[TOWMA8R]

Octane-rating (AKI, not "octane") mixes linearly same as the equations I posted earlier.

Lets assume E10 and E85 really are 10% and 85%. Correct the numbers based on your test results.

I don't see AKI listed on E85 pumps around here but most references say 104 AKI if it really is 85%. It might be 100 AKI for lesser proof.

To mix E10 and E85 for E30:

0.9 gasoline + 0.1 ethanol + X * ( 0.15 gasoline + 0.85 ethanol ) = ( 1 + X ) * (0.70 gasoline + 0.30 ethanol)

After much fun math: add 0.364 gallons of E85 to 1.0 gallons of E10 to make E30.

A = 0.90 for 90% gasoline in E10
B = 0.15 for 15% gasoline in E85
C = 0.70 for 70% gasoline in E30

( A - C ) / ( C - B ) = ( 0.90 - 0.70 ) / ( 0.70 - 0.15 ) = 0.363636363636364

1.0 gallons of 87 AKI plus 0.364 gallons of 104 AKI E85:
(1.0 * 87 + 0.364 * 104) / ( 1.0 + 0.364 ) = 91.5 AKI

Some say E100 is 107 AKI and 85 AKI is the base gasoline used. That produces 87.2 AKI for E10, 103.7 AKI for E85, 91.6 AKI for E30.

87 AKI E10 needs 84.7 AKI E0
89 AKI E10 needs 87.0 AKI E0
91 AKI E10 needs 89.2 AKI E0
93 AKI E10 needs 91.4 AKI E0

Not all E85 is actually 85. My station varied between E76 and E80...... I have seen it as low as E68 So your calculation would be off....... you need to text to content of the fuel every month, minimum.... plenty of apps avail that make this a pretty user friendly process.

 

[TOWMA8R]

Oh…I did not even notice that till now, hahah.

OAR is your Octane Adjust Ratio. To put it in simple terms, it provides you a good idea on if your fuel is adequate. It will always be specific to who wrote the tune, and/or how the tune was designed. No two trucks will be the same.

This ratio allows the calibration to use a multiplier which either advances/retards on-top of the base timing tables. Hence the performance difference when running 87 to 91. Overall it uses KR feedback to determine fuel quality for the calibration.

SCT
Negative OAR - Good.
Positive OAR - Bad/Ok.

There are others who can explain it far better than me.

I know positive OAR is bad, stock tunes can have it.... how much positive is acceptable and where do you start to worry?

 

[mass-hole]

I know positive OAR is bad, stock tunes can have it.... how much positive is acceptable and where do you start to worry?

87 octane should be an oar of 0 best i can tell. Maybe even slightly negative. At least on a tune using the stock timing tables.

If you +1 you are in rough shape.

I think these trucks could run 85 if you wanted to but it would suck.

 

[Rhydon]

E30-40 Commute daily. 20k miles and counting

This is encouraging.

 

[FanaticalKilla]

Is it this simple? Just asking because I honestly do not know the answer.

Hp for hp to do the same job or same output. My math was a little skewed that someone already put out.

 

[TOWMA8R]

87 octane should be an oar of 0 best i can tell. Maybe even slightly negative. At least on a tune using the stock timing tables.

If you +1 you are in rough shape.

I think these trucks could run 85 if you wanted to but it would suck.

This is where the knock thing gets confusing. I have seen stock trucks and mustangs with crazy knock but the timing being pulled away is the safe guard right? And some say slight positive is ok in most cases..... Not sure why I am not understanding this better.....

 

[SrpRacing]

KR is not actual knock. It’s the amount of timing the truck pulls( retards ) to prevent knock/detonation. The sensor itself picks up frequencies in which it references a table. Ford spent thousands of hours dialing in knock sensor feedback.

Some positive KR is not an issue at all. The calibration is just fine tuning the amount of timing it can add based on the fuel. It’s all about efficiency. That’s why you will always have more KR under light load. The calibration runs as much timing as the table will allow for emissions and fuel efficiency.

OAR will do it’s job and adjust the timing tables if the KR is excessive. If your OAR were maxed out positive(crappy fuel), then I would start to worry. But the truck would throw itself into a Knock Performance Limp mode.

 

[N4HHE]

I know positive OAR is bad, stock tunes can have it.... how much positive is acceptable and where do you start to worry?

If it is not running bad and MPG reasonable don’t worry about it. However one should note the source and consider others if one can get lower and negative numbers for same price. I’m getting 22 MPG around town on +0.25 OAR. Have a 130 mile day coming up. Not going to pass judgement until the engine has an honest chance to calibrate this fuel.

