Adding ethanol to raise octane ...

[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.