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Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Mon Oct 30, 2017 4:23 pm
by joe 90
Changes to timing cause changes to EGT and it's the difference in EGT which upsets the WD but only if it's a cheap one.


That was the original argument with the NB (which I still use alongside a WB).......the hotter they get, the leaner they read.
Likewise when you add a manually controlled WI system (MAF based EFI), as soon as it's activated, the AFR numbers displayed change.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Oct 31, 2017 10:32 am
by Tuner
When changing timing, nothing is "upset" but the curiosity of the observer, physics and chemistry are not "upset".

Changing timing changes the amount of NOx. The WBO2 sensor responds to NOx as if it is 50% as much O2. Anything that changes the amount of NOx has that influence independent of the actual A/F, separate from and in addition to the normal influence of A/F on NOx. On the lean side of 1 Lambda the NOx increases proportionate to the excess O2, so the deviation from true A/F is more pronounced further from 1λ.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Oct 31, 2017 11:10 am
by andyf
Tuner wrote:
Tue Oct 31, 2017 10:32 am
When changing timing, nothing is "upset" but the curiosity of the observer, physics and chemistry are not "upset".

Changing timing changes the amount of NOx. The WBO2 sensor responds to NOx as if it is 50% as much O2. Anything that changes the amount of NOx has that influence independent of the actual A/F, separate from and in addition to the normal influence of A/F on NOx. On the lean side of 1 Lambda the NOx increases proportionate to the excess O2, so the deviation from true A/F is more pronounced further from 1λ.
You might be on to something. I know that NOx changes with timing but I hadn't considered the thought that the wideband was sensitive to NOx. Guess I don't know enough chemistry to really understand what is going on in there. I suppose if the wideband chemistry is looking for O2 then it might also react to NOx. That would explain why on the rich side of the curve the wideband is sensitive to changes in the exhaust chemistry even if the actual air fuel ratio hasn't changed.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Oct 31, 2017 11:41 am
by Tuner
It also may explain why high and extremely high compression engines (which coincidentally have large valve overlap short-circuiting O2 through the chamber) will appear to run well with A/F most people consider "extremely lean" or "too lean".

I've done several street driving tuneups on engines which like it in the 16~17/1 range in mid-load part throttle acceleration. They actually improved mid-pedal response on the lean side of 1λ and markedly so as they became leaner and got further away from the sluggish characteristic of "too rich". On the other hand, some engines turn stupid at 16/1.

Obviously, on the lean side of 1λ the exhaust contains hot O2 (and more hot O2 the leaner it is) so up to the lean misfire point (which depends on distribution) more hot O2 improves combustion.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 01, 2017 12:09 pm
by andyf
Another good thought. I know that I've tuned some race engines to be way leaner on the wide band than most people are comfortable. But the power kept going up and the plugs looked good and the exhaust ports had a nice color so why not. Could be that some air leaking thru during overlap was confusing the wideband and providing a false lean reading.

I do like widebands but they are obviously optimized around controlling an OEM engine rather than a racing engine so not a big surprise that they provide some false data when used outside of their comfort zone.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 01, 2017 5:22 pm
by MadBill
A comparison between flow meter-calculated and WBEGO read out AFR numbers as the mixture is leaned out might be informative, especially if the dyno was set for step-tests, with time enough to stabilize flows at each point. :-k

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 01, 2017 7:13 pm
by andyf
I've never been able to get the wideband and the flow meter info to tie out. The calculated AFR is almost always a few percent different than what the wideband says. The calculated AFR is always higher on our dyno. I've calibrated the fuel flow by using a jug and a stop watch so I know it is accurate, but I don't have anyway to calibrate the air turbine. I also do not have anyway to confirm what the wideband says. We can do a free air calibration but after that I'm lost.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 01, 2017 9:28 pm
by Warp Speed
andyf wrote:
Wed Nov 01, 2017 7:13 pm
I've never been able to get the wideband and the flow meter info to tie out. The calculated AFR is almost always a few percent different than what the wideband says. The calculated AFR is always higher on our dyno. I've calibrated the fuel flow by using a jug and a stop watch so I know it is accurate, but I don't have anyway to calibrate the air turbine. I also do not have anyway to confirm what the wideband says. We can do a free air calibration but after that I'm lost.
A proper wide band is about 100 times more acurate than a calculated ratio.
This is actually pretty funny. The OP asked about differences between dyno and vehicle readings, and it has turned into a bashing of wide band sensors thread. When in reality, they are good enough for about every professional motorsport on the planet! :wink:

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 9:02 am
by BradH
Warp Speed wrote:
Wed Nov 01, 2017 9:28 pm
This is actually pretty funny. The OP asked about differences between dyno and vehicle readings, and it has turned into a bashing of wide band sensors thread. When in reality, they are good enough for about every professional motorsport on the planet! :wink:
I'm good; the things being discussed now are still of interest and should give me a better understanding of what to expect.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 11:40 am
by Tuner
Warp Speed wrote:
Wed Nov 01, 2017 9:28 pm
A proper wide band is about 100 times more acurate than a calculated ratio.
This is actually pretty funny. The OP asked about differences between dyno and vehicle readings, and it has turned into a bashing of wide band sensors thread. When in reality, they are good enough for about every professional motorsport on the planet! :wink:
It seems like there's always somebody who'll cry if he doesn't get what he thinks is sugar in every bite, even when he gets fed with a clean spoon.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 12:35 pm
by Warp Speed
Tuner wrote:
Thu Nov 02, 2017 11:40 am
Warp Speed wrote:
Wed Nov 01, 2017 9:28 pm
A proper wide band is about 100 times more acurate than a calculated ratio.
This is actually pretty funny. The OP asked about differences between dyno and vehicle readings, and it has turned into a bashing of wide band sensors thread. When in reality, they are good enough for about every professional motorsport on the planet! :wink:
It seems like there's always somebody who'll cry if he doesn't get what he thinks is sugar in every bite, even when he gets fed with a clean spoon.
Sure.......

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 12:45 pm
by RCJ
Advancing the timing will show leaner on a flow meter also.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 12:49 pm
by racear2865
when Im on my dyno, I live by the O2 sensor. When one gets whacky . I start looking for leaks. Yes I have EGT also. They are just another gage and mor data. You have to decide what you want to do with it. I also read spark plugs after every fire just to look for consistency. I do not care what other people say or think. I know what I look for and I know when Im in the ball park. With out all these data points, tell me how you know.
reed

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 1:03 pm
by CREngines
if you add timing and it shows leaner there is a very simple reason why.

You are burning more fuel in the chamber instead of it exiting into the header.

not all of the fuel magically disappears when the plug lights, in particular the unatomized parts.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 02, 2017 1:09 pm
by Tuner
More timing = more NOx ... :wink: ...