I wanted to know what the diameter of the entire piping is if i am planning to put a true dual setup with gt take offs, 2.25? also what inlet/outlet position do i need to purchase my mufflers? thanks.

 

Offset/ Offset I learned this the hard way I ordered some C/C flowmasters then had to send them back. only had to pay shipping but still. O/O is what you need and I'd go with 2.25 piping unless you plan to mod your car up then go with 2.5inch thats what I'm doing and its not too big for a pure stock but i plan to rebuild my engine

 

GT take offs, 2.25, aftermarket systems (way better in sound and quality) 2.5.