O2 sensor extension

There are two on each side. One in front of the converters to determine oxygen content and one behind the converter. If you have the four into one header you need to place the front oxygen sensor as far back as possible to avoid exhaust pulses. So as close to the front of the converter as practical. The one at the back of the converter will be in the same location if you are just reusing your old converters. If not measure what you have now and leave the distance the same.