These cars are so touchy, pretty much anything aftermarket you install, has to be tuned. Like I said, get the AP, and get OTS maps for it. I STILL got a protune, but if you really wanna save some cash (and run a risk over time) just get the AP. Newer gen subaru's are too damn touchy not too. I remember on my bugeye when I had a catless blitz nur spec tbe. A tune was not needed. The car ran pig rich, which was fine. Albeit I wasn't getting the most potential out of the exhaust without the tune, I could still run it without issue. These days, you just can't.