These days, we take it for granted that the Porsche 911 uses a flat-six engine. That's because every version of the iconic rear-engined sports car has had one. Right? Well, for the most part. There was the 912 that joined the original in the late Sixties with a flat-four. And in the mid-Eighties, Porsche toyed around with the idea of a V8-powered 911.