Anyone know the outlet diameter on the OEM cat (at the flange)? I'm guessing 2.25 and hoping for 2.5.

 

No one knows?

 

I am fairly certain that it is 2-1/4 inch, but others will post to verify or not.

If you are thinking of modifying the OEM exhaust (i.e. one ball) I had it done and the muffler shop suggested keeping the size to 2-1/4 to retain the required back pressure. In the end, I doubt if 2-1/2 inch will make any noticeable improvement, unless your motor is putting out 300 HP.