the german touring car S170 focus had 250bhp (flywheel) with normall aspirated mods (better head etc) but the bottom end was the same as a stock ST170. i looked at a St170 head the other day which my friend has had ported and flowed, its a bit different to a zetec head anyway but you could see beforehand they arent ported/flowed as standard.
svt head will go onto a zetec block but i think the pistons might hit the valves
