OK I dont know much about cat converters... I have a cat-back exhaust on the way and header also, and I was told to get a high flow cat. there are 2 that im looking at on ebay but im confused on which one will work for me...
-one says fits 01-04 civics 2/4 door and comes with gaskets and o2 sensor hole for $77
-the other says fits 01-03 civic 2/4 door EX ONLY! and only comes with the gaskets and costs $89

i have a 2002 Civic EX ... will these both work and anyone have any ideas on why the difference in prices?
(the pictures look exactly the same)

the 77 dollar one http://cgi.ebay.com/ebaymotors/ws/eB...sPageName=WDVW
the 89 dollar one http://cgi.ebay.com/ebaymotors/ws/eB...sPageName=WDVW

 

unless your pushing alot of horsepower a hi-flow cat is worthless (even with big HP numbers its a few ponies at best). The most you will get out of it is a louder exhaust tone. My opinion... save your money man, put it towards something else.