This has probley been covered a million times but need a quick answer.

Want to go full decat and looking at downpipes. My car came with a cat back exhaust (middle pipe and backbox) would a decat down pipe with a 3 inch exit mate to the system ive got or would i need a 2.5? Most i see are 3 inch so not sure.
Thanks!

 

You can get 3inch that tapers down to 2.5inch to join a 2.5inch system.

 

Sorry what i was trying to ask is can you bolt a 3 inch outlet downpipe to the flange on a 2.5 inch centre pipe without isues?

 

Its best to get the correct 2.5" downpipe for a better fit but with the correct gaskets and a bit of exhaust putty yes its possible to get them to seal.

 

http://imageshack.com/a/img633/9485/ZGiPW6.jpg

In you opinion do you think ive already got a 3 inch cat back? Ive looked and the middle pipe looks more beefy! Thanks

 

Hard to tell mate, the centre pipe usually has a resonator fitted which makes it appear more "beefy". Most people generally keep to the same size bore throughout rather than mix and match and have bottle necks in the system.