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Discussion Starter · #1 · (Edited)
Where to mount my wideband AFR bung?

I removed my stock downpipe from the turbo back to the end of 2nd cat. I'm replacing it with a 3" SS Hi-flow catted downpipe from CP-e. Like most of my other mods, I've had the parts just waiting in a box for me to have enough time & be up to the challenge of installing them. The particular challenge on this mod was removal of the factory studs & nuts that thread into the turbo allowing the downpipe to mount up. I was able to remove the 2 lower studs & nuts without too much difficulty after lubing with PB Blaster. But, I was only able to remove the nut of the top stud & the stud remained seized. I plan on installing the new downpipe securing it with only two SS studs & nuts, keeping the upper original stud in place. Then I plan on driving straight to the exhaust shop of my choice to have them remove the last stud & install the final SS stud & nut.

While there I will have them install the bung for my AEM wideband AFR gauge, but I've run into a problem. The instructions for the AEM AFR gauge state: "Mount the O2 sensor in the exhaust system at leas 18" downstream from the exhaust port. If you anticipate high EGTs (over 800c), running a turbo charger, run at high RPMs for extended periods of time or plan on running leaded race fuel then you must mount the sensor at least 36" or more downstream of the exhaust port as all of these can cause the sensor to overheat. On turbocharged engine the UEGO sensor must be installed after the turbocharger, if not, the pressure differential will greatly affect the accuracy of the unit. For accurate reading, the sensor must be mounted before catalytic converters an/or auxillary air pumps." It goes on to discuss angle of mounting etc....

My concern is that I want to mount the wideband sensor in the best possible spot available for the most accurate readings. But, the instructions state to mount the sensor prior to the converter, yet mount it 36" from the exhaust port. The CP-e Hi-flow integrated cat is mounted fairly close to the turbo side of the downpipe & will not allow for 36" of distance of distance from the exhaust port as recommended if I'm to remain in front of the cat. So, do I stick with the 36" recommendation from AEM & mount the bung far away from the exhaust port to reduce the chance of overheating the sensor or do I mount it in front of the cat in order to get the most accurate readings, but taking a gamble on overheating the sensor?

Thanks in advance for any insight & advice.



 

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well your not gonna be WOT all the time even at the track so i wouldnt worry to much about over heating it.. hmm i would have too look at it i guess.
 

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Discussion Starter · #6 ·
Thanks for the suggestions guys. I'm leaning toward right after the Hi=flow cat in the downpipe near the downstream O2 sensor.

For those not familiar with CP-e downpipe;

I have the CP-e catted downpipe, so there is no 2nd converter. The 1st O2 sensor bung is about 5" from the turbo exit point at the start of the vertical drop. Then the Hi-flow cat is one inch further down the vertical path, followed directly by the 2nd O2 sensor bung still vertical. Two inches further down the pipe it turns to horizontal with the flex section of the pipe, which accounts for 6" of length. The rest of the pipe is horizontal & connects with the other section of horizontal pipe by way of V-band. At the end of this pipe is where the cat-back mounts up & is where the 2nd cat used to be.

So, if I follow the AEM wideband directions & stay prior to cat for best readings, I will only be about 6" away from the turbo & maybe a foot away from the exhaust port. But, will be submitting my sensor to more extreme heat. Then again, this is where the upstream O2 sensor bung is welded in place by CP-e. I can choose right after the cat near the downstream O2 sensor & still be vertical avoiding additional water from rain etc, which will put me 16" from turbo exit & about 22" from exhaust port.

Of those of you that have installed wideband bungs after your primary cat in your exhaust, how are the readings? Pretty accurate?

Because I will be using this info to stay within limits for my bolt-on mods. I plan on adding a fair amount of air flow in & out prior to having a tune. I want to check after each mod to ensure I'm not running to lean before continuing on. In case you are wondering, I'm doing this to acclimate myself to the power increases slowly for ease of learning at the track.

Thanks again for your response



 

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I've got mine about 18" after the turbo and it's just fine. The bosch WB O2 sensors are pretty durable but they are also pretty cheap to replace so I wouldn't worry so much about it being exactly 36". If you're running cat(s), definitely place it before the cat(s), if not, then get as close as you reasonably can to the recommended 36" away from the turbo. It's a good idea if you're not planning on using the wideband all the time to remove the sensor when possible and stick a bung plug in there to extend the life of the sensor. Again though, the replacement bosch sensors are ~$30 so it really depends on your planned usage and penny-pinching preferences.
 
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