AFR changes with Zork

[6771911esses]

I recently removed my Borla exhaust and installed a Zork tube. Where the car ran 11.8 AFR on the wideband with the Borla I now see 13s. I read somewhere that this can happen with turbos with no restrictive mufflers. Any thoughts on this? Should I readjust my Leaske WUR or keep it at the same settings . The AFR sensor is upstream from the turbo and most tech articles I read recommend the AFR probe to be installed downstream from the Turbo. This would be in the Zork tube. My headers have the bung in the collector under the Turbo (like the factory O2 sensor) as most other 930 headers have it. Does anyone have their AFR sensor downstream from the Turbo?

Thanks

[Groovie Ghoulie]

Bump for answer. Need to install an AFR Gauge myself, but also want to keep my zork. Interested in the answer....

[sundevil64]

Subscribed. Currently tuning with a zork. Curious as to why if this is the case.

[Dave 86 930 Fl]

My AFR sensor is installed downstream of turbo ... I've never experienced a change in AFR as a result of muffler change. I'm currently running a zork and no issues with sensor performance.

[RarlyL8]

If you have not done so the change should be verified by putting your muffler back on.
O2 sensors located before the turbo are exposed to back pressure which can skew the reading. Locating in the tailpipe should provide consistancy to the reading nomatter what muffler/zork is used. If the muffler is restrictive the AFR's will be affected as you make more power.

[Miguel Antonett]

I had the O2 sensor upstream of the turbo for a while, then installed a new straight pipe exhaust with the bung right after the turbo with no difference in readings.
I wonder if the Zork tube is too short to install the sensor downstream of the turbo allowing - under certain conditions/ back pressure - some outside air back in indicating a lean mixture...

[s5uewf]

Some sensors/gauges need to be recalibrated from time to time, as well. If you de installed and re installed, etc. you may need to re calibrate. It should be in your manuals if your product requires it.

[JFairman]

Originally Posted by Miguel Antonett

I had the O2 sensor upstream of the turbo for a while, then installed a new straight pipe exhaust with the bung right after the turbo with no difference in readings.
I wonder if the Zork tube is too short to install the sensor downstream of the turbo allowing - under certain conditions/ back pressure - some outside air back in indicating a lean mixture...

Is your's a narrow band or wide band sensor?

It's wide band sensiors that are thrown off by backpressure. Narrow band O2 sensors like the factory '86 on lambda O2 sensor don't care about backpressure.

[RarlyL8]

It's wide band sensors that are thrown off by backpressure. Narrow band O2 sensors like the factory '86 on lambda O2 sensor don't care about backpressure.

Great point Jim, and the reason why the Lambda sensor is located before the muffler in the Carrera and the same spot in the 930. I believe Miguel has the same narrow band unit that I did in that spot. For such limited functionality it worked very well as a diagnostic tool.

[PrimeMvr]

Back in my youth when we'd put a free-flow header and pipe on a sport bike we'd also re-jet the carbs because the decrease in back pressure made for better combustion chamber scavenging, causing a lean condition. Tuning was a riot. We didn't know crud about using a gas meter, so we changed jets based on the amount of pop when speed shifting. I'm shocked we never burned a piston!

I have my wideband just after my muffler about 18" from the tip, and it reads very consistent. Some say free air can come back up the tip and give a false lean reading, but I find that hard to believe. There is a ton of mass flowing out the pipes even at idle.

[Miguel Antonett]

Originally Posted by JFairman

Is your's a narrow band or wide band sensor?

It's wide band sensiors that are thrown off by backpressure. Narrow band O2 sensors like the factory '86 on lambda O2 sensor don't care about backpressure.

Brian is right, I had a narrow band installed upstream of the turbo; then, Brian insisted on a new muffler - great guy! and I swapped the muffler with one with a different bung location downstream of the turbo - no change in AFR. After that, I got a wide band gauge and did the same back and forth with no change. BTW, with the wide band gauge, there is no need for the dyno to be able to play with the car... the way to go!

[cole930]

Don't know if this will be a help to you of not but this is how Brian
and I fabribated the Zork for the Old Sled. Note we added a heat sink
on the bung.









Cole