WBo2 Sensor location and depth

I have a couple rules of thumb i follow for o2 sensor location, but wanted to get some feedback from others- what is your rule of thumb, distance from exh. valve/distance from head/in a straight or in a bend.... and any others, Lets hear some experiences! I have done some testing on large displacement engines with big cams/large overlap. distance from end of a large open collector that is very short is critical- sometimes have to put the sensors in the primaries to get decent readings even at WOT

Second question is how deep does the sensor need to be into the tube? in other words some bungs are shorter than others, how much of the sensor tip needs to be into the exhaust flow?

In a typical installation with a road car I normally fit the sensor to the collector (N/A engine) or about 500 mm post turbo in a turbo engine. These aren't set in stone though and often you're limited by where you can physically fit the sensor in a tight engine bay. If you're running a race exhaust then distance from the open end is probably more critical than anything as contamination with ambient air can be a problem. I'd generally like to see the sensor at least 500mm from the end of the exhaust but again sometimes this may not be feasible.

Most weld bosses will have the tip of the sensor protrude into the exhaust around 10 mm and this works ok in the exhaust. If you're mounting the sensor in a primary runner then I'd use a longer boss to move the head of the sensor back out to be flush with the runner wall. This is how the bosses for the AEM 4 channel UEGO work. The sensor still reads just fine but it means the sensor isn't exposed to as much heat and it doesn't interrupt flow as much.