I originally was going to put a wideband O2 sensor in my down pipe like the original exhaust housing for the XR4Ti, but then realized I have long tube headers and that would put the sensor far from the ports. There is not a lot of room around my collector or "up pipe" (this is my Europa TCST project), is it ok to put the sensor into the 45 degree adapter flange just before the turbo?
I've always seen and installed the o2 sensor after the turbo. I would put it in your downpipe in the first 90
It seems my memory is short and I asked this in September of last year......will put it in the downpipe
This is not advisable. The oxygen content measurement is sensitive to the pressure of the gas being measured. 99% of commercially available sensors are calibrated to read accurately at 1 atmosphere of pressure. There are sensors and amplifier electronics specifically suited for this, such as the Bosch LSU ADV which has a documented pressure compensation curve for pre-turbo applications.
O2 post turbo, 1 egt per cylinder in exhaust pipe. 
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