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Headers, smog compliance and street legality

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  • Headers, smog compliance and street legality

    I live in Nevada. How might headers effect my ability to be smog compliant and are they legal for normal road use?

    I would like a touch more​ performance, but not at the cost of complications with the law.

  • #2
    as long as you still throw o2 sensors in it wont be noticed when you get your emissions tested.
    98 EO SVT Deleted Cat/Blue Chip in PCM/Foglight Mod/Moosing Fix BAT struts/spring Carbon Fiber Cowl Hood & Carbon Fiber Nascar Trunklid

    2000 Red/Tan SF connectors/ frontnrear strut braces, BAT struts/springs B&M shifter, Bosal Exhaust/ Dynomatted,


    • #3
      Technically headers are for off-road use only. The pre-cats built into the exhaust manifolds are for emissions control on start-up, iirc. The main cat under the car is the main control for emssions.

      To pass emission testing with headers you will need mil-eliminators. The lower O2 sensors could be turned off via tuning but this can be detected by some states during testing and could cause the vehicle to not pass testing.
      - 12 Focus SE
      - 99 Contour SeVT <- 3L/NPG Turbo
      - 2k Contour SVT - #2137


      • #4
        Some states do a visual check (usually with a mirror) for elimination of emission equipment, including pre cats. The pre-cats function primarily as the main source of emission cleanup, where the downstream cat is a secondary cleanup source, since the precats are monitored. Technically you can remove the secondary cat and still pass emissions on this vintage of car. I had a customer with an 03 Elantra with a gutted secondary cat and it passed the smog check due to the precat doing the work. Emissions was a bit higher, but within allowable limits of the state/federal government standards. On some cars, particularly newer cars, the precat and secondary cat are monitored with separate o2 sensors. My 09 Mazda 3, which was CA compliant as required by WA state had 3 separate o2 sensors, one in the manifold, one behind the precat and one after the secondary cat.


        • #5
          Some people might be able to cheat the emission system with headers if they relocate the downstream o2 sensor to be after the secondary cat. On a V6, that would be extremely difficult to accomplish because both sides need the o2 sensor readings to reflect what the primary o2 sensor is doing. The ECU doesn't like each side to be identical.