I know this has been asked before but what all do i need to delete my 2 1/2 cat and put a pipe running from my y-pipe which is 2 1/4 to my catback which is 3 inchs?

 

You would need a piece to connect the y to the catback obviously. You could use 3"-3"connector to connect a 3" piece of pipe where your cat was and a 3"-2 1/4" converter to connect the 3" pipe to the 2 1/4" y pipe.

You could also use a 2.5 inch pipe where the cat was and use reducers to step it down more gradually to the catback so it would be 2.25 to 2.5 to 3".

You could also find a shop that will drop the cat for you and weld a piece in.