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I am thinking of putting a clifford performance header in. Can anyone tell me what "smog" means. I am from canada and have never heard this term. Do I need a header with or without "smog"
Has anyone ever put a dual outlet cliford on their XJ before. I have a 95' auto

I believe they are refering to the fitting for the O2 sensor.

They are reffering to the o2 sensor along with a warm air pipe for the air cleaner box. But in canada do you have to smog check your vehicle if not then you do not need the smog type just look at the stock unit and see what is attached to it and go from there.

Not related to your vehicle, but to answer your question:
smog is a type of air pollution which is a thick smoke like fog
smoke+fog=smog