O2 Sensor (Bung) Placement

Waterbury

True Classic
Finally got the new engine mounted into the car and beginning the process of putting everything else back in place.

I got this exhaust about a year ago and it didn't come with an O2 bung, I ran it as is but I would like to do it right this time. My issue is where to put it as the 4 pipes don't collect until pretty far down. Couple searches on the interwebs tell me 4" down from exhaust manifold is correct, but that would be impossible for me. Will welding a bung a couple inches after my collector cause an issue? Will attach some pics for reference. Exhaust is all one piece welded together. Thanks.
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That looks like a nice exhaust system. Be sure to support the weight of it when it's mounted to avoid cracking the pipes.

As for the O2 sensor location. If you are running the stock FI system and the O2 sensor is the stock narrow band type, then it really isn't that important where it's mounted in reality. They really do not have a lot of function other than idle emissions. These are a old design of FI/exhaust gas feedback loop that do very little compared to the newer designs. Some car manufacturers mounted the sensor in one of the cylinder's runners of the manifold, not worrying about trying to read all cylinders (the assumption being the induction system is pretty much equal for all cylinders and the O2 function isn't that influential so reading just one cylinder is enough). Other manufacturers mounted it way down stream, like at the collector on your header. Those are usually the heated type of sensor so it does not need to be close to the head to fully work on cold start ups (that's the reason for mounting it close to the head on non heated sensors). But even a non heated sensor will work that far down the system once the engine begins to warm up - again it is an emissions thing during cold start ups. But any smog testing that you might have to do is performed when everything is at full operating temp so it won't affect the readings regardless where the sensor is mounted. Basically it's your choice where to mount it. Technically having it close to the head (as your online research found) is correct, but not mandatory. Many of the aftermarket tube type headers like yours have it at the collector.
 
That looks like the IAP header. You can still get new versions of this header from our vendors. I have two of them and here is a picture of one where you can see the bung is past the collector. Must be a good spot! :)
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Awesome, thanks guys! I'll put it similar to Jim's setup. I am running stock FI with stock sensor.

Exhaust was an eBay find, was previously used for "racing applications". All I know is it's got a nice low rumble and sounds nice. Not sure on brand, but does sure look similar to IAP.
 
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