Octane Rating of E-70? Winter Blend?

evane · Dec 3, 2008, 09:52 AM

I have been thinking about switching to E-85 and wondering if it would be best to tune to E-70, the winter blend to be safe. Because if you have a E-70 tune your never going to have to worry about a lesser blend of ethanol...but then I was thinking about the octane rating? what would the octane of it be? so i did some math...

My calculations are based on that E85 is 106 octane and 15% 87 octane gas and the other 85% is ethanol....

E-85 = 106 Octane

15% 87 Octane Gasoline and 85% Ethanol but whats the octane rating?

so i did my math...

15% of 87 Octane Gasoline is 13.05 Octane...

Thats leaves us with, 106 - 13.05 = 92.95 Octane but what's the octane rating of the pure ethanol?

85% of "?" = 92.95 Octane, Answer is.... 109.3529412 Octane

so E-85 is 15% 87 Octane Gasoline and 85% 109.353 Octane Ethanol

But! What is the octane rating of E-70?

30% 87 Octane Gasoline is 26.1 and 70% of the 109.353 Octane Ethanol is 76.54705884....

then....take 26.1 Octane + 76.54705884 = 102.6470588 Octane

E-70s Octane Rating 102-103 Octane....

Now these numbers are base on that the 15% of E-85 is 87 Octane Gasoline....I'm not sure what the octane rating of the gas is that they use and it might vary from state to state...

What do you guys think?

Jim in Tucson · Dec 3, 2008, 12:30 PM

Straight ethanol is 113 octane.

E85 is about 105 octane.

E75 is approx. 100 octane.

I found the above with a quick Google search on Al Gore's Internet.

I'd guess E70 to be about 98-99 octane, maybe 98.5.

03whitegsr · Dec 3, 2008, 12:58 PM

FWIW, we get E70 year roundin Utah and people have had no problem making huge power on it around here. I wouldn't worry too much about how aggressive you are on the tune. The only issue I see is just dealing with the different stochiometric AFR on the two different blends.

evane · Dec 3, 2008, 07:38 PM

98 octane is still alot better than 91 and thats what i'm tuned on is 91

JohnBradley · Dec 3, 2008, 08:17 PM

I am not sure that E98 is only 113.

The rating at the pumps here say it is no less than E70

and

The octane rating is no less than 105

It would leave me to believe E70 is 105 which is consistent with Rocket Fuel E85 being 112 (although this could be mixed up I admit) and the rumors I hear that paint E98 at 120.

I could be totally wrong about the octane...but I do know of an E98 9:1 car running 47psi from a 4202 with very little noise from the knock sensor (AEM car). It did this all season long without an engine failure.

Jim in Tucson · Dec 3, 2008, 08:17 PM

I gained 75 whp and 132 ft lbs going from 91 to E85. My parts selection was all made with maximizing torque as my primary focus. E85 really woke up my VIII. You will be extremely pleased with the results.

Here is my 91 tune (21psi) overlaid with the E85 tune (28psi).

JohnBradley · Dec 3, 2008, 08:22 PM

Interesting wiki FWIW:

http://en.wikipedia.org/wiki/Octane_...rement_methods

about 3/4 of the way through

Of course we are also talking about MON (minimum octane number) and not R+M/2 which would be Research Octane number (apparently RON is listed at 129 for pure ethanol, and 116 MON) + MON divided by 2. We are adding 87 octane (we assume) which is 87 R+M/2 so somewhere the math slipped up for what E85 is actually. For it to be accurate it needs to be the R+M/2 of Ethanol calculated with the R+M/2 of 87 octane at 85/15% concentration.

JohnBradley · Dec 3, 2008, 08:40 PM

For purposes of this post "r+m/2" will be refered to as the pump rating since we only have MON at the pump now and not the pump rating like we do with "pump" gas.

129 RON + 116 MON / 2 = 122.5 Pump rating for pure ethanol alcohol

122.5 r+m/2 @ 85% + 87 r+m/2 @ 15% (or 8.5 gallons to 1.5 gallons) would be 117.17 r+m/2 for E85. Now switching this to E70 (or 7g and 3g) would drop this (using the same values) to 111.85 r+m/2.

This assumes that the RON and MON ratings provided by that Wiki are correct, or the ones given that say 113 are incorrect.

Here is the blending calculator when we get some repeatable numbers:

http://www.ranney.com/mjr/fuel_blend.html

Simply enter 10 gallon tank, beginning octane, race octane, then BS dollar amounts since we arent interested in cost in this discussion so much. and then examine the chart at the mix ratio you are interested in.

03whitegsr · Dec 4, 2008, 09:06 AM

Quote:

Originally Posted by JohnBradley

I could be totally wrong about the octane...but I do know of an E98 9:1 car running 47psi from a 4202 with very little noise from the knock sensor (AEM car). It did this all season long without an engine failure.

Yep, +1 here coworker made over 700 WHP on his celica on E70 and a local 1G DSMer on E70 broke 700 WHP and went 10.1X and mid 140s. A local Supra GS300 guy just broke 900 WHP on E70 as well.

Making power on E70 doesn't seem to be an issue, regardless of what the octane number is.