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I cruised throught the manual you reference and I see a table that compares AFR to lamba but not %CO. I may be missing what you saw in the manual, if so, please point me to it. I am hoping to see a table that compares specific AFR values to equivalent %CO values.

 

Thanks for the quick reply

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From the Megasquirt manual...

 

the products of combustion vary considerably with operating conditions, a multitude of design factors, and fueling/ignition strategies.

 

AFRemissions.gif

 

Rgrds

 

I have a couple of comparisons of AFR to %CO and they are not the same. Does anyone have a good comparison of AFR to %CO? Maybe in the range of 14.72 - 12.64 AFR.

 

Thank you

Bill,

 

CO and AFR are directly related and can be converted.  14.72 AFR equals 0.1% CO and 12.64 AFR equals 5.0% CO.  Outside of emission testing, you want a full load WOT AFR around 13.00 or 4.00 % CO for best output.  Best economy under load low cruise (<18% throttle) for an M10 occurs around 15 AFR with ignition advance well out into the 40's BTDC if you have programmable EFI.

 

Paul

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CD,

 

I run high 12s to low 13s at idle and at various throttle postions high 12s (12.6 - 12.8) to very low 14s (14.11 - 14.15). The plugs look ok.

 

To reference specific throttle postions and load:

 

Idle - High 12s to low 13s

 

Partial throttle while accerlating - 14.1 - 14.5

 

Running at consistant speed on level ground - mid 13s

 

WOT - 12.64

 

Overall when I peek at the gauge while driving under various loads, I seem to see 13s.

 

One could say it is a bit rich at idle and it goes a bit lean on partial throttle.

 

I do not think these are wild fluctuations and within a reasonable range. The new 02 sensors and gauges can really bounce around on these older cars making a consistant reading difficult.

 

I do see 15s on throttle lift off but I think that is consistant with how the Kugelfischer works.

 

The chart you posted for my, and the classes, benefit looks like the same chart Gunston provides.

 

Thanks for the responses class and more comments or discussion apprecitated.

 

I know we have been through this many times before so thanks for the indulgence.

Edited by BillWilliams
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COtoAFR-page-001.jpg

You should not expect to see one AFR all the time. At partial throttles it should go leaner. See these curves for AFR vs. throttle position (air consumption varies with throttle position) at constant RPM.

afrtoairflow.jpg

Byas

Edited by bnam
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Other than it being "nice to know" trivia, I don't see in today's world, what the value is of a %CO/AFR table.  That's old scool prior to the advent of the O2 sensor and would only be of usable on a dyno with an exhaust gas anaylzer in use.  And before the gas analyzers, an Orsat analysis was used to capture %CO.

Today that table is worthless because it is much easier and cheaper to use an O2 sensor than to do the exaust gas anaylsis routine.  It works for setting the idle with the gas analyzer and that's about all.

The table values are based on a specified fuel and can be arrived at by way of a combustion calculation if one knows the ultimate analysis of the fuel.  That table can't cope with oxygenated fuels either.

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Today that table is worthless because it is much easier and cheaper to use an O2 sensor than to do the exaust gas anaylsis routine.  It works for setting the idle with the gas analyzer and that's about all.

The table values are based on a specified fuel and can be arrived at by way of a combustion calculation if one knows the ultimate analysis of the fuel.  That table can't cope with oxygenated fuels either.

 

Good point.  I used it for setting idle CO% (as the specs called for that).  But, didn't consider the oxygenated fuel impact.

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Bill is there a specific questions with AFR to CO? As jimk said fuel chemestry is important so if you fill up the tank with E0 vs E20 you are going to see some changes. I don't know what you have out in MD but if it is available I would only put in E0. Just my 02 cents but with an old car with valuable engine parts (that is not a track rat) fat and happy is good as long as there was no smoke, drivability is good, and the plugs are clean.

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