Pre or post turbo for wide and O2 sensor?

Is it better to place the wideband O2 sensor before or after a turbo or does it matter?

TurboFource said:

Is it better to place the wideband O2 sensor before or after a turbo or does it matter?

In principle it doesn't really matter, but it needs to be 4-6 feet from the engine unless you want to replace them every couple weeks.  Turbo engines have high EGTs and widebands are fragile.

In most situations that means it comes after the turbo, but I suppose if you had one of those remote mount kits that puts the turbo where the muffler normally goes then it would be in front.

I suppose every setup is a little different, but I would think downstream of the turbo.  The turbo manifold on my RX-7 would be an impractical place to put an O2 sensor.  The downpipe on the other hand works very nicely.

Thanks!

Turbos take a tremendous amount of heat out of the exhaust. So doing it just after is really good- let alone the turbo acts like a mixer to make sure the flow isn't biased to one side. 

Just as a data point, der Scheißwagen has some pretty serious EGTs and they mounted the O2 sensor on the top part of the downpipe, about 6 or 7 inches (if that) from the turbo outlet.  And while I don't know that you want to take too much engineering advice from our friends in Stuttgart, O2 sensors are not a common failure point.  On the turbo Neon, one of my O2 sensors is using the stock upstream sensor location which is right off the turbo as well and it doesn't seem to have problems either.

EDIT:  The Neon's O2 sensors are widebands (one for display and one for MegaSquirt) and based on the price of the Bosch replacement, I'm assuming that der Scheißwagen's is as well.

codrus (Forum Supporter) said:In principle it doesn't really matter, but it needs to be 4-6 feet from the engine unless you want to replace them every couple weeks.  Turbo engines have high EGTs and widebands are fragile.

If the sensors should be that far down stream why to manufacturers put them so close to the engin?  With some being in the manafolds  them self. I always thaught they need to be close to the engin. One reason is that it gets them up to operating temp faster and greatly reduces emissions at start up. BUT I can see the manufacturers sacrificing longevity for emission compliance.  
 

From my reading placement away from the collector or merge is much more important as you want complete mixing of the gasses from all cylinders and I believe you want a minimum of 18-24 inches of pipe after the sensor to prevent outside air from back flowing between pulses giving a faults reading.  
 

As for over heating them we test them with propane torches with no I'll effect so I am not sure of the clame that you can put them two close. If you put the so close that they are being over heated you will not be getting accurate readings as you will not have proper mixing of the gasses.  
 

A good article I found with some basic info. 
 

https://journal.classiccars.com/2019/03/11/tips-for-properly-placing-installing-an-oxygen-sensor/
 

After turbo

Not just heat but the readings will drift with pressure. You can get compensation curves for various sensors but you'd have to be doing the math in your ecu if you care about the absolute afr. Having multiple, pre-turbo sensors can be helpful for diagnosis or individual cylinder trims. If you are just comparing pre turbo between cyls and have a post turbo sensor for bulk reading you can make sense of everything.

My go-to is 6" from the turbo, or 18" from the port if not using a heatsink. Some of the sensors don't work well when too hot, but you can use heatsink bungs or sheets of copper between the sensor and bung to help. 

OEMs can put them in the manifold because they have good sensor thermal management.

Inexpensive wideband controllers do not have good thermal management.  After turbo and down the pipe a ways.

Also, many/most OEM sensors are narrowband, which are inherently much less fragile than widebands.  I killed multiple wideband sensors mounted 3 feet from the turbo.

Innovate's instructions say to mount it "at least 24 inches after a turbocharger", for example:

https://www.innovatemotorsports.com/wp/content/uploads/2022/05/SCG-1-Manual.pdf

codrus (Forum Supporter) said:

Also, many/most OEM sensors are narrowband

Post cat, yes. Precat, not sure if it's most of them, but a lot of them are wideband.

In reply to Paul_VR6 (Forum Supporter) :

I would venture that everything made in the last ten years or so is wideband, with widespread adoption before that.  I cannot remember the last time I saw anything that had a narrowband upstream sensor.

Having fine fuel control allows the converter to be a lot smaller, which saves space and money.

Pete. (l33t FS) said:

In reply to Paul_VR6 (Forum Supporter) :

I would venture that everything made in the last ten years or so is wideband, with widespread adoption before that.  I cannot remember the last time I saw anything that had a narrowband upstream sensor.

Having fine fuel control allows the converter to be a lot smaller, which saves space and money.

I was going to post the exact same thing. I know F went universally UEGO in the 2010 area. 
 

And they are not fragile at all- they can take the same abuse catalyst do- which is pretty rough- and getting rougher in the near future. 
 

codrus (Forum Supporter) said:

Innovate's instructions say to mount it "at least 24 inches after a turbocharger", for example:

https://www.innovatemotorsports.com/wp/content/uploads/2022/05/SCG-1-Manual.pdf

 

I think we've established that the problem comes from innovate and not the sensor. 

I have had NGK sensors in the manifold 1" from the port on turbo cars freak out. Heat is real when you are making jam.

Agreed on the innovate issue not being sensor related.

"24 inches after turbo"  will almost be behind my Europa .....I will probably put it in the downpipe, thanks for all the advice!

never heard of it being anywhere but after the turbo