Rep Power: 0

So ive decided to mod my 2001 civic ex's intake and exhaust. Starting with short ram intake, throttle body spacer, and axleback exhaust. (I am not replacing the exhaust manifold with headers because there is an o2 sensor on it and i don't want to be running with an engine light on - i still need to pass emissions. Also i don't want my engine to be running too hot since my short ram will be right there) But i have one question remaining...

If i install a 2.25" diameter exhaust system catback, should i get a cat with the same size pipe diameter as my catback, or should the pipe diameter be the same as what would attach to my exhaust manifold's pipe? since these won't be the same size, how should i go about fitting these together?

This is also my first post here, so hello everybody!

 
Rep Power: 518

I assume the car does not have a cat related problem at this time? No P0420 code?

If you have to pass emissions tests, I'd say to leave the factory cat on as long as possible (until it sets a cat code). So leave the cat alone, and go with the cat back exh.

A good stock cat is not restrictive to the stock engine it was designed to be with. It can flow more CFM than the engine can breathe.

An aftermarket cat is almost never as good as a factory cat (quality and efficiency, as far as CEL/P0420 code and emissions tests go).

JMHO. YMMV.
HTH

 
Rep Power: 511

If you have an ex, there shouldn't be an O2 sensor on the exhaust manifold. Both o2 sensors on the D17A2 (01-05 civic ex engine) are located on the downpipe: one where the downpipe makes that 90-ish degree angle, and one right after the cat.

if you buy a catback, it'll still mate up just fine to the OEM downpipe. Also, an aftermarket header will also bolt right up to the inlet of the OEM downpipe. Just some food for though.

 
Rep Power: 0

thanks a lot guys