Interesting Fact About Putting Wideband In The Tailpipe

[Rolls]

So I heard this through the grape vine from someone at motec, it makes sense now that I think about it but I wonder how often it is overlooked. The exhaust gases in your exhaust take about 3 seconds to reach the muffler from the turbo outlet. It is obviously a function of exhaust gas pressure, exhaust size etc, but on the race car they were talking about it would take roughly this long.

That means you really need to calibrate your tuning software for this lag as it is going to mess with your maps if aren't aware.

[Roy]

3 seconds? I think things are happening far quicker then that. Most of the good tuners I know about tune off a bung in the dump pipe before the cat. They would readily be able to equate instrument readings for those customers off the street who dont have their car fitted with a bung so not a big deal to stick it up the muffler

[Rolls]

Well it was someone from motec so that gives it some merit. I personally haven't ever experimented eg running real rich then normal and looking at the graphs to see the lag.

I imagine there would be some lag, how much I guess you'd have to try and see.

Anyone want to test this out? I'm curious how close it is.

Edited January 17, 2012 by Rolls

[jiffo]

A bung in the dump is the preferred option for most tuners.

Makes the road tune touch up much easier too, no long cables dragging out the back.

[JustinP]

Surely a 3 second delay (if correct) would only be true at idle?

I'm sure it would be negligible at full revs / boost!

So I heard this through the grape vine from someone at motec, it makes sense now that I think about it but I wonder how often it is overlooked. The exhaust gases in your exhaust take about 3 seconds to reach the muffler from the turbo outlet. It is obviously a function of exhaust gas pressure, exhaust size etc, but on the race car they were talking about it would take roughly this long.

That means you really need to calibrate your tuning software for this lag as it is going to mess with your maps if aren't aware.

[Rolls]

Well lets prove him wrong then, who has a wideband here?

[JustinP]

I've also wondered if the cat would have an effect on readings?

Well lets prove him wrong then, who has a wideband here?

[jiffo]

Oxygen sensor is constantly comparing oxygen levels inside the pipe against the air outside.

Sensor in the dump eliminates any chance of contamination from stray exhaust.

Car in a dyno cell with that big fan working can have some dead air around the rear bar so probably not the best spot for the sensor even though it is the easiest.

[rondofj]

When I had my car road tuned, it was running lean no matter what my tuner did with the maps. We really thought it had to be the fuel pump.

Took it to dyno, had fuel pressure gauge hooked up and its running nice and sweet, ideal fuel pressure 43psi I think, no lean issues. Had it tuned on dyno nice and well.

Took it once more to the road to check AFRs and that everythings ok. Car runs really amazing after the tune but... guess what, afrs were screwed again, running lean on the road. The wideband sensor was straight off the tailpipe.

Back to workshop, scratching heads, then the workshop owner suggested to use his bung - basically now we connected the wideband to a roughly 20cm long metal tube and clipped the whole thing back in the tailpipe - dont ask me how, I dont remember lol..

Out on the road again and....absolutely brilliant AFRs (no leaning whatsoever) - as witnessed on the dyno during tuning...We are like WTF? That little metal tube made a huge difference to the sensor's readings. I think it was because of my XForce oval exhaust which has a

perforated metal tip and insides where the sensor was mounted - this possibly messed with the exhaust flow / turbulence and increased the air supply (outside air??) into the sensor, hence lean out issues.

The pipe possible solved that as it was not perforated like my exhaust tip and walls inside.

But yeah, this was definitely an issue that my tuner never had with any car before...

Lesson learned - Use a pipe in your exhaust and put your wideband in it. Or better still, make a bung in your dump for the wideband which is what he recommended.

[TiTAN]

3 seconds? I think things are happening far quicker then that. Most of the good tuners I know about tune off a bung in the dump pipe before the cat. They would readily be able to equate instrument readings for those customers off the street who dont have their car fitted with a bung so not a big deal to stick it up the muffler

my wideband is in my front pipe ~20cm infront of the cat, it changes ~2 seconds after throttle changes which does cause a little bit of hunting at idle (low gas speed this does not apply to high load, more revs/boost the faster it is), but you also have to take into account that your ECU (unless told to) does not make BIG changes to the fuel map and most tuners wont have it operational during high load/boost anyway.

