Listen carefully to the exhaust note.
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.