I have a HKS Downpipe and Cat Back Exhaust ordered and was wondering if i need to buy a new high flow cat. I am strap for cash atm, so i want to just use the oem for the time being. However i have looked under the car and it looks like the oem cat is not detachable. The three questions i need answered are. Is the cat detachable. Does the cat-back exhaust provide the cat. And if i need to buy a high flow cat later on what is a good one for my scooby.

Any help is much appreciated
Thanks