E85 vs 104 Octane- What am I missing here

[AllroadCorbin]

I've been running APR software on my B8.5 allroad for the last 3 years or so and its been fun. But the more I research into E85, the more confused and mildly concerned I get. So hear me out:

If you troll the interwebzz you will see varying opinions on E85. Youll find research and articles claiming it to have an octane of nearly 110. Some even say 116. Some say 108. But the most recent research I've been reading indicates that most pump Ethanol is barely higher than 94 (R+M)/2. Ethanol is not a very well controlled fuel and true ethanol content varies between 55% and 75% most of the time. I have conducted my own tests at local Boston stations and have found Ethanol content as low as 45% and the max I have ever seen was just shy of 80% in the summer.

If i'm not mistaken, the way that APR calibrates their software to make more power on E85 is by timing advance due the higher effective octane rating of Ethanol. Our flex fuel cars have a ethanol sensor that determines the % ethanol present in our fuel. My over simplified guess is that APR uses this device and has mapped out just how much timing advance their software can apply based on a given %ethanol readout from the sensor. This seems pretty straightforward. APR also tells us that the highest output they measured in testing came from running E85.... noticeably higher than running GT260 plus (104 octane)...I'm specifically referring to the B8.5 K04 files that I run. Our cars don't have an "Octane" sensor which is why if you put 100 octane in a car running a 93 file, it doesn't do jack shit. Same for when you put premium fuel in a ford haha.... not calibrated for it.

Now here is what confuses and worries me. The purest E85 you can buy comes in drums from Sunoco and has an (R+M)/2 of 99 octane. (R+M)/2 is how we commonly measure gas octane here in the states (anti-knock index). It's just a simple average of research and motor octane ratings. I have also found that the E85 I purchase at a local Gulf Station claims the fuel has a (R+M)/2 of 94 octane. So my questions then are as follows:

1. What factors does APR use besides timing advance (based on an octane assumption) to make E85 their highest output fuel given that pump E85 does NOT have a higher octane rating than GT260 Plus or even GT260.
A. What is the assumed (R+M)/2 that APR uses to calibrate for E85 use?

2. If APR is assuming those 110 octane figures from years past that have been proven to be false, then have they then created calibration that is actually using too much timing advance? Calibrated for an effective octane of 110 or something when the best we actually get is around 94? In the past I noticed some serious timing retard under heavy load using my APR mobile dongle and I'm wondering if this had something to do with it.

Hope this makes sense to yall and I would love somebody from APR to chime in and explain this to me, because if my logic and research is true, then I don't understand why a 104 octane file makes less power than when the car senses a full tank of pump E85.


Thanks,

Corbin

[adamazing]

The E85 I buy is always 70%. I think it's dipped to 69% just once.
The octane rating for pure ethanol should be between 113 and 115. If you take the conservative figure (113) and dilute it with 87 Octane (which I only assume since it's the cheapest pump fuel available), you get an Octane rating of 100.

But, that's not a 50/50 dilution mix, it's only 30%.
There is a 26 point octane rating difference between 113 and 87. 30% of that difference is 8 octane points.

113 (Ethanol) minus 8 Octane points (a 30% 87 Octane dilution) = 105 Octane.


I suppose the key factor is always going to be the E85 blend, and that's always going to be different from region to region, along with the seasons.

[AllroadCorbin]

The E85 I buy is always 70%. I think it's dipped to 69% just once.
The octane rating for pure ethanol should be between 113 and 115. If you take the conservative figure (113) and dilute it with 87 Octane (which I only assume since it's the cheapest pump fuel available), you get an Octane rating of 100.

But, that's not a 50/50 dilution mix, it's only 30%.
There is a 26 point octane rating difference between 113 and 87. 30% of that difference is 8 octane points.

113 (Ethanol) minus 8 Octane points (a 30% 87 Octane dilution) = 105 Octane.


I suppose the key factor is always going to be the E85 blend, and that's always going to be different from region to region, along with the seasons.

