OBX, ughhhhhhhhh! There's a reason you got it for free, think about it.
Honestly, save up for a better cat bro. Like I previously stated a "Carsound" cat would have been a better choice for your teg. I highly doubt you would have got a check engine light with a better cat selection. You get what you pay for.
There's some better quality high flow converters on this website.
http://www.car-sound.com/universal/935.htm