transformations and is now the V10 in the Carrera GT)