NA Header
 

The lower location has its ups and downs, just as is the case with a higher location. It ensures a broader sample of gasses by placing the sensor after the collector so that the exhaust from all cylinders will pass the sensor. With some more delicate sensors such as aftermarket wideband sensors the added distance is needed to prevent damage from excessive heat. In some exhausts the lower sensor location may put a non heated O2 sensor in a position where it is operating below the desired operating temperature resulting in an inaccurate reading. In this case installing a heated sensor (such as is used in the 7M-GTE) will resolve the issue. I don't know if anyone's had trouble with the added distance causing issues... I don't think it'll be a problem.

The graph below shows (somewhat) that as the temperature increases the range seen as stoichiometric gets smaller. But, get too hot or too cold or too erratic and the ECU will not receive what it views as a valid signal and an error code will be stored.

Attachment 2844

I was planning on putting exaust wrap up top by the block on it. Do you think that will help to keep the sensor hotter down the pipe? Also what do you think a realistic gain is with the header?

Insulation is a good idea, but unless you live in a very dry area I'd get it ceramic coated instead of wrapping it. The pacesetter is mild steel and from what I've read and seen it doesn't hold up to the condensation which collects in the wrap.

I really don't think you need to worry about the exhaust being too cool. Given how much faster the gasses are going to be moving the temp will probably not vary much and N/A exhaust is pretty hot as it is (hence the unheated sensor). If you want to really dig in you could install a portable EGT in the bung and go for a drive. Optimum temp is around 400*C.