A/F ratio vs Lambda reading

[hobieboy]

Hi,
Just wonder if anyone knows the formula for converting lambda readings to A/F ratio?

For example, 14.7:1 seems to be the good A/F ratio, while lambda of 0.98, I believe, is the equivalent "good" reading. But how do they correlate?

thanks.

[Bill Verburg]

14.7 is stoichiometric or theoretically ideal for complete combustion

l = (Induction Air Mass)/(Air Requirement for Stoichiometric Combustion)

l = 1 Stoichiometric Combustion
l < 1 Air deficiency, i.e. Rich mixture, max. power @ l = 0.85 &#133 0.95
l > 1 Air excess, i.e. Lean mixture, min. fuel consumption & reduced performance @ l = 1.05 &#133 1.3
l > 1.3 The mixture ceases to be ignitable, Ignition miss occurs, accompanied by pronounced loss of operating smoothness.

[hobieboy]

Hi Bill,

Thanks for the explanation - very much in line with my understanding of how to interpret lambda value & A/F ratio.

What I was trying to correlate is how to convert a lambda value of say .80 to A/F ratio.

One of the problems I'm chasing is that on 1 wide band O2 sensor, it shows that I'm running way rich on full boost (0.78), but on a dyno with a different wideband, it shows that I'm running 13.0 A/F - way lean. So, I'm interested in seeing if I can somehow convert these readings into the same unit value for better comparison.

[hobieboy]

Hi Noah,
I'm in fact consider getting the LM-1 as well Sounds like you have nothing but positive experience with it?
One question on that unit - did you also get the extended cable between the unit & O2 sensor or is that something I can make? (Don't think the standard 10' is enough to get from the exhaust to the front seats).
thanks

[joeclarke]

"Lambda" simply expresses a function of "stoic" - 14.7 AFR. In other words 14.7=Lambda 1.0. Hence Lambda .78 = 11.47 AFR (14.7 X .78).

Pretty rich there big fella...

[Purrybonker]

Patrick - I have an LM-1 as well. I've used it to set up most of my "fleet" and am currently using it to work with Steve Wong on fine tuning my MAF and AFM chips. The LM-1 has certainly shown me that custom tuning a chip to each individual engine is the way to go.

The LM-1 makes the process of gathering AFR data under all load conditions pretty simple.

The line on the O2 is plenty long for any vehicle that comes to my mind (with the possible exception of a winnebago) - I've even used it on my long box pick-up truck and station wagon with no particular problems. Don't forget that you're using the O2 bung on a cat vehicle - tail pipe or bung on a non-cat. But if line length was an issue - I don't see a problem in making up an extension with components from Radio Shack.

BTW Patrick - I will probably be selling my LM-1 (with all the handy peripherals) in the next few weeks. Once I've set up all my vehicles (even the lawn mower, outboard and tiller) - I'll probably let it go. Maybe we can hammer out a made-in-Canada deal...

[hobieboy]

Hi Purrybonker,
Thanks for the info... certainly interested in working out a made-in-Canada deal Cross border duty/shipping is just a murder. However, I do need to get my A/F issue sort out ASAP so depending on your timing.
Do you mind PM me for details?

[Bill Verburg]

joeclarke, put more clearly than I did
AFR = 14.7 x l

[Purrybonker]

Originally posted by PatrickT
Hi Purrybonker,
Thanks for the info... certainly interested in working out a made-in-Canada deal Cross border duty/shipping is just a murder. However, I do need to get my A/F issue sort out ASAP so depending on your timing.
Do you mind PM me for details?

Yeah Patrick - you've got your PM turned off. But I can tell you that I'm probably a week away at best - maybe longer if I need further chip iterations.

[aigel]

That unit rocks. And yes, the cable that comes with it is plenty long. I have run it through the inside of the fender, at the door sill and then into the cab and had cable left ...

George

[ttweed]

Originally posted by PatrickT
One of the problems I'm chasing is that on 1 wide band O2 sensor, it shows that I'm running way rich on full boost (0.78), but on a dyno with a different wideband, it shows that I'm running 13.0 A/F - way lean.

Is this a typo? 13.0 A/F ratio is in fact a richer mixture than Stoich. 15.0 would be lean.

