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Remapping for pump fuel from e85

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Just finish building a mazda rx7 and the customer bought an AEM series 2 from a rx7 thats was tuned on e85 and using 2000cc injector

he is tight on funds . So question is how do i make the changes from e85 to pump. Do i use a overall fuel trim across the entire map or is there an easier way. i am told by different people i need to reduce fuel by 33% to bring it back to the range of pump fuel.

could someone shed some light

What injectors are you using now? If you are using different injectors you will need to change the injector setting in the software. Then, I would assume, if everything else is equal and the O2 output is set to Lambda and not AFR the ECU should adjust accordingly. Don't take my word on this as I have never used that type of ECU, so please wait for someone more knowledgeable to answer.

If the injectors are the same as the ECU was setup with you will need to adjust the fuel tables by approximately 33% because the required amount of E85 is proportionately higher than regular pump gas. Once you have done that you will still need to fine tune but it should get you close.

Don't forget to reduce timing advance as well if the previous car was optimized for E-85, since E-85 has a higher knock threshold.

That, or be fully honest and up-front with the customer in asking him to wait until he can afford a full tune to enjoy his car for years, not months.


Good point Pat. I should have remembered the octane -knock difference.

Andre done a good webinar on tuning for E85, if you take the principles explained and reverse engineer them you won't be far off, what I would say is try to get the customer to save for a full map as it could end up costing him more in the long run.


thanks alot guys .i have told the customer to hold till he could afford a whole tune . he has a link g4 for the rx7 but didnt bother to use it because the perivious tuner didnt like it . the link is a bit confusing but with the webinars i think i could manage

I wouldn't trim 33% as first step because the blend changes from station to others,summer absand winter,

slow down to get idea about what are you doing and what the car needs.

Pull timing and listen to knock. E85 is very different than pump gas not for just the octane rating,burn rate and combustion temp as well which reflects on the tune.

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