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What size header and catalyst to get for 00 si?

Old 08-13-2014, 03:53 PM
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Default What size header and catalyst to get for 00 si?

name:Tim
Location:Richmond
Question: what size size header to get and catalyst
Contact: pm

ok so i have a 2000 civic si with a apexi ws2 catback. i have a fault for the catalyst which needs to be replaced. Also my stock manifold has exhaust leaks so i figured i would fix all of this at one time. I'm having an issue for some reason rapping my head around what size to make this work. the catback is 60mm which is 2.3 inches, and most of the headers are a 2.5 piping to the cat. my question is what exactly would i need for the header to bolt to the cat, and then to the rest of the ws2? any real help would be grateful, and a better understanding would be 100 percent awesome!!
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Old 08-13-2014, 05:48 PM
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Default Re: What size header and catalyst to get for 00 si?

Ideally, by the end of the catalytic converter, you want to be stepped down to 2.25 inch.
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Old 08-14-2014, 03:52 PM
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Default Re: What size header and catalyst to get for 00 si?

Yes. What would I do for the catalyst to be the median between the two? A catalyst would only have once size for both ports. Yes this is a real question haha.
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Old 08-14-2014, 07:07 PM
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Default Re: What size header and catalyst to get for 00 si?

Your local parts store should have a 2.5 to 2.25 reducer, or let an exhaust shop do it. It shouldn't be expensive for something as simple as that.
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Old 08-16-2014, 03:45 AM
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Default Re: What size header and catalyst to get for 00 si?

buy a universal converter for a 00 civic Si because it's required by the EPA and any good exhaust shop can weld the gap.....
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Old 08-16-2014, 10:05 AM
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Default Re: What size header and catalyst to get for 00 si?

If you have exhaust leaks, and are getting catalyst faults, how are you sure that the catalyst is bad instead of just having a front or rear O2 sensor problem?
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Old 08-16-2014, 01:14 PM
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Default Re: What size header and catalyst to get for 00 si?

have the converter been flow tested to make sure it's actually the converter that is bad?
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Old 08-22-2014, 03:27 PM
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Default Re: What size header and catalyst to get for 00 si?

Already replaced the o2 sensor before the cat. Did a cap discharge (not positive if it works on this car) but everything was cleared. Drove the car 800 miles or so from va to PA then back and the car threw the cat fault once I got home. I have not had a flow test done.
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Old 08-22-2014, 04:40 PM
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Default Re: What size header and catalyst to get for 00 si?

The O2 sensor after the cat is what determines cat efficiency, it gets compared to the O2 sensor before the cat. The O2 sensor before the cat is the one the ECU uses to do closed-loop engine control. So you may want to check the rear O2 sensor out.

Last edited by Fabrik8; 08-23-2014 at 12:43 PM.
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Old 08-23-2014, 11:27 AM
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Default Re: What size header and catalyst to get for 00 si?

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