More on the SKYACTIV :
MAZDA: VISION | SKYACTIV TECHNOLOGY | Mazda Spirit
I find it really interesting that Mazda decided to increase the compression ratio on the gasoline engine (14:1)
MAZDA: SKYACTIV-G | ENGINE | SKYACTIV TECHNOLOGY
meanwhile decreasing the CR in the diesel version
MAZDA: SKYACTIV-D | ENGINE | SKYACTIV TECHNOLOGY.
Some very interesting information on that website regarding the necessary adaptations required by these engines.