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.

 

[Tgscott]

I use non ethanol 90 and get almost 20 mpg on my 2010. It also runs better…

 

[swathdiver]

I use non ethanol 90 and get almost 20 mpg on my 2010. It also runs better…

I've run Rec90 by mistake, my wife, and the motor was knocking all over the place as soon as you gave it gas. Stuck it in 4th on the highway to burn 6 gallons and topped off with E85 and no more knocking.

Now let's respond to the OPs opening post:

Yes, Ethanol does run cleaner and does clean out a combustion chamber better than gasoline.

As for the disparity in range, it's not as much as most suggest in the GMT900 platform:

2009 GMC Yukon XL

2013 GMC Sierra CC with 6.2

Several years ago there appeared to be no standard in which we could ascertain the octane rating from an ethanol percentage. E85 itself was stated to be several different octane numbers.

What I did was use Sunoco's numbers for their race fuel, E85R. They state that the R+M octane rating for this fuel is 99 octane. We also know that E15 is listed as 88 octane. So I made a spreadsheet to figure the differences between the two numbers. Happy to share it.

Each percent between E15 and E85 is worth .15714 added to the octane rating.

Marky, I want to continue another discussion we had some time ago about fuel and oil and how it affects wear. Lake Speed Jr. came out with a video last month showing how using higher quality fuels result in less engine wear. I was amazed and it confirmed my own experiences. However, I'd love to see a comparison with E85 thrown into the mix. Does it have the anti-wear properties mixed in with the best top-tier fuels? I don't know.

 

[Fless]

Topped off the Red Hoe last week with E85 from 1/2 tank left of a prior tank of the same. Before filling up, the ethanol was 66%, and after fill-up it was 68%. My usual station typically pumps E69 all year long -- one of the reasons I go there, it's consistent. The station's elevation is just above 5,700 ft AMSL.

 

[swathdiver]

Topped off the Red Hoe last week with E85 from 1/2 tank left of a prior tank of the same. Before filling up, the ethanol was 66%, and after fill-up it was 68%. My usual station typically pumps E69 all year long -- one of the reasons I go there, it's consistent. The station's elevation is just above 5,700 ft AMSL.

Mine has been calculating 74% and have to see how the pickup is calculating the E85 from the same station. My Sunoco is 33 feet AMSL! LOL

Had to check google earth.

 

[Marky Dissod]

... let's respond to the OPs opening post ...

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

Each percent between E15 and E85, is worth .15714 added to the octane rating.

So, at sea level, about 30% E85 + about 70% 87 Octane ≈ 91 Octane?
How much more E85 does one need as altitude rises?

... want to continue another discussion we had some time ago about fuel and oil and how it affects wear.
Lake Speed Jr. came out with a video last month showing how using higher quality fuels result in less engine wear.
I was amazed, and it confirmed my own experiences. However, I'd love to see a comparison with E85 thrown into the mix.
Does it have the anti-wear properties mixed in with the best top-tier fuels? I don't know.

I'd be tickled pink to continue the discussion, but I'm at a loss as to how to contribute meaningfully, since I'm clueless as to how to quantify the relative amount of anti-wear additives in 'E85'.
Of special concern for me:
Does the anti-wear concentration vary with the ethanol concentration?

 

[swathdiver]

So, at sea level, about 30% E85 + about 70% 87 Octane ≈ 91 Octane?
How much more E85 does one need as altitude rises?I'd be tickled pink to continue the discussion, but I'm at a loss as to how to contribute meaningfully, since I'm clueless as to how to quantify the relative amount of anti-wear additives in 'E85'.
Of special concern for me:
Does the anti-wear concentration vary with the ethanol concentration?

I come up with 90 octane on my calculator, close enough for tv. As for how more for altitude? I have no idea.

About our previous discussion, you may be onto something but we'll have to wait and see if Lake Speed Jr. does any testing on E85.

 

[Marky Dissod]

I come up with 90 octane on my calculator, close enough for tv.

Although 90 octane should be covered by the Low Octane Spark Timing table, I pessimistically skewered all the numbers I used (E50, not E83), and came up with 91 octane, but at sea level.

... we'll have to wait and see if Lake Speed Jr. does any testing on E85.

Regarding anti-wear properties, yes indeed, we'd all love to see it.

 

[LSCALADE]

I use the 2:1 on my Escalade, I reference the screen that shows GAL Used, then lets say I need 18 GAL, I add 6.5Gal E85 and the rest 87 and I usually end up with E30-E35 ethanol, and with that I get about equal or better than 93 octane MPG. Powerwise they feel the same and I get zero Knock Retard.

If the ratio drops under E30 then periodically I get a stair stepped knock which actually likely is coming from a bad motor mount which will be addressed later.

Straight E85 I usually get 10-11mpg but no power issues at all.

 

[swathdiver]

I use the 2:1 on my Escalade, I reference the screen that shows GAL Used, then lets say I need 18 GAL, I add 6.5Gal E85 and the rest 87 and I usually end up with E30-E35 ethanol, and with that I get about equal or better than 93 octane MPG. Powerwise they feel the same and I get zero Knock Retard.

If the ratio drops under E30 then periodically I get a stair stepped knock which actually likely is coming from a bad motor mount which will be addressed later.

Straight E85 I usually get 10-11mpg but no power issues at all.

6.5 gallons of E85 @ 80% and 11.5 gallons of 87 @ 10% yields an alcohol content of about 53% and an octane rating of 90. This assumes the remaining fuel met the same mix as before, 24% alcohol content and 89 octane. Works!

 

[Mudsport96]

I think alot of my problems with the Tahoe and e85 is that it is an 06. It doesn't show percentage of alcohol in the appropriate PID. It just has a no/yes for high ethanol level.
And it just gets trash for mileage on anything other than regular or e15.
The power is there with straight e85, but anything between e15 and e85 i can get alot of knock retard if I lean on it to hard.
I had been thinking about adding a ethanol content sensor and reflashing the computer to an 05 OS, but the daughter is going to buy it off of me in a few months. And while I will still be working on it when she needs something. But, if I am not available and she has to take it somewhere, having the wrong pedal and TAC module and ecm software might cause issues.