02 sensor placement for standalone AF gauge

[inchoate]

one of the winter projects I'm kicking around is setting up a stand alone AFR gauge that can be used with my various carbureted vehicles.  I don't suck at tuning carbs but I feel like it would be nice to have some real numbers to inform my process.  If I go ahead and do this I'd like to weld a bung into the Caterham exhaust so I can do some road testing.  I'm thinking the best place is in the collector just upstream of the muffler.  Does that make sense?

 

 

Right about here.  

[7Westfield]

There will probably be some air sucked in where the primaries go into the collector, affecting your numbers

[wdb]

I guess I'm old fashioned. I've always gone with the color of the spark plugs. But this does seem like a nifty idea. The location looks logical and also possibly the only place to do it. As for air being drawn in, the result would be an artifically lean reading; I'd rather have my mixture richer than necessary than leaner, so... there's that.

 

I'm intrigued. Keep us apprised of progress please.

[MV8]

Leakage at the slip yoke should be sealed within a few minutes of running (outer tube runs cooler) unless there is a really sloppy fit. I'd put it in the collector.

[Vovchandr]

Do you have a hole for a downstream o2? 

[fastg]

Looks good to me, point it inwards as you can just get the sensor to screw in. The collector will have sealed, or do you see constant scooting around the primary tubes. Plug tuning is great with new plugs and full throttle, after a miles it's all over. With an O2 sensor you can tune the midrange, accelerator pump settings, even part throttle economy. O2 sensor is the way to go. 

 

Graham  

[S1Steve]

I can get a better picture in the morning if needed. I was told that’s the best place for the O2 sensor. So I drilled a hole and welded on a 316 Stainless bung…

 

Edited December 28, 2023 by S1Steve

[NSXguy]

Not the best photo, but you want the sensor mounted as vertically (upright)and as close as possible after the merged collector to get accurate readings. 
 

While more aesthetically pleasing, mounting the lambda sensor close to horizontal or worst under the exhaust pipe(sensor element facing upward) will result in fouling from condensation after many cycles. 

[inchoate]

I was thinking to mount it as close to vertical as possible.  The plan is to only have the sensor installed when I'm actively tuning.  I'll run it with a plug for day to day use so it's not too obtrusive.

 

Currently trying to  settle on an AFR gauge.  I don't need a whole lot of capability but it's tempting to future proof by getting a fancy one.  Lots of options out there.

[NSXguy]

1 hour ago, inchoate said:

I was thinking to mount it as close to vertical as possible.  The plan is to only have the sensor installed when I'm actively tuning.  I'll run it with a plug for day to day use so it's not too obtrusive.

 

Currently trying to  settle on an AFR gauge.  I don't need a whole lot of capability but it's tempting to future proof by getting a fancy one.  Lots of options out there.

 

I use the AEM 30-0300 X- series on mine. Comes with everything you need to install including the weld on bung. 
 

you can use it as you intend. I originally planned to do the same, but as an EFI guy… I came to enjoy being able to monitor my afrs on the fly. The unit also has data logging capabilities (needs extra work/wiring to implement)

 

also, in reference to your photo, you can mount it after the merged collector and after the slip on connection on the exhaust (that extra inch or 2) won’t significantly affect afr readings. 

Edited December 28, 2023 by NSXguy

[inchoate]

I'm leaning toward the Innovate MTX-L at the moment although AEM and Autometer are also possibilities.  Whichever one you look into you can find equal numbers of people that love them and hate them.

[NSXguy]

They all do essentially the same thing . Maybe a slight difference in fidelity of data, features and what is included in the package.

 

I have no recent experience with those two but both are reputable companies, so you should be fine with whichever you prefer. As long as it is not a narrowband sensor. I suspect they will all be using lsu 4.9 sensor elements or newer which is the way to go. 

[IamScotticus]

how about the sensor sizes and threads?  Is there a standard?  

Is there any thread difference between an AFR O2 sensor and a Lambda?

Can a Lambda be a stand-alone system?

This may help

https://lambdageeks.com/o2-sensor-thread-size/

 

Edited December 29, 2023 by IamScotticus

[inchoate]

I ended up going with the Innovate kit because it was slightly less expensive, it comes with a 4.9 sensor, will read in AFR or Lambda, and has a lot of extra data capability.  I don't think I'll need datalogging or anything like that for the 7 but it might come in handy for some other stuff.

[IamScotticus]

Did you get the 3ft or 8ft cable?

[inchoate]

I went with the 3 foot.  It's not getting installed permanently anywhere and I can always get a longer cable if it becomes necessary in the future. 

[IamScotticus]

Will you be able to watch it while driving?

[inchoate]

Should be able to.  I've got a small box of RAM mount parts and I'm pretty sure I can cobble something together that will allow me to suction cup it to the windscreen or something like that.  If I want to get fancy I'll set up a camera that can see both the gauge and the tach.  If I really go nuts I can set up some datalogging on a laptop, but that kind of defeats the purpose as I'm trying to keep this as simple as possible.

 

Also, as a general FYI, the Innovate sensor comes with a mild steel bung.  I'm mildly dead in the water while I wait for a SS one to show up.

Edited January 2, 2024 by inchoate

[slowdude]

Sorry to necro-post this. @inchoate, did you wind up going after the clamp? Or did you clamp and then use exhaust cement? How did you route the wiring?

[jbcollier]

Just a couple of points:

 

- no one can accurately tune carbs by ear and eye.  Take the case of the famous tuner (multiple Isle of Man winner) who set up his bikes for a sweet mid-range hit.  With a modern A/FR gauge, they found he tuned in a flat spot to create the "hit"!

 

- collector is the right spot, use a bit of sealer to make sure no false air is drawn in.

 

- the sensor wire needs to go up if it is a permanent install.  Just for testing a warm engine, it does not matter that much.

 

- DO NOT SET THE MIX TO THEORETICAL PERFECT (14.7:1)  That is way too lean.  Very low 14s to high 13s for light throttle.  Low 12s for WOT.  Lots of info online.  Older engines (insert Lotus TC and Ford crossflow) will especially not tolerate lean mixtures.