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how to tune air ratio

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How do you tune car running on e85 do you set your air ratio lower


The stoichiometric ratio for E85 by mass is 9.85:1.

The 'correct' technique if you wish to use units of AFR, would be to adjust the stoichiometric AFR setting for your wideband to 9.8:1. That being said I'm guessing that 99% of tuners in the world don't do this and leave the wideband stoich setting at 14.7:1 (pump gas). While not technically correct, you can tune like this but it will have a massive affect on your target AFRs.

Here's what I mean:

Let's assume you are tuning a turbo car on pump gas and you're aiming for 11.5:1 under boost.

Now let's say your wideband stoich is still set to 14.7:1 and you switch to E85. Despite changing the fuel, you would still target 11.5:1 on E85

If however you changed the stoich setting to 9.8:1 when you switched fuels, you would now be shooting for 7.7:1 AFR.

The easiest way to ensure accuracy, eliminate confusion and prevent any possible mistakes is to learn to tune in units of lambda. Lambda is a measurement relative to the stoichiometric AFR of the particular fuel. In the case above, 11.5:1 on pump gas would be lambda 0.78 (11.5 / 14.7 = 0.78). Likewise 7.7:1 on E85 is still 0.78 lambda (7.7 / 9.8 = 0.78).

Funny you say that Andre - it was 2 weekends ago I changed my maps air to fuel readout form AFR to Lambda...the next big change will be going from fahrenheit degrees to celsius degrees...baby steps!

Welcome back from the dark ages bealljk ;)

I must admit that while I can automatically decipher most imperial units without needing to think about them, I've never been able to get my head around fahrenheit. It just doesn't make sense to my little brain :(

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