What's the most I can safely get out of my stock ecu without flashing it or adding a s-afc? Is it possible to make over 300 whp with it?

 

no...and wouldnt want to anyways...fuel management is the way to make power with these cars anyhow.

 

you could probably get 260 - 270 with no fuel management (turboback, intake, MBC @18.5 - 19PSI)

 

There's only so far bolt-on's will take you without ECU tuning.. And its silly not to take advantage of the tuning when there's "Free power" to be had without any major changes. Ok, not free, but fairly inexpensive..