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Wideband Tailpipe Sniffer Tube Design - Input Wanted 
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For a long time I've wanted to build a general purpose tool for measuring the exhaust mixture of any random car that I felt the need to. Well, I just ordered the wideband controller, display, and sensor to do just that. So now I need to design and build the rear end of this arrangement, and thought I'd seek your input, whoever y'all are.

Requirements:

  • Effectively guard against reversion
  • Clamp to the outside of the tube in a non-damaging way
  • Fit relatively small pipes as well as larger ones with equal efficacy

Examples:

Innovate has one that seems extreme, but might be the minimum required:

http://stuff.fredcooke.com/innovate-clamp-highres.jpg

Image



FAST have one that seems insufficient:

http://www.fuelairspark.com/fas/ez-clam ... t-kithtml/
http://www.jegs.com/p/FAST/FAST-EZ-Clam ... 8/10002/-1

Image

Image



My thoughts? Innovate's one puts the sensor in quite a laggy spot. But perhaps that's to guard against water droplets having a direct path to the ceramic element? Optional rubber cap for the screw clamp would be nice. Lower diameter is better than higher, and something bigger will allow a higher air speed through the centre past the sensor. Maybe 25mm or 30mm ID or something like that for optimal sensor-pipe geometry? But if you want to dump it out up stream rather than down stream, 2 times 25mm is getting pretty big. Not much more to say right now.

Any and all input welcome! Post away! :-)

Fred.

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Wed Nov 25, 2015 9:52 am
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QFP80 - Contributor
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I have and use an innovate one still with my AFX (since my LC1 died, thankfully :roll: ).

Seems responsive enough for road tuning only issue is at idle there is often not enough flow, so it can't create enough draw to keep gas flowing through it and give a usable reading. At least on the size tailpipes mine is usually jammed in.

Local dyno one is a straight bit of pipe and I don't really like it. I have a bung welded in downpipe before going to the dyno. Or 2, if I'm feeding into dyno and also into ECU - or use his average tailpipe one and downpipe into AFX/ECU from downpipe.

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Sat Nov 28, 2015 3:57 am
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Cheers Nige! I hadn't considered the low flow issue. A piece of straight pipe could be fine but would need to be impractically long to not suffer reversion, I guess. Once the unit arrives I'll play around a bit and do some drawings.

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Sat Nov 28, 2015 10:40 am
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Can't you take the "fast" one and put a thin rubber ring on the probe pipe ?
The rubber ring will close the main exhaust at low rpm and will flex away at higher rpm.
You could use EPDM (bicycle inner tube) up to 150C.


Wed Dec 02, 2015 5:46 pm
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You wouldn't get any flow at low RPM/load with that approach, would you? It'd go stagnant.

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Wed Dec 02, 2015 6:17 pm
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I'm thinking along this way, just a simple flat sheet of rubber closing the large exhaust but going around the small tube. Forcing al the gasses to go through the small pipe. Since its only a thin sheet of rubber it will flex at high RPM.
You would only need to cut one large, 100mm round sheet of rubber, and make a small 33.7mm hole in it for the sampling tube.


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Wed Dec 02, 2015 7:19 pm
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Ahh, clever idea, however I don't think I'd be comfortable with that tube unless it was a bunch longer.

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Thu Dec 03, 2015 5:59 am
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Just pulling a number out of my, ummm, 'ear', without doing any reading or math, I'd say you'd want that FAST toy to stick a good 2-3 feet past the sensor to avoid pulses sucking fresh air all over it.

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Sun Dec 06, 2015 5:49 pm
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3 feet would be quite clumsy if you'd actually drive the car on the street.
Can't you use a tapered reducer and reduce the tail end 2 pipe sizes ?
From dn25 to dn15 to pick up velocity of the gas stream? That could keep the outside air out.


Tue Dec 08, 2015 9:30 pm
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I would imagine that would increase pressure at the sensor element and possibly induce an imperceptible error in the process. Could help though, I guess.

In other news, the 14point7 gear arrived! Hope to have it in hand soon. :-)

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Fri Dec 11, 2015 6:09 am
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