locating an O2 sensor in a side pipe

[twobjshelbys]

Mine was on the passenger side about a foot downstream from where the 4 header tubes join the muffler. It was almost horizontal. It's not an ideal position but there isn't anyplace better. This way you get the blending of 4 cylinders. At least there is was mostly out of the way.

Others have put it in one of header tubes but you're only sampling one cylinder...