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O2 sensor placement when using headers on an '81

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Old 06-20-2013, 05:22 AM   #1
jotto
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Default O2 sensor placement when using headers on an '81

This might be a dumb question as I think there is only one answer but. ...
On a stock 81, the O2 sensor is quite high up the exhaust near to the manifold. When using headers I assume it has to be relocated to the collector.

Is this correct and if so, what difference if any does it make?
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Old 06-20-2013, 08:29 AM   #2
texas jim
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Or the same distance from the collector on the stock stainless headers that came from the factory. Good question. I'd imagine that the best reading would be where the O2 sensor was placed in the factory. But I imagine one of the more knowledgeable guys on here will let you know. We are blessed to have some real smart cookies on here, and I mean that.
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Old 06-20-2013, 08:39 AM   #3
mrvette
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The O2 sensor needs to be heated, 3 wire, two white wires, one to ground/engine/frame, other to the fuel pump +12 feed wire which is controlled by the FP relay/computer..... the black wire goes to the computer same as what you have now.....

here is the trick, the sensor needs be mounted at least at an angle pointing down at the sensor tip, wires in the air high/up top....

vertical is best, but long as it's not upside down.....has to do with condensate/drainage.....

so to get an O2 sensor bung to weld to the header collector some distance down stream from the actual pipes joints...
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Old 06-20-2013, 09:57 AM   #4
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I welded a bung on the collector and went with a heated O2 sensor. I tapped the heater circuit into the choke wire and the other wire to ground. it's really easy.

no electric fuel pump on a stock '81
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Old 06-20-2013, 11:43 AM   #5
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So any universal heated O2 sensor 3 wire will work?
Had a quick look online and found some starting at $17.50 but would probably go for a Bosch @ $28.
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Old 06-20-2013, 11:59 AM   #6
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We made up some BBC dyno headers and we were asking the same question on where to put the 8 Bosche sensors?

Some where in the paper work was the optimum working heat range. So we fired up the engine with a medium dyno load to get the pipes hot. Then with an IR termal reader gun we measure the pipes temps. We ended up welding on all 8 bungs about 4 inches down the primary pipes.

It seems to me that the pipes were nearly 1150 degrees F. on that motor on the top of the primaries and only 800 degrees 28 inches down where the primary pipe came together near the colector.
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Old 06-20-2013, 12:12 PM   #7
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Quote:
Originally Posted by jotto View Post
So any universal heated O2 sensor 3 wire will work?
Had a quick look online and found some starting at $17.50 but would probably go for a Bosch @ $28.
I think I used the Bosch replacement for a Corvette with a 4 wire sensor. but a 3 wire will work as well.
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