The Porsche Cayman GT4 hasn't even hit the streets yet, and we already have an extensive review done by Chris Harris. The GT4 is an extreme version of the Porsche Cayman that borrows quite a few performance parts from the 911 Carrera S. These include the 3.8-litre flat-six engine that puts out 385 hp. Chris is testing the Porsche Cayman GT4 both on public roads and on the race track.