im looking at an obx high flow cat off ebay,
- will it make my car louder?
- will it decrease my torque?
- HP gain?
- is it a piece of shit - or worth the money, and can i use it with all stock piping, i have stock header, and stock piping to my muffler.

IMO everything OBX is garbage. Go with a carsound cat. They will make your car a little louder since they are free-er flowing, and should increase hp a little bit, nothing substantial. And every aftermarket cat i've seen is weld on because they are universal applications. You can have a flange made and welded on so that it will bolt up to your stock header and exhaust piping though.

the cat is for a 92 - 00 honda civic - i have a 96 civic

you wanna give me the link?

yeah - i think this is the link :
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&category=33629&item=2466198175&sspagename=STRK%3AMEBWA%3AIT

if this doesn't work - just go to ebay motors, and look up OBX high flow cat, and look at the ones for 92-00 civic

oh it has flanges already. That should work with your 96 then. It'll bolt right up.

do you think that it is worth it? will i sacrifice torque?

it's completely up to you, I don't know how good these things are, OBX tends to be a little shy in the quality department. You will see a bit of an HP increase and maybe a little torque decrease, but nothing huge.

From what I have seen, you will probably loose a little in the bottom end.
I also ran into problems with emission testing. If you live in a city you will want to keep the stock 3way cat for when you need to register. I couldnt pass emissions here in Salt Lake City. I figure California would be even worse.