TT

[sammyg2]

Go here:
http://hp.autometer.com/techtips/faq_tech_writeups/air_fuel/air_fuel.html
They have the standard stoich curve with voltage on the left and ratio on the bottom.
That should answer your questions.


Yes, 13 is richer that 15 to one.

A/F is a ratio of air to fuel (by weight, not volume) so the lower the number the less air compared to fuel, so it is more rich.

[hobieboy]

Yes - 13.0:1 is indeed richer than Stoich.

Unfortunately 80 vintage turbo motors likes to run at about 11.5:1 on full boost based on all the expert knowledge I have gathered so far (thanks to CIS). Anything above 12.5:1 will risk blowing holes in the piston.

In my case, the car is used mainly on track; ie. with extended boost period, hence I do need to fix that before I blow anything.

Purrybonker - you have PM

[Steve W]

Here you go -

Lambda AFR
0.686 10.08
0.696 10.23
0.706 10.38
0.716 10.53
0.727 10.69
0.739 10.86
0.750 11.03
0.762 11.20
0.774 11.38
0.787 11.57
0.800 11.76
0.814 11.96
0.828 12.17
0.842 12.38
0.857 12.60
0.873 12.83
0.889 13.07
0.905 13.31
0.923 13.57
0.941 13.84
0.960 14.11
0.980 14.40
1.000 14.70
1.037 15.25
1.078 15.84
1.121 16.48
1.169 17.18
1.220 17.93
1.276 18.76
1.337 19.66
1.405 20.66

[joeclarke]

Originally posted by Purrybonker
Patrick - I have an LM-1 as well. I've used it to set up most of my "fleet" and am currently using it to work with Steve Wong on fine tuning my MAF and AFM chips. The LM-1 has certainly shown me that custom tuning a chip to each individual engine is the way to go.

The LM-1 makes the process of gathering AFR data under all load conditions pretty simple.

The line on the O2 is plenty long for any vehicle that comes to my mind (with the possible exception of a winnebago) - I've even used it on my long box pick-up truck and station wagon with no particular problems. Don't forget that you're using the O2 bung on a cat vehicle - tail pipe or bung on a non-cat. But if line length was an issue - I don't see a problem in making up an extension with components from Radio Shack.

BTW Patrick - I will probably be selling my LM-1 (with all the handy peripherals) in the next few weeks. Once I've set up all my vehicles (even the lawn mower, outboard and tiller) - I'll probably let it go. Maybe we can hammer out a made-in-Canada deal...

I've been known to pop up in Calgary once in a while - let me know when you're ready to sell...

[sammyg2]

I have mine set up for around 12.5 to one under boost, but I'm only running 1/2 bar boost (with stock 1980 SC compression).

[hobieboy]

Sam, I was seeing my A/F goes lean starting from 4,500 rpm and hit 12.7 by the time I hit 5,600 rpm. So you can interpolate where it would be at 6,500 rpm

I'm running ~.9 bar of boost using a .6 bar spring.

[klatinn]

Hi,

To simplify AFR/EFI tuning with the LM-1, you can use the following procedure:

1. Gather AFR data under all load conditions and RPMs. Use long logs without a lot of throttle blips and transitions to increase data reliability. If your ECU is MAF based, use RPM and MAF voltage. If speed-density based, use MAP and RPM and so on.

2. Set up the 3D chart in LogWorks to match the main fuel chart of your ECU (RPM/Load spacing). Set it to calculate the chart over all sessions in the log to minimize deviation.

3. Save the 3D chart as .dif file and load it into Excel.

4. In the spreadsheet, enter the target AFRs in a second table under the measured (and loaded) AFR table.

5. Enter the fueling table settings from your current ECU table in a third table under the second table. Units don't matter as long as a higher number means more fuel.

6. Create a fourth table under the third one. This table has in every field the formula:
ECU-table-value * current-AFR-value / target-AFR-value for each field.

This table shows now the new fueling table for your ECU. It should produce AFR's close to your target.

Regards,
Klaus

[klatinn]

I forgot to mention:

In case the sensor cable is really too short for some applications you can temporarily extend it with a keyboard extender cable (6 ft) from the computer store. Older PC's had the same DIN-5 connector. They work for extending the LM-1 cable (at least the ones I tried). Don't go longer than that without shortening the power cable by the same amount though.

Regards,
Klaus

[Purrybonker]

Joe Clarke you have PM

Patrick - you have more PMs than you really need.