Listen carefully and you'll notice something different about the Porsche Boxster and Cayman caught testing at the Nurburgring. Did you hear that? Neither one has a flat-six. You can tell by the exhaust note. Sources from the Nurburgring believe these are in fact test mules for the upcoming four-cylinder versions of each car. As we've previously reported, Porsche is planning to offer a turbocharged flat-four in many of its upcoming new models, including the Boxster/Cayman duo.

It's a bit hard to tell from this video whether or not this engine is turbocharged or not, but we know both naturally aspirated and turbo fours from Porsche are coming.