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Old 07-11-2019, 09:48 AM   #1
IansPlatinum
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Default Minimum wideband distance from O2 sensor?

Not finding my answer here or on other forums.

Just got my 240 back from the exhaust shop, asked them to add a bung for a wideband, and relocate stock o2 sensor as it was in the wrong position and angle.

Now both bungs are about a foot upstream from the cat, but the wideband and stock o2 sensor bungs are only about 4-5" apart. Is there some minimum separation distance required? I'd imagine if they're too close, the one further upstream will mess with the gas flow to the one down stream. Are they sensitive to that kind of stuff?
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Old 07-11-2019, 09:51 AM   #2
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No. There can be an issue with them possibly getting too hot if they are too close to the turbo outlet. But the two of them won't interfere with each other.
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Old 07-11-2019, 09:59 AM   #3
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Here's a visualization of my concern. The cylinder in this example is the probe protruding into the exhaust pipe. Another probe too close downstream might see some weird stuff.

Either that, or just classic Ian overthinking it.
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Old 07-11-2019, 10:03 AM   #4
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You are overthinking it.

I don't think the flow velocity alters the sensor reading in any appreciable manner. If it did, they'd read differently at idle vs. WOT. Or different if you replaced a 2" DP with a 3" DP.
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Old 07-11-2019, 10:09 AM   #5
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Quote:
Originally Posted by JohnMc View Post
You are overthinking it.

I don't think the flow velocity alters the sensor reading in any appreciable manner. If it did, they'd read differently at idle vs. WOT. Or different if you replaced a 2" DP with a 3" DP.
I'm probably overthinking it.

BUT in this example the velocity wouldn't alter the reading of the first sensor, because the density of the mixture going in is uniform. But the sensor behind it might experience a low pressure situation, kind of like your car behind a 18-wheeler on the highway. The reduced pressure makes it seems as if there's *less* air, so the sensor in the rear position might read less O2 than there actually is, because of the low pressure vortex.

But yeah I'm probably just overthinking it. It's my job, OK?
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Old 07-11-2019, 10:14 AM   #6
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It's reading the O2 concentration, which doesn't change based on the velocity.

Like I said, velocity doesn't change the reading, if you take tiny samples of air and analyze them in clear air or buffeting around behind a semi, they're both going to test the same.
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Old 07-11-2019, 10:27 AM   #7
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Quote:
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It's reading the O2 concentration, which doesn't change based on the velocity.
I thought they measured relative amount of oxygen compared to outside gas.

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If you take tiny samples of air and analyze them in clear air or buffeting around behind a semi, they're both going to test the same.
Sure, for concentration, but overall amount is less, just like it's harder top breathe in a mountain range because the air is less dense. Replace the human in this analogy with the O2 sensor. The O2 sensor will say there's less O2 in the mountains compared to sea level, even though the O2 concentration is the same. Or at least I think.



Not arguing, just thinking out loud...
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Old 07-11-2019, 10:33 AM   #8
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The velocity changes a HUGE amount between idle where the exhaust is just slowly shuffling its way out the tailpipe, and WOT/full boost where the air is FLYING by. This is a far larger effect on velocity going past the sensor than is a little turbulence from an upstream sensor. Especially 4 - 5 inches away. And it's not like there is laminar airflow in an exhaust pipe anyhow. Or even steady velocity between huge BANGs from each exhaust pulse followed by nothingness until the next BANG.

And still, the O2 sensor reading at stochiometric is the same at idle as it is at WOT. The velocity doesn't affect the sensor. There is no correction factor for exhaust velocity for an O2 sensor.
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Old 07-11-2019, 10:38 AM   #9
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Once I get a proper down pipe, I'd like to move mine down stream a bit.


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Old 07-11-2019, 10:53 AM   #10
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wow
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Old 07-11-2019, 02:08 PM   #11
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I have used similar distance on all turbo builds I've done with zero issues. Street, track, standing mile... It's not far on a stock redblock turbo either.





First one has LH2.4 stock sensor and a wideband. Sensor in the second picture has even had a coolant flush two or three times at WOT. Places have been properly hot at that point. Still works like nothing would've happened.

No experience on positioning the sensors behind each other. I'd install them side by side anyways but I don't think having them in line is a problem.
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Old 07-11-2019, 04:57 PM   #12
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Quote:
Originally Posted by JohnMc View Post
The velocity changes a HUGE amount between idle where the exhaust is just slowly shuffling its way out the tailpipe, and WOT/full boost where the air is FLYING by. This is a far larger effect on velocity going past the sensor than is a little turbulence from an upstream sensor. Especially 4 - 5 inches away. And it's not like there is laminar airflow in an exhaust pipe anyhow. Or even steady velocity between huge BANGs from each exhaust pulse followed by nothingness until the next BANG.

And still, the O2 sensor reading at stochiometric is the same at idle as it is at WOT. The velocity doesn't affect the sensor. There is no correction factor for exhaust velocity for an O2 sensor.
this.
I don't think the airflow looks like a wind tunnel before the sensors
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Old 07-13-2019, 09:54 AM   #13
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I have nothing scientific to add to this, but when I installed my AEM wideband, it said nothing about being too close to the other o2 sensors. Only that it was recommended to be at least 36" from the turbo. Being to close is said to cause premature sensor failure.

Mines right before the cat at the end of the dp
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Old 07-13-2019, 12:24 PM   #14
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My WBO of my dynomule with WBO B230F + 16T after long sessions might turn to unoperative mode. Sometimes we run several minutes on high load and speed. Quite rare for street driven car. First it was about 20 cm from turbo outlet and I thought it was the reason. So WB was moved to 50 cm further.
Seems work more reliable now. Innovative LC1, so pretty old stuff.

Last edited by OttoB; 07-13-2019 at 12:37 PM.. Reason: Z-esus enklis
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