[DVS JEZ]

On the dyno when tuning from tailpipethe lag can be accounted for when holding steady state.

Ecu's with Constant feedback / correction is normally bunged into the dump pipe before the cat

[gotRICE?]

Well lets prove him wrong then, who has a wideband here?

I have one available to me that i could borrow for a few hours.

Actually now i think of it, its one of those ones that can be used to tune V8/V6 with two sensors and inputs. I wonder if the cable would be long enough to put one in the tailpipe, and one in the dump pipe, Would that not prove if there was a difference? Same exhaust gasses being measured twice at different locations.

Actually, 3 times. As i have my wideband permanently mounted in my de-cat and wired into the G4, and i have a spare bung in the dump for using dyno widebands.

Could be an interesting result.. or a boring one. Ill see what i can do.

Edited January 18, 2012 by gotRICE?

[Rolls]

That would be a fantastic test gotrice! would love to see the difference in both AFR measured and lag.

Please do it.

A graph with all 3 overlayed at idle and say reving out 1st or 2nd gear would be the most interesting, higher gears would be slower so any lag would be compensated for by being closer to steady state.

Edited January 18, 2012 by Rolls

[gotRICE?]

Righto ill see if i can check it out in the weekend and report back.

[Rolls]

Would definitely be of great benefit to the at home tuning community on here with to see what kind of difference is to be expected in both AFR and lag time.

Can't beat real world results at the end of the day.

Thanks!

[Adriano]

When I had my car road tuned, it was running lean no matter what my tuner did with the maps. We really thought it had to be the fuel pump.

Took it to dyno, had fuel pressure gauge hooked up and its running nice and sweet, ideal fuel pressure 43psi I think, no lean issues. Had it tuned on dyno nice and well.

Took it once more to the road to check AFRs and that everythings ok. Car runs really amazing after the tune but... guess what, afrs were screwed again, running lean on the road. The wideband sensor was straight off the tailpipe.

Back to workshop, scratching heads, then the workshop owner suggested to use his bung - basically now we connected the wideband to a roughly 20cm long metal tube and clipped the whole thing back in the tailpipe - dont ask me how, I dont remember lol..

Out on the road again and....absolutely brilliant AFRs (no leaning whatsoever) - as witnessed on the dyno during tuning...We are like WTF? That little metal tube made a huge difference to the sensor's readings. I think it was because of my XForce oval exhaust which has a

perforated metal tip and insides where the sensor was mounted - this possibly messed with the exhaust flow / turbulence and increased the air supply (outside air??) into the sensor, hence lean out issues.

The pipe possible solved that as it was not perforated like my exhaust tip and walls inside.

But yeah, this was definitely an issue that my tuner never had with any car before...

Lesson learned - Use a pipe in your exhaust and put your wideband in it. Or better still, make a bung in your dump for the wideband which is what he recommended.

Before you tried the pipe, how were you mounting the sensor? Or was it swaying in the breeze?

No way it is 3 seconds at full load, otherwise power runs wouldnt log even close. Old sensors are slower than new ones, and at idle mine is probably 2 sec difference between dump pipe and tailpipe.

[Rolls]

It is a factor of load as well adriano, eg if you are dynoing full load in 4th gear then it is going to be almost 1 second between load cells anyway.

I'm guessing but I would say if it is an issue, it would be at low load levels when road tuning eg 1st and 2nd gear.

[KiwiRS4T]

I have an extra bung for tuning but I am sure that experienced tuners who come across people who don't want to pay for an extra bung will have worked out if there is any correction necessary for measuring at the tail pipe.

[Rolls]

Would be curious to hear STATUS' opinion on this.

[rob82]

Hmmm - OEM's have been accounting for this for years - Ford term it "02 sensor Transport delay". These tables have been used since ed falcon!