Just don't let anyone talk you out of it becuase of "backpressure" I don't know of anyone that has done this mod, and I am looking to do it myself. I believe the guy that threw on the new supercharger that stillen did not put out (can't freaking remember the name) and gained I think it was 19 HP... so I really want to see what someone else can do with it... I am going to do it myself, so Good luck with yours... I am going to go manual at first then if it does work I will go to electric.
Assuming........2&1/2 pipe? If all you are planning to do is add cutouts then match it up with the existing diameter. You will get your flow fix regardless with cutouts. You better post pics and an update if you follow through!!!! HEHEHE
Pi3yeargrad did this on his truck. He's since traded it and bought an Armada, but if you pm him, he may be able to relate his experience with the cutout. From what I recall, it was unbelieveably loud and raucous, which is pretty much what it's good for. It adds a bit of HP & grunt since the exhaust isn't baffled by the exhaust, but if you leave it open on the street, you will certainly attract some VERY unwanted attention..... and possibly a ticket.