They do use 2.5" flanges and they do bump the pipe up right at the flange. The pipe other than the flange area is 2.25" outside diameter. Borla has the smallest pipe for any cat back that is offered after market for the Z32TT. I have measured many of them in front of many customers for many years. I have seen very old ones and very new ones and have never seen a 2.5" pipe Borla system for a Z.