Hi all, just a little info on the ST170 engine for you. Barely any components are the same as the european engines, except perhaps the crankshaft. The block is slightly different, but is interchangeable with the blacktop one. The rods are a different length to the european ones and are made from sintered steel, the pistons feature valve cutouts and a slight dish and are also a different pin size. The head is also different, it has larger inlet ports, Longer valves and springs, solid followers and is designed for variable camshaft timing on the inlet cam. As a note, all 2.0 zetecs are equipped with under piston cooling jets, the performance 1.8 engines (130bhp) were also fitted with these.
Also as stated, they rarely make the 170bhp that they claim, but are more than capable of that power and more with some tweaking.