I have a custom 3" setup on my duster which exits with 2 1/2 tailpipes and factory tips,i also have dump pipes right after the collectors,testing i've found the car runs no faster with the caps open just a lot LOUDER....
The reason I was thinking 2 1/2" is also so I can use factory tips. Would there be an advantage to a 3" system when its restricted to 2 1/2" at the end? Kev