I did equal length headers modified for an EWG some time ago and i relocated the front O2 behind the turbo, in the downpipe, because it made for better mounting since the 4-2-1 header had very little room in the area with all 4 cylinder merged.

Anywho... I just wondered if anyone had tuned a car with the O2 sensor relocated like that.

Is there any hidden information in the ECU related to the time delay for the O2 response?

My main issue is that the car seems to hunt more at idle than it did with the stock manifolds and also that at very light throttle positions, like going down a hill or something, the fueling will hunt really bad.. swinging from +25 short term to -25 back and forth.

I was considering modifying the O2 sensor calibration to basically deaden the area around 14.7 afr so that perhaps the ecu won't respond as much to changes. It seems almost like the ecu is making a correction and it isn't responding fast enough so it keeps pushing and overshoots.

Any suggestions?

What do you mean you relocated it to the turbo?

Do you really mean you tapped the housing? Or do you mean you relocated it to the downpipe like on the EVO or JDM twinscroll Subarus.

I asked my friend how his twinscroll was working out. He said his car idles just fine. Smoother in fact due to the equal length.

At idle, the flow should be steady state so it should still work fine. It sounds like your front O2 sensor is borked.

Here's a picture of the JDM front O2 sensor position.

http://i141.photobucket.com/albums/r69/mickeyd2005/untitled1.gif

It is in the downpipe right behind the turbo.