Different Blends

da2k17

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i Have a few questions on tuning with the different blends of ethanol.

the true e85 is only available in the summer for a short period of time for what i read (northern half of PA), so for fall and spring its e70.

what is the difference in octane between the two different blends?

how is tuning affected when going from one to the other? i read you can go from e70 to e85 with no issue but not the other way around, is that correct? why?

thats it for now, im sure ill have some follow ups. also i dont a want guess, if you dont know please dont answer.
thanks
:beer:
 
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TRQJUNKIE

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id try and get some e85 in 55 gal drums and store if its just for a race tune but if your running an e85 tune all the time then that would be a lot to store haha.
 

RFH

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The octane of gasoline/ethanol blends is non-linear. It increases 3 points at E10 and at E50 the octane is around 100 and levels out after that.

Each 10% in ethanol added to gasoline will require an additional 3% of extra fuel due to the increased oxygen concentration in the ethanol (which is ~28% oxygen by mass). So a tune for E70 will be 4.5% leaner than a tune for E85.

Basically an E70 tune would be lean running E85 and an E85 tune will be rich running E70.
 

da2k17

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The octane of gasoline/ethanol blends is non-linear. It increases 3 points at E10 and at E50 the octane is around 100 and levels out after that.

Each 10% in ethanol added to gasoline will require an additional 3% of extra fuel due to the increased oxygen concentration in the ethanol (which is ~28% oxygen by mass). So a tune for E70 will be 4.5% leaner than a tune for E85.

Basically an E70 tune would be lean running E85 and an E85 tune will be rich running E70.

that was exactly what i was looking for, thanks.

how is everyone compensating for variances? i know about testing each time you fill up up, so what are you guys doing when you run into a difference with what you have compared to what you were tuned with? can i simply reduce timing on my sct xcal3 if i find im running a higher concentration than i was tuned for?
 
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04sleeper

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It doesn't really matter on tuning between E70 and E85 honestly. E85 has a much larger "Sweet Spot" when tuning A/F than gasoline. If you tune for E85 at 12:0 A/F (on a gasoline scale), it will just go a little rich when running E70. It will make basically the same exact power. If you tune for Mid 11's on E70, you will still be fine on E85.

Better to just tune using Lambda. Between .7855 for E70 to .8197 for E85.
 

da2k17

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the thing that has me worried is that there is only one station 40 miles away that has ethanol. if 85 is only available for a short time and not a lot a people use it who knows how long it will be before they get another tank full, the station may never even have true e 85.

so i guess if i just tune the e70 a little rich it will lean up if i have a higher blend closer to e85. guess the most important thing is to always check the percentage. thanks for the input.
 

BruceH

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that was exactly what i was looking for, thanks.

how is everyone compensating for variances? i know about testing each time you fill up up, so what are you guys doing when you run into a difference with what you have compared to what you were tuned with? can i simply reduce timing on my sct xcal3 if i find im running a higher concentration than i was tuned for?

I test mine. So far it's gone from 80% to 75%. For both I'm running a stoich of 10.2 vs 85% 9.9. I watch my trims all the time and the recent batch of 75% hasn't affected them much at all.

Like mentioned in a previous post there is alot of forgiveness with e85. If I ever get some true 85% I'll just load the 9.9 tune that's already on my x3 waiting for the occasion.

I'm going to run the 75% on the dyno next month. It will be interesting to see how much if any difference it makes.
 

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