I asked Michael South for his expert opinion and he had this to say:

Hi,
The 02-05 is the same base engine, built for export market from FHI, it uses the 02 STI JDM spec full forged pistons, which have a wide flat plane across the crown above the pin hole. All STI blocks made after and including 01 are semi close deck, including JDM spec which has the hyper crap pressure cast pistons as of MY03. No 2.0lts AU spec STI has these hyper crap pressure cast pistons.

The hyper pistons have a round crown fully turned, no milled tops apart from valve relief’s.

I have had 02 -05 engines apart, not much has changed, although there are different part numbers for the blocks, you need to have 2 side by side to see any difference.

The big issue comes from the hyper pistons in that they are pressure cast, this has seem to be lost in translation where they think the 2.5sti has forged, which they are not, but the piston in the 2.0lt AU spec STI are a true forged pistons.
Cheers

Michael



MSR Rally Team

http://www.users.bigpond.net.au/msgofast/index.html