I have the Nismo header and exhaust. Should I replace the stock pipe that was left between the two with a 2.5" mandrel pipe? The header has a cat so could I delete the secondary cat? If so, what do I do with the 2nd 02 sensor? Will the exhaust be much louder without the cat? Sorry for all the questions. Your help is appreciated.
Nismo Header question
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Well Yes you can eliminate the second Cat and use a down pipe, which will free up a little more power by further unrestricting exhaust flow. Alot of people are running the hotshot header/HP autoworks downpipe Combo. They have been pleased with the results. http://www.hpautoworks.com/hpauhpsedoni.htmlfamilyman said:
As far as eliminating the second Cat, Depending on if you buy a downpipe with the 02 sensor bung welded in already i.e., see link above, all you have to do is IMO, is get a Ghetto Sim ($10) http://forums.thevboard.com/viewtopic.php?t=43023, a great lil thing that screws in the downpipe weld, after which you would then put place your 02 sensor in, and it causes the sensor to read slightly cleaner air than the first sensor, therefore not throwing a CEL. However if you live in an Emissions state, running without a Cat is illegal and you will have problems when testing comes around.
Pretty much any kind of modification that consists of unrestricting the airflow from the engine increases the sound of the car. So yes w/o the Cat the car will be louderfamilyman said:
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It will be loud as balls. You can get 2.25 or 2.5. If your exhaust is 2.5, I highly reccomend a 2.5 inch downpipe. You dont need another cat if you dont mind it being a good bit louder, you will probably be emissions legal though which is a plus. IIRC the 04+ only has one O2 sensor. If I am wrong, as said above you will need a sim to avoid a CEL.familyman said:
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