[vettestr]

For my 2 cents I ran into a lot of grief with 02 sensor placement on my toy. I did not want it to be visable so the options were limited. You want it as close to the engine as possible to for more accurate readings. As you get farther away from head you loose heat quickly and this will skew reading I found out the hard way. You also want to install sensor so moisture runs away from it rather than into the sensor from condensate. After getting readings I did not believe I moved mine to the rear most tubes on each side (ran 2 sensors) thinking the rear cyl. would be the hottest so would be most effected by lean settings first.
Wound up with sensor about 18 inches down from the header head flange . This placement changed my readings by (.20) OR leaner than when in sidepipe without and setting change. So just placing closer to the head changed my display from .84 to .64 and that was about where I expected I was at. There was just no way I was running as rich as what it was trlling me when in the sidepipe just after the last 90 degree turn.