Email from a mate who is currently writing (which is about to go to press) the definitive 'Zetec' book, to be printed by Haynes.


"I have measured the ports on 2-litre Silver Top, Black Top and
ST170 plus re-measured the port sizes and the throats. Plus I know the
combustion chamber volume of these and the port volume of Black Top vs ST
170 - 26-cc in it - ST170 are bigger. Throat size is
different too - plus the valves are 0.5-mm bigger.... I measured the lot
myself by the way - bought a Burrette!

Port size on an 1800 is the same as 2-litre - but that's on a 130 1800
head - the 105/115 is different - different combustion chambers too, and piston -
has a bowl in it...

Interesting the Silver CC is 46 and the Black is 42 but the black has a 4-cc
dish in the piston - bringing it to 46-cc!"

I can get exact measurements at a later date if it helps.