It needs to be 18" or more from the port so the sensor doesn't get cremated and at least that far from the open end of the exhaust system so that any reversion doesn't draw outside air past it causing a false reading. It should function properly anywhere between those 2 points.

Make sure you mount it between 10 and 2 o'clock so any condensation can run out of the sensor.

If you mount it downstream from the header it is critical for the system to be air tight upstream to insure accurate readings. Any header or collector gasket leaks can suck outside air that will give you a false lean reading.


Kevin