Adding ethanol to raise octane ...

[Marky Dissod]

Note: this thread is NOT about whether or not you/anyone should buy E85 based on price vs range.
Short answer to that question is: if ethanol price is 74% of gasoline price or less,
DEFINITELY buy E85, because ethanol's drop in range is about 25%.

No one has yet quantified how much cleaner ethanol burns vs petrol (less carbon buildup),
and only you can quantify things like smiles per gallon for yourself.

However, what CAN be quantified, is the minimum amount of ethanol needed to raise 87 octane petrol to 91 octane ...

Assuming MINIMUMS of 50% ethanol E85 in winter @ 99 octane
Tahoes with 26 gallon tanks need to add 8.56 gallons of 'E85' to 17.44 gallons of 87 octane gasoline, for a 91.0 octane tank.
Suburbans w/ 31 gal tanks need to add 10.21 gallons of 'E85' to 20.79 gallons of 87 octane gasoline, for a 91.0 octane tank.

https://morepowertuning.com/pages/emix

then scroll down to the advanced calculator.

 

[B-train]

I have found that a 20 to 30% blend of E85 and 87 yields many smiles per gallon. My 2008 Denali loves it. At the summer octane of 105, I usually end up with 93-ish octane on that ratio and it works great.

 

[Fless]

@swathdiver does some kind of E85 mix to 'up' the octane. Maybe he can share some numbers with us.

 

[Marky Dissod]

@swathdiver does some kind of E85 mix to 'up' the octane. Maybe he can share some numbers with us.

Math has already been done for y'all.
Tahoes: at most 8.56 gallons of 'E85' + 17.44 gallons of 87 = 26 gallons of 91 octane.
Suburbans: at most 10.21 gal of 'E85' + 20.79 gal of 87 = 31 gal of 91 octane.

Another way to put it, for any other vehicle:
If 32.9% (or more) of your tank is E85 - even if it's only 51% ethanol because it's wintertime! -
your tank is (at least) 91 octane (if not higher).

 

[Fless]

Our winter E85 tends to be right at E69 -- at least where I get mine -- so our math here will be a bit different. Our low fuel is 85 octane; high altitude.

 

[Marky Dissod]

https://morepowertuning.com/pages/emix

The basic one on top of the page is pretty weak.
Scroll down to the advanced calculator.
It lets you tweak octane and ethanol %age of BOTH fuels.

Looks like you need at least 42.5% 'E85', Fless.

 

[Fless]

https://morepowertuning.com/pages/emix

The basic one on top of the page is pretty weak.
Scroll down to the advanced calculator.
It lets you tweak octane and ethanol %age of BOTH fuels.

Looks like you need at least 42.5% 'E85', Fless.

As long as I have my E85 source I'll just run it full strength.

 

[Mudsport96]

The problem (around my area anyway) is consistency of ethanol percentage in e85. It gets blended at the station. The truck drivers calculate the empty space of the in ground tank that needs filled. Then puts in 87 octane and fills with e98 to get the mix close to e85. So depending how accurate the tank levels are monitored, you could be wildly off your ethanol percent. That is why when I used to race using e85, I bought it by the drum and used that.

 

[Marky Dissod]

The problem (around my area anyway) is consistency of ethanol percentage in e85.
It gets blended at the station. The truck drivers calculate the empty space of the in ground tank that needs filled.
Then puts in 87 octane and fills with e98 to get the mix close to e85.
So depending how accurate the tank levels are monitored, you could be wildly off your ethanol percent.
That is why when I used to race using e85, I bought it by the drum and used that.

PLEASE re-read my previous posts - I ALREADY accounted for several variables with carefully considered pessimistic offsets.
I gave Fless a personalized answer because I failed to account for high altitudes.
Either feel free to check my maths, or click the link and scroll down to the advanced calculator (ignore the first calculator, it's weak@$$).

Pretty comfy stating that if most sealevel people use
2 parts 87 octane to 1 part E85 (regardless of time of year),
the resultant mix will be AT LEAST 91 octane if not HIGHER.