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Hello everyone, I am new to this site and I was hoping I could get some answers for some questions about replacing the factory exhaust manifold. I have a 2001 civic LX. Does anyone out there make a good replacement header with both O2 sensor holes that will match up to the OEM exhaust? I see the headers out there with the two holes for the O2 sensors that looks like it would work. Can anyone tell me why they put the top O2 sensor hole on the right side of the header ? will the factory sensor wire be long enough ? Next question, how will the O2 sensors behave without a convertor anymore. One last question, has anyone gutted out the convertor and reinstalled it? If anyone knows of headers that are nice please let me know, the only ones I have checked out are the ones on ebay with different coatings on the tubes and I am not sure what is the best coatings to get. thank you everyone.

 
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Without a proper/properly working cat, your car will throw a p0420 code.

 
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Agree without a cat you have to modify the O2 sensor to avoid CEL

 
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is modifying the 02 sensor possible to do and do both of the them or just the top or bottom 02 , thank you

 
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I was talking about secondary O2 sensor only. You can't modify the primary. There was a diagram few months ago in the forum regarding fixing P0420 (bad cat) code.

 
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A little late to the game, sorry.

Just use an mechanical "extension" (sometimes called a CEL eliminator, O2 Spacer, etc.), on your secondary sensor. I use them with my hi-flow cat on the street and on my "off-road use only" header (without a cat) on the track. No Codes, ever. Just make sure your sensors are both in good working order. Good luck.

 
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yeah buy a Megan cell eliminator like this one with a bend so theres more room for the wires http://www.ebay.com/itm/Megan-Racing-Mechanical-O2-Fix-Version-2-/361386689295?hash=item542453430f

 
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thank you everyone who has replied, my next question is , which header is the best one to buy for fit and finish also for attaching my oem exhaust pipe, thank you again

 
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Not a lot of choices for when it comes to D17 headers. Megan, OBX, eBay are the typical economy routes. You can get custom headers (or the knock-off) from Bisimoto, PLM, KTeller, etc. Or the tried and true, DC Sports 4-1 (HHC5019) or 4-2-1 (HHR5019). I have both.

 
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The best I believe is the magnaflow manifold catalytic converter and is literally the same price as oem heard a lot of good things about it though. Hope this help.

 
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The popular one back in the day was the kamikaze header. Still rocking one (ceramic coated) to this day

 
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ive been using Megan for last 6 years the only issues are the supplied bolts are rusted to **** and most likely seized and the subpar gaskit that came with it other then that no problems. if i could go back i would have spent the extra money on a DC ceramic coated header.

 
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Most headers come with both bung holes, check before purchasing.

You may not need the emulator (spacer) for the downstream o2, every car/header/ECU is different. I say install a header with both sensors and get a emulator only if it pops a code.

Don't throw parts at, it unless they are needed.

If you want it Cali smog legal, then Magnaflow offers a high flow manifold/cat for about $500 (OEM is about $450).

 
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Bad News - Technically, the only legal cats in California are OEM or OEM equivalent.

Good News - Nowadays, 2000 and newer vehicles only have to pass a visual inspection for the cat, but if it doesn't look stock, it won't pass (unless the tech is clueless or just doesn't care). Even if you do pass a visual, the sound/smell would set off alarms. You'd only pass a smog, only if the high-flow was freshly installed (maybe). They get worse after some time. High-flow cats degrade pretty fairly quickly/significantly. There's barely enough material to effectively convert/burn-off gas when they're new. They deteriorate at a much faster rate than stock. I've been running a Random Tech Hi-Flow for about four years. Nowadays, it's pretty much just a straight pipe. I always swap back to stock for my smog checks.

 
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The $500 Magnaflow high flow manifold is the only Cali legal high flow option that I have found. I had a magna flow in my other car for a long time without problems, until I ruined it by driving a long distance with a misfire.

 
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Or C.A.R.B. approved.


"49 state" cats are not approved for California.

 
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The carb number also has to match for your vehicle, so don't try to get a carb cat off a chevy.

 
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there was only one time i had an issue being catless when my usual place had a new guy that did everything by the book and crawled under the car i just played dumb when he told me there was no cat and i wouldn't pass. he ran the test and lo and behold i passed which he wasn't happy with but he let it slide.

 
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Wow You pass catles?
What are you driving? Wolksvagen?