PURE Ethanol has an (R+M)/2 of 109. Pure E85 (which has a 15% mixture of gasoline) has an (R+M)/2 of 99. So no matte you and I do, the highest octane rating in our tank using a pure race E85 ordered from Sunoco is 99 (R+M)/2. What I'm wondering is what (R+M)/2 value APR has assumed. Previous research when this corn shit came out claimed it to be well over 110. Some even said 116 which is totally not true. IF that was true, then APRs E85 claimed hp/tq figures would make sense... but given what we now now about the true octane value of E85, it doesn't, and I'm concerned that its over-advanced and can damaged the vehicle over time. Ive logged a lot of big timing retard in the past using E85 and this would explain why. We have an ethanol sensor which changes timing based on a given % of ethanol in the tank, but if the assigned (R+M)/2 variable value in that timing calculation equation in their software is incorrect or too high, then we have a problem....since our cars don't sense "Octane"


Maybe i'm thinking about this all wrong but right now, it doesn't make sense

[hyperunion]

Hmmm very interesting study... And this could be a reason why giac decided to have a completely different switchable program for race gas and e85 and 93....
Tho people have been dynoing over the apr hp and torque figures that were stated...
But is the timing that is used for more hp calibrated for a specific octane or Ethanol percentage... ??.
Timing for a supposedly 105 octane when in reality your e85 may be only 95 octane could spell trouble...
Even more so with a k04 turbo running more boost..


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[energy_legs]

One of the reasons why more power can be made on E85 over something like race gas is because of the oxygenation of the fuel. In the most basic chemical sense, alcohols (in this case ethanol) have an oxygen atom in the molecule (-OH); because of this the fuel brings extra oxygen to the combustion reaction. The higher the content of ethanol in your blend the more oxygen is being added to the combustion chamber. The contributor to extra power does have to do with timing, ethanol has a more favorable latent heat than gasoline AND because you have to add approximately 30% extra fuel you have more adiabatic cooling.

The way the flex fuel stuff is calibrated is based on measured knock and scaled according to testing at multiple ethanol content percentages, not some octane calculation.

Just my $0.02 based on my understanding. Hope that helps steer your research.

[hyperunion]

One of the reasons why more power can be made on E85 over something like race gas is because of the oxygenation of the fuel. In the most basic chemical sense, alcohols (in this case ethanol) have an oxygen atom in the molecule (-OH); because of this the fuel brings extra oxygen to the combustion reaction. The higher the content of ethanol in your blend the more oxygen is being added to the combustion chamber. The contributor to extra power does have to do with timing, ethanol has a more favorable latent heat than gasoline AND because you have to add approximately 30% extra fuel you have more adiabatic cooling.

The way the flex fuel stuff is calibrated is based on measured knock and scaled according to testing at multiple ethanol content percentages, not some octane calculation.

Just my $0.02 based on my understanding. Hope that helps steer your research.

Hence why apr's method of blending maps to ethanol percentage may be superior as opposed to switching to a dedicated e85 file...

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[AllroadCorbin]

One of the reasons why more power can be made on E85 over something like race gas is because of the oxygenation of the fuel. In the most basic chemical sense, alcohols (in this case ethanol) have an oxygen atom in the molecule (-OH); because of this the fuel brings extra oxygen to the combustion reaction. The higher the content of ethanol in your blend the more oxygen is being added to the combustion chamber. The contributor to extra power does have to do with timing, ethanol has a more favorable latent heat than gasoline AND because you have to add approximately 30% extra fuel you have more adiabatic cooling.

The way the flex fuel stuff is calibrated is based on measured knock and scaled according to testing at multiple ethanol content percentages, not some octane calculation.

Just my $0.02 based on my understanding. Hope that helps steer your research.

Didn't know about the oxygen aspect but yes I understand the knock testing aspect... that's how (R+M)/2 values are assigned to gasolines you can buy at the pump. So you're saying that APR pulled a motor and did knock tests on every possible permutation of percentages? I would find that hard to believe but I hope I'm wrong. Either way, the (R+M)/2 of Pure E85 being 99 and pump E85 being 94 ish, this still doesn't help me understand how E85 supposedly cranks out more than 104 Octane if timing is the main factor in extra power production in E85 vs 93.

[AllroadCorbin]

Hence why apr's method of blending maps to ethanol percentage may be superior as opposed to switching to a dedicated e85 file...

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Right- In theory that's great but the car still can't read octane. It can read ethanol %. The (R+M/2) value of Ethanol must be predefined in the software for it to assign a timing value based on observed content right? See what I'm saying here?

As far as octane goes the car can only pull timing when it senses pre-det...which might explain some of the issues myself and others have had in the past

[Townending]

If what I've read is correct, the exhaust gas temp on E85 is several hundred degrees lower than gasoline (1200 vs 1500 IIRC). Due to lower exhaust gas temps, we have lower head temps, lower turbo temps which leads to lower intake temps. This may be the reason E85 puts out more power than normal gasoline.

