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Discussion Starter #1
Just purchased a AT-200. Looking for info on where to drill the header, to install the bung for the O2 sensor.

Thanks in advance.

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Discussion Starter #2
Another member in club700xx sent me this.


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If I had to make that decision on my own I'd mount the sensor further downstream in a straight section of header just upstream about 5-6 inches from where that header dumps into the muffler. Your pipe shape and available space around the header might not allow an optimum sensor location though. As a general guide on a single cylinder motor with a single pipe exhaust you'll want to insert an EGT or O2 sensor nearest to the end of the primary pipe.

Never insert a sensor into a bend if you can help it because the sensor will not be exposed to a uniform flow column. The exhaust gases attain their highest temperature and expansion rate, and maximum stabilization of gases right at the primary pipe exit. This assumes that the primary pipe length and diameter are optimum matches for the motor. :)

So, for example if you insert a sensor upstream midway in the pipe you'll get inaccurate, inconsistent and dirty readings in that underdeveloped column of gases. Its real dirty up there in most throttle positions/torque loads... its still consuming oxygen, still continuing combustion and producing heat and still expanding, so column density/distribution of gas' molecules is decreasing rapidly as the gas' velocity increases... thats a very unstable environment for data gathering.

Grab your data where its most stabilized at its maximum temp if ya can. You can find that sweet spot for data gathering in the primary pipe (single cylinder only, multiple primaries data gathering location is inside the collector) with an EGT sensor.
 

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I would focus firstly on where you can put the sensor bung where it will be easy to install and remove the sensor, rather than what position is optimal for the sensor to function. I'm not saying that is not important but on ATV's in general space is tight and there is usually only a few places they will even fit.

On my Renegade I have 2 bungs welded on the head pipes (2 cylinder, I can tune each separately) they are not where I'd put them as a first choice but they are where they would fit. I think if I had it over I'd just put a single bung further downstreram past the collector and forget about doing a dual cylinder tune but that doesn't really apply here. lol
 

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Discussion Starter #6
Thanks guys for all the info. Only other thing I've read, was 9" from header flange? I wasnt sure what they ment by flange, where it meets the motor or mid pipe?

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Downstream near the end of the header pipe in a straight section is usually the best location. But it might be difficult or impractical to tap into the pipe since its usually quite tight back there, as Mac explained. The ideal location can only be found by probing with an EGT, especially true on stock-type bolt-on pipes that are not optimal performers to begin with.
 
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