[bazza]

Stock pistons are fine to a lot of power and cylinder pressures as per any other Subaru engine. Issue is the tune, not many people actually understand this and never will. My current engine in the racecar is a stock STI engine running close to 30 psi... good safe tune!! And the old EG33 saw up to 15-16 psi on the dyno and ran around a racetrack for a long time at 7-10 psi. Given the cost of forged pistons I probably wouldn't touch the stock ones unless aiming for above 500 bhp. The power above is nothing for these pistons.

Get a good safe tune and it will run a lot of boost for a long time. I couldn't break my turbo EG33 at the track in the harshest of conditions (major oil surge and 32-35'C). Get the tune wrong and it will last 5 seconds!!