From what I've seen on my car, this seems to be true. For example, racing on a 100F day with 91 octane brings my oils temps up to 250-260, where as racing on a 100F day with E85, I normally see oil temps in the 215-225 range. So even with more power, temps are lower.

I'm sure there are other reasons as well, just thought I'd throw this out there.

[AllroadCorbin]

If what I've read is correct, the exhaust gas temp on E85 is several hundred degrees lower than gasoline (1200F vs 1500 IIRC). Due to lower exhaust gas temps, we have lower head temps, lower turbo temps which leads to lower intake temps. This may be the reason E85 puts out more power than normal gasoline.

From what I've seen on my car, this seems to be true. For example, racing on a 100F day with 91 octane brings my oils temps up to 250-260, where as racing on a 100F day with E85, I normally see oil temps in the 215-225 range. So even with more power, temps are lower.

I'm sure there are other reasons as well, just thought I'd throw this out there.

Interesting. But does a cooler burn (temperature alone) actually increase output? It would make sense if it reduced heat soak after multiple runs but create 50+ lb/ft of torque inherently? idk

Arin- get in here haha. bring a calibrator and explain how this shizz works

[adamazing]

PURE Ethanol has an (R+M)/2 of 109. Pure E85 (which has a 15% mixture of gasoline) has an (R+M)/2 of 99. So no matte you and I do, the highest octane rating in our tank using a pure race E85 ordered from Sunoco is 99 (R+M)/2. What I'm wondering is what (R+M)/2 value APR has assumed. Previous research when this corn shit came out claimed it to be well over 110. Some even said 116 which is totally not true. IF that was true, then APRs E85 claimed hp/tq figures would make sense... but given what we now now about the true octane value of E85, it doesn't, and I'm concerned that its over-advanced and can damaged the vehicle over time. Ive logged a lot of big timing retard in the past using E85 and this would explain why. We have an ethanol sensor which changes timing based on a given % of ethanol in the tank, but if the assigned (R+M)/2 variable value in that timing calculation equation in their software is incorrect or too high, then we have a problem....since our cars don't sense "Octane"


Maybe i'm thinking about this all wrong but right now, it doesn't make sense

I still don't agree with your math here. Let's say that pure ethanol has an octane rating of 109 instead like you said - and lets also assume that the fuel manufacturer is using the cheapest possible pump gas to dilute it, 87 octane. There is a 22 point octane difference between them.

Now here is where the blend quality comes into play. My ethanol sensor always reads 69 or 70% That leaves a 30% dilution rate of standard gasoline, not the 50% cut that the equation your using calls for.

30% of the 22 octance point difference is 6.6 points.

So, 109 octane minus 6.6 points is still 102.4 octane.


That's what I meant earlier when I said that the blend of the E85 mixture is more important in order to calculate a more accurate AKI. I;f your sensor is only reading in the 50's and 60's, obviously it's being cut with more regular pump gas to drag that rating down. In which case I would agree with you.

[adamazing]

But I will say this... it's all kinda a moot point anyway. Since no one really has a way to accurately measure octane for ethanol fuel to begin with. The added oxygen, as well as the cooling properties the atomized methanol has in the cylinder add a lot of un-measurable variables that make it a guessing game to begin with.

[AllroadCorbin]

I still don't agree with your math here. Let's say that pure ethanol has an octane rating of 109 instead like you said - and lets also assume that the fuel manufacturer is using the cheapest possible pump gas to dilute it, 87 octane. There is a 22 point octane difference between them.

Now here is where the blend quality comes into play. My ethanol sensor always reads 69 or 70% That leaves a 30% dilution rate of standard gasoline, not the 50% cut that the equation your using calls for.

30% of the 22 octance point difference is 6.6 points.

So, 109 octane minus 6.6 points is still 102.4 octane.


That's what I meant earlier when I said that the blend of the E85 mixture is more important in order to calculate a more accurate AKI. I;f your sensor is only reading in the 50's and 60's, obviously it's being cut with more regular pump gas to drag that rating down. In which case I would agree with you.

I see what you're saying but the Purest form of E85 you can possibly buy is still only 99 Octane. I don't know the math behind it or what the octane of the pure ethanol used in the Sunoco mix is, but the absolute highest octane of E85 you can have in your tank is 99 (R+M)/2. Since it is almost impossible to find E85 that is actually 85% ethanol that means the Octane of pump Ethanol is even lower, which is why Shell and Gulf claim their E85 to be about 94 (R+M)/2. So the absolute best case scenario you'll ever theoretically have is a tank of stuff that's 99 octane.

[b6onboost]

Cooling properties.

