02 sensor location on stock exhaust, where should I put it? Options

[monkeyboy]

I am installing an AFR meter to help me jet my carbs. Everything on the car is stock but the carbs. Since there really is no collector on the stock exhaust, where should I mount the O2 sensor for a decent reading?

Any suggestions?

[914werke]

Since we dont know what car you have IE engine / exhaust, it makes it kinda hard offering suggestions!

[monkeyboy]

Uh, oops...

I have a 72 with a 2.0 liter transplanted in by a PO. The exhaust is stock with the heat exchangers. It has the two tubes running down each side that dump directly into the muffler. Since there is no collector to put the sensor in. I am confused as to what would be the best place for it.

[nathansnathan]

I'm planning on welding bungs in each of the 4 tubes into the heat exchangers on my carb setup so I can dial them in individually - I can't see how just one at the collector would help very much when each barrel has it's own adjustment.

[monkeyboy]

I'm running dual 1 barrel carbs. I am trying something strange. I just want to make sure I am in the range. it doesn't need to be perfect.

[nathansnathan]

I tried to figure it out and learned a bit from a thread on thesamba, a guy trying the same on his bug.
http://www.thesamba.com/vw/forum/viewtopic...asc&start=0

The best bit

tzepesh wrote: I would say that correct results can be obtained only by placing the lambda probe after all pipes merge into one. I had some problems with mounting the probe in the exhaust pipe of only one cylinder, because it would have correct reading in only one of the 4 strokes (exhaust stroke). The other 3 strokes would lead to showing a lean condition, because the gas flows towards the muffler and it would cause a void. If the probe is placed after the merged pipes, it will get a continuous flow of exhaust gas, thus a correct reading.

-which means my 4 bung idea won't work, I think.

The consensus there is to use an extension fitting over the exhaust as that's the only place the 4 have come into 1 that can be accessed, but it needs to be extended to prevent false reading from air being drawn in.

The only such thing I could find is one on the bottom of this site
http://bugpatch.com/VWToolsCatalog/VWTools...79/Default.aspx

but it would be small as it's for a bug. I'f you've got the center exit early tailpipe maybe that would work on its own?

[monkeyboy]

Could I just put it in the muffler then?

[nathansnathan]

They were saying in the thread there that inside the muffler the flow isn't sufficient to get a fair reading, so I'd say no.

Incidentally, looking further for a way to check all the barrels, I've figured out it's not going to be cheap. Seems the AEM UEGO 4-channel wideband controller is the most affordable way at about $515!

Maybe try a Gunsen colortune (IMG:style_emoticons/default/biggrin.gif)

[monkeyboy]

I didn't think so either... So if I have headpipes that go straight to a muffler with no merge or collector, I'm screwed?

[nathansnathan]

Seems the tailpipe extender with a bung in it would work, even better to modify a tailpipe by welding an extension. I would think slip-fitting an extender over would be a challenge to find something the right size and wondering whether it was leaking. Other thoughts, beetle tailpipes are really short and come straight out. It might not be necessary on the 914 one to make an extension at all?
These are my mufflers, that tailpipe is for a snowplow through-hole valance, but the 1 for the cutaway is even longer I think.
(IMG:http://www.914world.com/bbs2/uploads_offsite/www.eggscollective.org-11782-1310588392.1.jpg)

[monkeyboy]

That's the same pipe I have... It may have to go there.

[mrbubblehead]

that looks like it would be best place. right at the end of the 45 degree elbow just as it exits the muffler and into the tail pipe. i will take pictures of my bungs and post them up for you guys. i have 5 total. one on each individual pipe and one right after the collector.

[mrbubblehead]

that looks like it would be best place. right at the end of the 45 degree elbow just as it exits the muffler and into the tail pipe. i will take pictures of my bungs and post them up for you guys. i have 5 total. one on each individual pipe and one right after the collector.

my main bung for my overall a/f meter is kinda hard to see because of the heat sink i made but it gives you an idea.....

[monkeyboy]

Nice. Thanks.

[mrbubblehead]

one thing you guys should remember, you should totally seal all exhaust leaks becuase it may effect your a/f readings.

[monkeyboy]

I am working on that. My exhaust is currently in the garage, and I have all new gaskets for it's reinstall.

[mrbubblehead]

i put my exhaust together with new gaskets also and still had small leaks. so i had to dissassenble it and use some high temp O2 SENSOR SAFE silicone. which sealed up them up real good. THENNNNN i had to weld up some tiny pin holes. but i got it done, and its totally sealed up now (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/piratenanner.gif)

[r_towle]

its not going to tune the carbs to well I am afraid.
Best way to do that is exhaust gas temp gauge with a sensor at each exhaust port....then you really know how each cylinder is tuned for the carbs.

Something like this from Foley
http://www.tangerineracing.com/engine.htm#...dCHTInstruments

Rich

[nathansnathan]

I wonder which would be better, the 4 channel egt or the 4 channel afm?

http://www.aemelectronics.com/wideband-air...-controller-60/

[ChrisFoley]

I wonder which would be better, the 4 channel egt or the 4 channel afm?

http://www.aemelectronics.com/wideband-air...-controller-60/

Neither.
The EGT is really only valuable if the engine spends a lot of time at WOT, ie. in a race car.
4 channel W/B AFM is overkill.

I get excellent carb tuning data from a single N/B AFM and 4 channel CHT.
Put your O2 bung after the muffler, at the beginning of the tailpipe. If the sensor is heated and its at least a foot away from the exhaust tip it should give good data.