lets say i bought a greddy evo catback an a car then for some reason or another i go to the muffler shop and have then bend me the same diameter piping and swap the greddy piping with their piping, will the sound change? because i bought my friends muffler frm him a long time ago and did a 2.1/4 piping and it toally sounded different, both have same cars. thanks

 

greddy has the packaging inside the muffler, so i think the sound will be different

 

You're asking if two pipes of identical size & shape will somehow magically sound different? I think you answered your own question.

Any difference in sound will be attributed to a difference in the resonator or muffler setup.