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Stioch and WOT E85 AFR's?

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Don't worry about it your gauge only cares about Lambda, and is converting it to AFR assuming you are using gasoline. Stoich will still be Lambda 1, and will display as 14.7:1.


To convert to lambda divide the AFR by the stoich mixture for the fuel. In your case with a gasoline calibrated gauge, you would divide the reading by 14.7 to get your lambda value.



Fuel                      AFRst     FARst     Equivalence   Lambda
----                      -----     -----       Ratio       -----

Gasoline   stoich          14.7    0.068       1           1
Gasoline Max power rich    12.5    0.08        1.176       0.8503
Gasoline Max power lean    13.23   0.0755      1.111       0.900


E85 stoich                 9.765    0.01235    1          1
E85 Max power rich         6.975    0.1434     1.40       0.7143
E85 Max power lean         8.4687   0.118      1.153      0.8673


E100 stoich                9.0      0.111      1          1
E100 Max power rich        6.429    0.155      1.4        0.714
E100 Max power lean        7.8      0.128      1.15       0.870




On a boosted car, shoot for an AFR reading around 11.5:1 or a little richer, on E85 with a gasoline calibrated wide band at WOT and you will be good. Your idle AFR's on a gasoline calibrated wide band will still be about 14.7:1. Guys running boost like richer mixtures so will run all the way to Lambda .72 or so, which shows as a gasoline calibrated AFR of (0.72 x 14.7 = 10.58).


If you were naturally asperated you could run leaner, very near the 12.5:1 you would shoot for on gasoline.

On light boost you still can run leaner than 11.5 displayed AFR but don't get carried away trying to go too lean, there is a limit even on a fuel as good as E85.



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I have seen a couple of articles dealing with boost that claim max power was made at about .82 lambda or 12.0 AFR on a gasoline O2 sensor.  Although, the high 11's would definitely be on the safe side.  I try and shoot for 11.9-12 under boost right now, although I'm still working through all the base maps for E85 - and kind of working my way through while driving the car (ie drive to work, examine datalog and make corrections, drive home, log and make more corrections)  I really need to set aside a day or two and a couple tanks of gas to do it all at once!


When I get everything close, I'd like to hit the dyno for some fine tuning, but don't know if that will ever happen!

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