Hi, I am not sure but, downpipe and exhaust will help de-cat or down to single sports cat then a remap should see some power gains.
Not sure if you will need to change the turbo.
I have a wrx so the list for that is exhaust, turbo, fuel pump, injectors and remap
So the sti starts out with more power so should just need a few improvements. I know you will get 350+ without to much work but it's getting into the 400's that might be costly.
But I am no expert.... One should be along soon.
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