To my understanding the S/R had the same engine (with addition of the blue valve cover). It has a different ECU, intake and exhaust. The ZX2 and focus engines had different heads, cams and the ZX2 has VCT. I think the block and pistons are the same.
Current Vehicles: 2015 Volkswagen Golf Sportwagen S MTX, 2007 Mazda 3 Grand Touring Sedan MTX
Retired Vehicles: 2003 Ford Focus ZX5 MTX, 1996 Ford Probe GT