Silver top head on a blacktop bottom end or other way around is a total ball ache I would not bother . The st 170 head is the best flowing head of all the zetecs and has larger valves as standard so I would use that as st170 blacktops are the same engine with different heads and internal parts. Silver top is the early zetec and are totally different so mix and matching can be done but as stated above a real ball ache.


Cheers paul