Rep Power: 0

Can anyone please tell me why some of the aftermarket exhaust manifolds for the d17a2 vtec, have a sensor hole in the header? My car is a 2004 civic si 4-door Canadian version equivalent to the ex model elsewhere. I have a magnaflow catback installed, my downpipe rusted out at the flange after my cat so I just ordered a magnaflow cat/downpipe and want to do the header at the same time. The stock down pipe as well as the magnaflow have 2 holes for the 02 sensors so that seems straight forward, just the aftermarket header for some reason have the extra 02 hole

 
Rep Power: 512

Because the D17A1 has an integrated cat/exhaust mani, and the upstream sensor is located shortly after the head. Some of the headers you're looking at are probably designed as a "universal" D17 fit, if you will. Likely those are made just to look shiny as opposed to any performance gains.

 
Rep Power: 518

If your application doesn't need to use a sensor hole in that location, don't use the hole.

 
Rep Power: 147

Sounds like those are D17A1 headers you are looking at. I did my EX header D17A2 with a DC Sports Ceramic Header. No holes for o2 sensor there on a D17A2 EX 2002 model. For pics visit my garage.

 
Rep Power: 147

I absolutely agree. Those are most likely for looks. You can get those for $60 but they are not equal length pipes and the collector is restrictive. I recommend DC Sports Ceramic 4-1 header. It is not cheap but it's good and it will give you more power.

 
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Opinions on the obx header for the d17a2? This header has no bung for a 02 sensor. I live in Canada and to ship a header up here from California I'm being quoted between $65-$75usd for shipping alone. Any Canadian members here know a good place to buy one in Canada?

 
Rep Power: 222

Whereabouts are you in Canada?

 
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Ottawa

 
Rep Power: 222

I know of a good place in Toronto but I have no clue about Ottawa. Any local car groups you can ask where they get their parts? Or any friends that modify cars?

 
Rep Power: 229

It makes more sense to tool to fabricate 1 header form that fits two heads than to create two header types. Better for cost, less people returning item because they bought the wrong one.