Ethanol is still a different chemical which burns much cooler. Lowers block temps, EGTs, IATs, etc. So even if by some math E85 has an octane equivalent to Race Gas, you can still run more timing/boost/etc...with E85.

[AllroadCorbin]

Cooling properties.

Ethanol is still a different chemical which burns much cooler. Lowers block temps, EGTs, IATs, etc. So even if by some math E85 has an octane equivalent to Race Gas, you can still run more timing/boost/etc...with E85.

Ah ok that would make some sense to me But its Octane is significantly lower than some race gas. I guess perhaps that makes a big difference?

[energy_legs]

Ah ok that would make some sense to me But its Octane is significantly lower than some race gas. I guess perhaps that makes a big difference?

The measured octane may be lower, but the adiabatic cooling and latent heat of the fuel mean that the pre-combustion temperatures in the cylinder will be lower meaning you can run more timing. The extra oxygen also helps with HP.

[AllroadCorbin]

The measured octane may be lower, but the adiabatic cooling and latent heat of the fuel mean that the pre-combustion temperatures in the cylinder will be lower meaning you can run more timing. The extra oxygen also helps with HP.

Ah ok that helps explain it a bit


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[Arin@APR]

What the actual octane rating is, doesn't matter. We test, tune, and test again. In the end the sensor reads the content and blends the maps to deliver the correct ignition advance. Ethanol also has properties that are not like other fuels, like cooling and heavy oxygen content, all helping to make it a magical fuel for power (in more quantity.) :)

[hyperunion]

What the actual octane rating is, doesn't matter. We test, tune, and test again. In the end the sensor reads the content and blends the maps to deliver the correct ignition advance. Ethanol also has properties that are not like other fuels, like cooling and heavy oxygen content, all helping to make it a magical fuel for power (in more quantity.) :)

Good deal!... Now we need more e85 pumps available!... Torque is addictive, can't imagine how the k04 guys torque curves are!

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[AllroadCorbin]

What the actual octane rating is, doesn't matter. We test, tune, and test again. In the end the sensor reads the content and blends the maps to deliver the correct ignition advance. Ethanol also has properties that are not like other fuels, like cooling and heavy oxygen content, all helping to make it a magical fuel for power (in more quantity.) :)

Makes sense. I just couldn't wrap my head around how that worked


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[AllroadCorbin]

Good deal!... Now we need more e85 pumps available!... Torque is addictive, can't imagine how the k04 guys torque curves are!

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It doesn't suck


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[Brandon K.]

Was looking at AllroadCorbin's prior post after seeing his Dyno graph. I found his octane discussion interesting.

Something additionally that nobody brought up is (if I remember correctly) alcohol combust more slowly. Therefore the flame front advances more slowly and builds cylinder pressure more slowly allowing for significantly more advanced timing. The knock index is just a fuel's resistance to spontaneous combustion under certain test conditions of temperature and pressure... obviously there's a lot more to a fuel's qualities that.

Nitromethane for example has a piss poor knock index but it's energy and oxygen content (if memory serves) are vastly different from regular fuel. Get everything dialed in correctly and it makes tons of power but get it wrong and it's very likely to blow a motor.


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[AllroadCorbin]

I'm curious what my dyno would look like if I put some GT260+ (104 octane) on my 104 file.


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[Brandon K.]

Only one way to find out. Maybe the dyno shop will give you a discount for another few runs just to see what it does.


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[hyperunion]

I'm curious what my dyno would look like if I put some GT260+ (104 octane) on my 104 file.


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Don't think as much as the e85 blend you used!..

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[johnnySV]

It's hard to find robust answers to the OEM & aftermarket tuning logic, however, my current understanding is that with Gasoline (not e85) a 100 Octane file could be as much as 20 degrees advanced from a 93 Octane file. And it's also my understanding that the ECU, regardless of tune, can only ever retard up to 12 degrees of timing.... which is why people feel the 'risk' of running a 100 octane file when anything below 100 octane is in the combustion chamber.

Can anyone validate this 20 vs. 12 degrees discussion?

Also, any tuner is only tuning a few variables, obviously across a broad high-resolution RPM range. Which variables is APR changing in their e85 file compared to their 100 Octane file?





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[AllroadCorbin]

APR doesn't have an E85 file. They use the ethanol sensor to advance timing


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[johnnySV]

ah, ok, so which APR tune are you running @AllroadCorbin the 93 or 100 Octane?


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[AllroadCorbin]

ah, ok, so which APR tune are you running @AllroadCorbin the 93 or 100 Octane?


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93


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