My friend is trying to make me a long 4-1 header. Header is almost ready but i have one question, where should be the O2 sensor? In one pipe or where all 4 joins? How are all the other long headers built like HP racing ???

Thank you

 

I would think you would want it in the collector.....many of the other headers I have seen DON'T have the sensor connection....they are for race applications and they couldn't care less about a check engine light comming on.

 

Put the O2 sensor in the collector about 3-4 inches from the flange where the header connects to the rest of the exhaust.