Question on Stoich vs. afr vs. Lambda

[8850]

I have a commanded Stoich of 14.08 in my file. If I want an afr of 11.3 then I should tune for a .80 Lambda?

2013 GT500 with factory installed widebands.

[murfie]

Lambda 1= stoich for all fuels. Afr stoich changes depending on the fuel you are running.

[jchambers]

Learn to forget AFR. Tune by lambda, now and forever. The base fuel at WOT is in lambda, the sensors are indicating lambda, calibrate so that the two match.

[murfie]

So lambda .8 for e10 is not the same afr for lambda .8 for e85. But both refer to lambda .8.

[8850]

Yes, I'm tuning in Lambda. My pump where I buy my fuel says up to 10% ethanol. Just want to be sure I'm reading my Lambda correctly based on afr. Most say 11.3 afr gives good safe power with this engine. Logging a .80 Lambda with my stoich of 14.08 and with the fuel I'm buying does that relate to a 11.3 afr? Thanks guys!

[murfie]

Lambda times a stoich afr= actual afr. .8 times 14.08= 11.26.

[8850]

Lambda times a stoich afr= actual afr. .8 times 14.08= 11.26.

So with my available fuel, my Stoich entry then if I log .80 lambda I'm at 11.26. Just want to be sure I'm at a safe fuel mixture but also making good power. My previous history has been with a tune file with Stoich at 14.68 or so, reason I'm concerned that I'm doing it correctly.

[murfie]

Yes lambda multiplied by stoich value will be commanded AFR. I said actual before but that would be what the sensor afr would be saying. Easiest way is set stoich value according to fuel you are running. Then less than 1 values are rich and greater than 1 values are lean in the logs.

[8850]

Yes lambda multiplied by stoich value will be commanded AFR. I said actual before but that would be what the sensor afr would be saying. Easiest way is set stoich value according to fuel you are running. Then less than 1 values are rich and greater than 1 values are lean in the logs.

Thanks again! I had a CTS-V prior to this car and I always tuned for about .77 Lambda. But it had a file Stoich of 14.68. To equal with this car now I need to tune for .80.

[Higgs Boson]

the issue here is that all wideband controllers/displays interpret Stoich AFR differently. They are all lambda 1 but some might display lambda 1 at 14.55 or 14.68 or 14.7, etc etc so then your afr will be off if you are chasing the wrong interpretation.

you need a wideband that works/displays in lambda or you need to ignore your wideband display and get the right transfer function in the Scanner for your wideband's lambda.

[murfie]

This is true if you have a external wide band. When changing it in the ecu the algorithms know what the factory wide band lambda is based off and uses the commanded stoich value to correct lambda in the ecu.

[Higgs Boson]

This is true if you have a external wide band. When changing it in the ecu the algorithms know what the factory wide band lambda is based off and uses the commanded stoich value to correct lambda in the ecu.

good point, I forgot which subsection i was in. ;-)

[8850]

good point, I forgot which subsection i was in. ;-)

Yes, my 2013 GT500 has factory widebands.