Best Location for AF Sensor Bung, UPDATE: I got a SS muffler, what you all say now... Options

[913B]

I am going Microsquirt. My current muffler right before I tried cleaning the dust off the part label and it just incinerated is a Dansk 1.8 muffler from what the PO said.
I did have to reweld and rotate tip to exit correctly under the valence.
Maybe it was a bus muffler?

Anyone have any experience on where to place the AF sensor bung, too bad its not on the car to check for clearance/obstruction issues.

I was thinking of welding it on the tail pipe where the black circle I marked off.

I could buy a new exhaust with the bung attached, but this is my attempt at going Microsquirt without spending too much and work with what I have.

Anyone cut one up before and know of a good spot?

Thanks in advance.

Ted

[emerygt350]

You are going to want it closer to the heat I think. Mine is right at the collector but it is an ansa so it was easy. You don't really have that on that muffler.

[BeatNavy]

I've been running Microsquirt for a couple of years now. I don't have experience with that specific muffler, but if I had to guess the place you propose is as good as any. I'm always hesitant to drill into the "body" of the muffler for fear of upsetting the internals, and you don't have too many options there. I'm sure others can provide more specific guidance.

Yes, clearance is an issue to be concerned about. Take into account not just the sensor but the cable and the fact that you have to get it all lined up to thread it into the bung. That means you either need more space than you may realize or you have to remove the muffler before installing/removing the sensor.

Running Microsquirt in closed-loop on a type IV can be a little tricky, particularly at idle. Idle AFR numbers can be misleading on our motors due to a number of factors. I initially ran closed-loop using a stainless steel, dual-tip muffler sold by a vendor here. It had the O2 sensor bung pre-installed, presumably in the "best" location. It is a great muffler, but for whatever reason I could NOT get usable AFR numbers at idle. Always showed way too lean and had me chasing my tail for months. Above 1500 RPM or so it was fine and closed loop worked great, but idle was useless.

Eventually I switched to another vendor's muffler, with single-tip, and voila', my AFR numbers at idle were useful.

So: make sure you heat exchangers/headers aren't leaking at the heads. Make sure your muffler is not leaking at the heat exchangers. And don't drive yourself crazy chasing a specific idle AFR or closed loop setup at idle if it just won't happen with this muffler.

[StarBear]

This bung may be my next project - maybe this coming winter.
Very timely!

[76-914]

Within 12" of the header. If installing on a horizontal tube be sure to located between the 10:00 & 2:00 o'clock positions to avoid moisture collecting in the sensor. (IMG:style_emoticons/default/beerchug.gif)

[StarBear]

Within 12" of the header. If installing on a horizontal tube be sure to located between the 10:00 & 2:00 o'clock positions to avoid moisture collecting in the sensor. (IMG:style_emoticons/default/beerchug.gif)

Great tips (pun intended). Thanks!

[technicalninja]

WB O2 sensors are heated and can be placed anywhere in the system.

On a turboed car we put them at least 18" down the exhaust system as the heat can shorten their life.

Any sensor in the exhaust system should be "in the roof" as water is a significant byproduct of an ICE engine.
1 gallon of fuel burned equals approximately 1 gallon of water output. Some sources say more!

The only place that both sides come together is internally in the muffler and at that tip.

The tip looks fine with one exception...

Any negative pulses (shitloads in an exhaust system) will pull clean air UP that tip and it will probably read leaner that it actually is...

Does someone have a cut-away picture of the inside of a log type muffler?

Where the two sides come together internally in the muffler is where I'd want my sensor. Placing the sensor in a primary will only show that cylinders AFR. Placing at tip may yield in-accurate results.

Really serious folks will put one in each primary with individual EGT probes as well.
Car ends up looking like a science experiment...

One work around might be to lengthen the tip. I don't know how long it needs to be but I would think something 24" long would tend to reduce the fresh air pull that can happen.

The short tube effect on the sensor would be more prevalent at low engine speeds IMO.

[Superhawk996]

One work around might be to lengthen the tip. I don't know how long it needs to be but I would think something 24" long would tend to reduce the fresh air pull that can happen.

Something like this ought to work - ideal location circled / red arrow



No offense to anyone - just having some fun (IMG:style_emoticons/default/av-943.gif)

[technicalninja]

Superhawk, your car would look great in leopard print with a Bosozoku pipe. (IMG:style_emoticons/default/aktion035.gif)

Years ago, before WB02 sensors existed, the proper tuning tool was a Horiba 5 gas analyzer. This puppy cost 10K+ in the eighties and was the size of a microwave.

