87 and E85?

[mycbtech]

So this is definitely going to sound like a noob question but I can't seem to really find a direct answer. I'm currently running e50 and do my mixing of 91 and e85 to get to the e50 mix. But being in california, 91 is so expensive whereas 87 is anywhere between 40 to 75 cents cheaper. It seems to me, that I should still be able to get the same ethanol mix by mixing 87 and e85 to get to the e50 mark. Is that plausible or would I be running way too much e85 and have a possibility of thinning the fuel out too much?

 

[WFO-TSi]

It is possible to get to 50% Ethanol while blending "E85" and 87 octane fuel. Your question leads me to believe that you aren't actually measuring the "E85" coming out of the pump...If you aren't you should be.

I've seen Ethanol content for "E85" anywhere between 52-89% depending on season and location.

 

[bstkoehler21]

It is possible to get to 50% Ethanol while blending "E85" and 87 octane fuel. Your question leads me to believe that you aren't actually measuring the "E85" coming out of the pump...If you aren't you should be.

I've seen Ethanol content for "E85" anywhere between 52-89% depending on season and location.

His question is regarding octane, but you raise a valid point; OP should be measuring the ethanol content of his e85 for proper calculation and consistency. To maybe rephrase what he's asking - All other things constant (ie. 87/91 octane 10%ETOH or 87/91 octane 0%ETOH, AND true E85 gas), will you notice a difference using 87 octane vs 91 octane when blending to e50? Obviously, you would need less e85 if your 87/91 option is 10%ethanol vs no ethanol.

I also am curious to hear opinions or see data. I want to start upgrading; but to echo past posts/comments, these motors seem to love ethanol. Still completely stock, but I can attest to that, noticing increased power/response when using 10%ETOH, but mileage decreases.

I'd also welcome comments or opposing views, but my overall takeaway, being completely stock (unfortunately), is -- increase octane -> increase milage, increase ethanol -> increase power/decrease mileage. Trying to remain as objective as possible, I believe my ST runs/drives the best on 93 octane w/10% ethanol. Now, if I were to be doing a long road trip and wanted to get the most miles/tank, 91 octane 0% ethanol would achieve best results. As always, your miles may vary.

 

[WFO-TSi]

My apologies, I didn't see the DIY Ethanol Sensor listed in mycbtech's mods. If your concerns are a reduction in overall octane, then please see below:

Check out the attached file to see calculated octane values for Ethanol blends with premium.

The chart shows a true 50% E mixture with 91 octane pump gas having, effectively a rating of 101 octane.

This .GOV link shows Ethanol having an octane rating of 109.

Selecting the Right Octane Fuel (fueleconomy.gov)

Using an online fuel blend calculator and using the values for E listed above and then 87 for the gasoline I get a rating of 98 octane for a 87 based 50% E blend. That assuming that the 87 octane fuel didn't have Ethanol in it (which it almost always does) so the overall value will be slightly lower.

@mycbtech, I don't have any firsthand experience with that blend but doing a before and after datalog and seeing how much "Knock Octane Modifier" drifts or the "Air Load" values drop will give you an idea of what power is lost with the change in overall octane.

 

[mycbtech]

My apologies, I didn't see the DIY Ethanol Sensor listed in mycbtech's mods. If your concerns are a reduction in overall octane, then please see below:

Check out the attached file to see calculated octane values for Ethanol blends with premium.

The chart shows a true 50% E mixture with 91 octane pump gas having, effectively a rating of 101 octane.

This .GOV link shows Ethanol having an octane rating of 109.

Selecting the Right Octane Fuel (fueleconomy.gov)

Using an online fuel blend calculator and using the values for E listed above and then 87 for the gasoline I get a rating of 98 octane for a 87 based 50% E blend. That assuming that the 87 octane fuel didn't have Ethanol in it (which it almost always does) so the overall value will be slightly lower.

@mycbtech, I don't have any firsthand experience with that blend but doing a before and after datalog and seeing how much "Knock Octane Modifier" drifts or the "Air Load" values drop will give you an idea of what power is lost with the change in overall octane.

thanks for the Reply. for all intents and purposes it looks like it would end up being the same mix you would just need more E85. I was able to get the blend I wanted from using 87 over 91 and honestly, it didnt save me that much money lol. blending to get e50 on an empty tank takes about 6 gallons of 87 so I saved around $2.40 when all was said and done.