well what are your plans and how loud do u want it?
2.5 will be good and safe from tickets
3in depending on muffler could be safe but will sound wicked!
and 3.5 no if you wanna drive it on the street there is no need for a 3.5
oh and unless you are a d-bag DO NOT GET A TIN CAN
be original , stand out and get a proper muffler so everyone, including myself does not laugh at you
