For those running a GM Controller for LS setup

[CarlC]

For WB tuning only. On some long-tube applications where the O2 sensor is far downstream in the collector the sensor is not as hot as it is in OE applications. In OE manifolds the O2 is very close to the head, so the sensor gets hotter, and it is less susceptible to being polluted from colder reversion gasses, H and X-pipe effects, etc. In most cases it's not necessary, but the better the sensor placement, the better the tune.