The probe was not cheap either and we would plumb the probe leads through the trunk/rear of car and clip the sensor as deeply into the exhaust pipe as possible.

It worked pretty well above 2K rpm but wasn't worth a shit at idle due to "free air" entering the tip.

God, I don't miss those days...

$200 gets you the whole shebang now (and it reads a real AFR number, Horiba did not!) and the new ones can both be controlled by and talk to the digital FIs of today.

I would not USE a stand-alone that didn't require a WB02 to operate.

Link to a much more modern Horiba than I used. Mine had needles!

https://www.ebay.com/itm/394364285905?chn=p...AyABEgJFQfD_BwE

Still BIG and expensive!

[Superhawk996]

Still BIG and expensive!

Child’s play.

You need one of these!



I used to work with Horiba off and on in Detroit both for contract dyno testing and once when the company I was working for at the time was looking to upgrade its dynos.

[914werke]

You'll be money ahead replacing that with an different/better muffler like a Bursch.

[913B]

Dang a Horiba $2999, new Bursch exahaust $899!!

[technicalninja]

And remember that Horiba is USED!
Parts for it may be "Hens Teeth"!

I've got what I believe is a Bursch copy that extends the primaries into a 4-way flange and has a single tube into a simple muffler. That tube is where I'm putting my sensor.

So, a good answer from me on where to place the O2 sensor bung is after the primaries have come together, before the muffler section, as far away from the heat as possible, and mounted in the roof of the pipe.

If I had 3K to spend on my 914s exhaust I'd just hit up Chris Foley as his systems look perfect to me, opposing cylinders are paired, clean collectors, and his O2 sensor bungs are in the right place. Nice stuff in my book.

That's where I'd put 3K...

[914werke]

Dang a new Bursch exahaust $899!!

the new ones are Stainless, (IMG:style_emoticons/default/shades.gif) If budget conscious look for pre-owned should be in the 2-$300 range

[pilothyer]

Dang a new Bursch exahaust $899!!

the new ones are Stainless, (IMG:style_emoticons/default/shades.gif) If budget conscious look for pre-owned should be in the 2-$300 range

Where would the best place to put the bung on that Bursch ??
Could you mark it on the picture (Please??)

[technicalninja]

I'd put it in the final collector where the two tubes come together pre-muffler or in the section of single tube directly after the merge but before the muffler.

That final collector has a nice flat spot for welding on a bung...

I like that version better than others. It appears to have opposing cylinders merging together first and then a merge from the paired cylinders.

It might have two negative reflections in operation. See Tri-y exhausts for the V8 versions of for explanation.

Two collectors should create two negative scavenging "waves" at different RPMs to assist with cylinder filling.

I like multiple collectors. (IMG:style_emoticons/default/first.gif)

[burton73]

I'd put it in the final collector where the two tubes come together pre-muffler or in the section of single tube directly after the merge but before the muffler.

That final collector has a nice flat spot for welding on a bung...

I like that version better than others. It appears to have opposing cylinders merging together first and then a merge from the paired cylinders.

It might have two negative reflections in operation. See Tri-y exhausts for the V8 versions of for explanation.

Two collectors should create two negative scavenging "waves" at different RPMs to assist with cylinder filling.

I like multiple collectors. (IMG:style_emoticons/default/first.gif)

Rick,

This is where PMB Performance put the O2 bung on Factory heat Exchangers on my 6 when we changed to EFI
Just so you could have a look see.

Bob B

[technicalninja]

That location is EXCELLENT!

You are going to need two sensors with that system...

Bob, your stuff is always world class!

[VaccaRabite]

When I had the Triad exhaust on my car adding the 02 bung was so easy. They have that nice fat pipe right in the center that can sniff everything.

When I went to Ben's "Quiet" muffler I put the bung on top pf the tail pipe exit - and that DID work, but was not ideal. On overrun you could get reversion and get false lean readings while the muffler was sucking in fresh air from the tailpipe.

For my current engine, I am only sampling from pipe #3 just past the heater jacket, on top of the heat exchanger. Plenty of space there for the 02 sensor. No, it does get all 4 cylinders, but for tuning purposes its seems to be doing just fine, and for just monitoring AFR when driving there are zero issues.

Zach

[JamesM]

Best location with your current muffler would probably be directly above the passenger side flange but what I would recommend is just pick up a used Bursch and install the bung right after the collector. Use this to setup your tune and then switch back to your stock muffler when done, running in open loop.

The Bursch has enough back pressure after the collector to keep fresh air away from the sensor at idle. You might be ok with your stock muffler but there is also a high chance you will get false lean readings at idle and lower RPM. I have seen this with quite a few mufflers.