If I decide to swap out my fuel rail with an AEM fuel rail (different bore I am guessing), will the car need to be retuned? I'm having it retuned anyway but I'd prefer to do it myself to save money if it's not going to be a problem to install

 

From what I've read, yes you will need a retune. A WRX message board says that your AFR will become richer because of the aftermarket fuel rail.