i have an 07 2.5i and have an N1 muffler on now and it sounds alright, but i want something louder.... i'm going have a custom cat back put on soon, and was wondering whats the best size piping for sound and performance WITHOUT loosing too much low end power. Also which muffler will sound best? As in loud, deep, with the poppy sound. I should have just bought a WRX, it would have been ten times easier to mod it!!

 

2.25" internal diameter is what you want for non-turbo.