[Glavey]

Hey dudes and dudettes, how are ya?

My current EFI project requires an O2 sensor bung to be welded to an exhaust system... on a 50cc engine. You can imagine how small that exhaust pipe is. If you can't, it's about 23mm or 9/10 In. OD.

Question 1; With said tiny pipe, should I buy a stepped/tall/angled/normal bung?

Question 2; If I buy a weld-on bung and bring it and the exhaust pipe into a muffler shop and ask them to weld on the bung, are they going to tell me that the pipe is too small to weld onto and laugh their arses off after I leave?

[dazq]

I think you need to get a longer bung to spacer the tip of the wbo2 tmso it is just sticking into the flow of gases. You can get extension adaptors so maybe you can modify one of those the make a bung of the right length.
This should minimise any flow restrictions

[wt29]

Late reply but I have a Wide-Band O2 on a 125cc pipe. My mate milled a hole and welded with no significant issues. Just make sure the sensor is on the "top" of the pipe once positioned on the engine. You need to ensure that condensation during start up and once the engine is shutdown, won't drip on to the sensor as it will ruin it.

[PSIG]

We've used "Spark Plug Anti-Fouler" extensions and ground them for a mitered fit for welding. Most auto parts stores have them for about $10. Take your sensor with you to verify you get one long enough to mod. 18mm thread like the sensor.

I would place it at the end of the straight-tube section in order to help maintain any tuned-pipe effects. I would not place it too far back to ensure it doesn't suck any air back past it during exhaust pulse reversion. Good luck and post pics!

David

[motzingg]

A few years ago i got to run on a dyno at a shop owned by a friend of a friend, he tunes 150+ hp liter bike race engines and had a super clever device made out of a vacuum pump, a jar (yes a literal mason jar) with a aluminum lid on the top with fittings and a bung for an 02 sensor, and a 'sniffer' that was just a 1' long piece of brake line on the end of a hose connected to the jar.

He could quickly and easily stick the 1' section of hardline up the tailpipe of a bike running on the dyno, do the dyno pull, and swap to another bike without having to drill in bungs or mess with the ECU on the bike loosing its main 02 signal.

I was thinking about doing something similar for moped engines that i work on, but haven't got around to building one yet. Also i don't have a dyno but i have a project in the works.