a follow to my post, post #54
okies.....confirmed....the SMALL PORT STi V7 heads are the same casting as the USDM WRX heads. The BIG PORT casting seems to have started out with the Ver5 STi/RA. They are all the NEWER head casting, which is why they run a different cam than the Ver 1-4. You can see this clearly when you take out the cam and the end caps to where the cam seal is.
Seems all the old school heads are of a large size because it was still OBD1 for the most part and less emmissions then. The NEWER castings, which we got for our USDM '02 WRX and other countries UK? AUS? got the economy heads; small port casting. The S201-S204 heads and SPEC C heads all may just be the same size in port aside from factory porting at the entry, which I've seen in some pictures. Because NEWER cars are coming out, many speculate them to have LARGER ports EVER! But a lot has to do with the AVCS and cam profile which is why it does flow better than the older ones, IMO.