If you are going to be running any other turbo from stock you are going to need to upgrade the fuel system (injectors, pump) also the turbo inlet. With an upgraded turbo your stock intercooler would also need to be upgraded. Just go back to stock.

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Quote Originally Posted by v6mx6ls36 View Post
If there was an actual Sti intercooler in there then yea , u can get an Sti turbo , if not then the stock turbo it is
To swap a STI intercooler in the GR bodied WRX's you need to replace the entire intake manifold with the STI intake manifold, I doubt the previous owner did that.