I am supposed to be getting my b18c swap installed this week and would like to know what cat converter will work with the swap to connect the header and exhaust? Do I keep the civic cat, or will I have to use the GSR cat? Now also for future reference I would like to know if I install the JDM 4-1 header with 2.5" collector, will I have to get a new exhaust that has a 2.5" piping? Or is there just a way to connect the header with a 2.5" cat and have the cat connect to the 2.25" exhaust somehow. And if I did that, would that defeat the whole purpose of using the JDM 4-1 because my exhaust piping is too small to take advantage? Thanks.

 

what civic is it going into (year/body style)

 

93 Civic Si

 

That's a lot of questions...

1) Neither cat will bolt right up since the lengths would be wrong. Also, the JDM headers with the 2.5" collectors (JDM ITR Headers) are a different length than a GSR header would be. If you were going to modify a stock cat, I would use an Integra one since it should be larger internally.

2) I currently run a DC JDM ITR Header in a 92cx w/ a B18C1 using a Thermal R&D exhaust.... (wow, that's a lot of abbreviations)... So yes... it is possible. The best thing to do is get a cat with 2.5" piping. Get it flared to fit the 2.5" collector and flanged to bolt up to your exhaust. It IS less than ideal. I'm not sure whether it's better than a standard collector header or not... I didn't have a header with my swap so I just bought this one.

-- As I mentioned though... if you're going to get the JDM header, it's probably better to go ahead and do it... that way you won't have to re-modify your piping when you install it.