Wideband sensor location?

Odd question does it really matter where in the exhaust stream the wide-band 02 sensor goes. I have a bunch of classic cars to tune over the next year and was wondering if I could simple make a stand alone system that I just throw as far up the tailpipe as possible run the wire into the car to a guage and do some under load tuning that way.

Dropping a bung on say 7-8 cars is to difficult and honestly would require pulling a few eninges out slightly with the puller to get access.

The only problems with putting it downstream of the usual collector location is that there's more opportunity for exhaust leaks to mess with the reading, and it will take longer to warm up if it doesn't have a built-in electric heater.

I've seen dyno's use the sensor up the tailpipe thing.

The one time I had instrumentation vs. that- the TP reading was one a/f too lean- as it mixed a lot.

Can I go right at the top of the header, I can get to that on 90% of the cars. Then remove the sensor and cap the bung in the header?

Summit has bungs with caps for like 8$ which is dirt cheap.

You could do that, but you then run the risk of overheating the sensor and your readings being skewed by per-cylinder anomalies.

I use one of these exhaust clip ons designed for the task

With an Innovate LM-2 handheld for tuning the vintage stuff we build here.

I like it. Going down the road it never flutters.Nice steady readings

GameboyRMH wrote: You could do that, but you then run the risk of overheating the sensor and your readings being skewed by per-cylinder anomalies.

The sensors are good to 950C. And I suspect that you would not be running the calibration of whatever you are tuning to that tight of tolerances.

I just put one on the Mini. I took a piece of exhaust pipe and basically just extended the tip by 8" or so. I put a bung in the new pipe, and it clamps on. No leaks and the sensor is far enough up the pipe that it shouldn't cause any mixing. Of course, I'm tuning a carb so I know I won't be all that accurate anyhow

Don't put it downstream of a cat.

Keith Tanner wrote: ...Don't put it downstream of a cat.

That's funny. I can just see it "No matter how rich I set it, the O2 reading doesn't change, but the cat turns orange..."

alfadriver wrote:

GameboyRMH wrote: You could do that, but you then run the risk of overheating the sensor and your readings being skewed by per-cylinder anomalies.

The sensors are good to 950C. And I suspect that you would not be running the calibration of whatever you are tuning to that tight of tolerances.

Yeah I wouldnt be so much worried about that as compromising the strength of the manifold maybe.

Keith Tanner wrote: Don't put it downstream of a cat.

Why not? While you can't really do fast and dynamic a/f calibration there, the reading is just fine.

We do that pretty often.

It was my understanding that it leaned out the mixture. Heck, you use a downstream O2 sensor to check if a cat is functioning, what are you actually looking at there?

It will show leaner post-cat, but it should still change as the mixture changes, so the data isn't totally useless. The built in cat check is looking mostly for a difference pre vs post cat.

Since the newest car is from 1957 cats are the very least of my worries.

Thanks guys.

Keith Tanner wrote: It was my understanding that it leaned out the mixture. Heck, you use a downstream O2 sensor to check if a cat is functioning, what are you actually looking at there?

It does not. It does remove the remaining O2, sure, but while most see the sensor as an O2 sensor, the actual physics if the sensor reflects a ratio of oxidants to reductants. Normally, I see it slightly richer after the cat- moreso for a new catalyst.

When you run rich, it will see that rich just fine behind the cats.

Interesting, thanks.

rslifkin wrote: It will show leaner post-cat, but it should still change as the mixture changes, so the data isn't totally useless. The built in cat check is looking mostly for a difference pre vs post cat.

No, it's used for control. Has been for at least 15 years for most, if not longer.

Some will argue that it's primary job is to be a catalyst monitor, but I'm more on the side of very good air fuel control for emissions.