 

[SrpRacing]

OAR can be very different between tunes. The stock tune is very conservative.

 

[Rhydon]

OAR can be very different between tunes. The stock tune is very conservative.

What would you say is the best overall way to track your OAR and KR in real time?

 

[snakebitten]

With an ODB driven device.
These are no longer available, but I use an Ngauge. Can display 6 Pids of your choice. (from better than 100)

You can also do the same with a smartphone or tablet.

 

[tvsjr]

If it is not running bad and MPG reasonable don’t worry about it. However one should note the source and consider others if one can get lower and negative numbers for same price. I’m getting 22 MPG around town on +0.25 OAR. Have a 130 mile day coming up. Not going to pass judgement until the engine has an honest chance to calibrate this fuel.

You're running stock tune and seeing positive OAR? I'd be looking for a better fuel source... sounds like absolutely garbage gas.

 

[Roushracing1]

Octane-rating (AKI, not "octane") mixes linearly same as the equations I posted earlier.

Lets assume E10 and E85 really are 10% and 85%. Correct the numbers based on your test results.

I don't see AKI listed on E85 pumps around here but most references say 104 AKI if it really is 85%. It might be 100 AKI for lesser proof.

To mix E10 and E85 for E30:

0.9 gasoline + 0.1 ethanol + X * ( 0.15 gasoline + 0.85 ethanol ) = ( 1 + X ) * (0.70 gasoline + 0.30 ethanol)

After much fun math: add 0.364 gallons of E85 to 1.0 gallons of E10 to make E30.

A = 0.90 for 90% gasoline in E10
B = 0.15 for 15% gasoline in E85
C = 0.70 for 70% gasoline in E30

( A - C ) / ( C - B ) = ( 0.90 - 0.70 ) / ( 0.70 - 0.15 ) = 0.363636363636364

1.0 gallons of 87 AKI plus 0.364 gallons of 104 AKI E85:
(1.0 * 87 + 0.364 * 104) / ( 1.0 + 0.364 ) = 91.5 AKI

Some say E100 is 107 AKI and 85 AKI is the base gasoline used. That produces 87.2 AKI for E10, 103.7 AKI for E85, 91.6 AKI for E30.

87 AKI E10 needs 84.7 AKI E0
89 AKI E10 needs 87.0 AKI E0
91 AKI E10 needs 89.2 AKI E0
93 AKI E10 needs 91.4 AKI E0

Wow, what an explanation. I think I gained 10 IQ points just reading this!

 

[Rhydon]

With an ODB driven device.
These are no longer available, but I use an Ngauge. Can display 6 Pids of your choice. (from better than 100)

You can also do the same with a smartphone or tablet.

Fair enough, I use a BDX. I couldn't find any KR or OAR pid's. Might have to import those later if they aren't already there. Purchasing a couple tunes tonight. I'm diving in.

Edit: BTW thank you for that picture that was actually incredibly helpful to me.

 

[TOWMA8R]

KR is not actual knock. It’s the amount of timing the truck pulls( retards ) to prevent knock/detonation. The sensor itself picks up frequencies in which it references a table. Ford spent thousands of hours dialing in knock sensor feedback.

Some positive KR is not an issue at all. The calibration is just fine tuning the amount of timing it can add based on the fuel. It’s all about efficiency. That’s why you will always have more KR under light load. The calibration runs as much timing as the table will allow for emissions and fuel efficiency.

OAR will do it’s job and adjust the timing tables if the KR is excessive. If your OAR were maxed out positive(crappy fuel), then I would start to worry. But the truck would throw itself into a Knock Performance Limp mode.

Sir, thank you for the feedback, I somewhat get it now!

 

[mass-hole]

Fair enough, I use a BDX. I couldn't find any KR or OAR pid's. Might have to import those later if they aren't already there. Purchasing a couple tunes tonight. I'm diving in.

Edit: BTW thank you for that picture that was actually incredibly helpful to me.

They might be called knock retard and octane adjust ratio/learned octane ratio.

 

[N4HHE]

In the OBDLink app I had to manually add the PID for OAR. Don't remember what I did other than enter the numbers then select a "gauge" to display the value. Set the display range to -1 to +1 as it defaulted to -1000 +1000.

I the math post above, late at night, the main equation is correct but needlessly complicated by including both gasoline and ethanol in one. Easier to solve for mixing 90% gasoline with 15% gasoline to get a 70% mixture. Or you will get the same answer mixing 10% ethanol with 85% ethanol to get a 30% ethanol mixture. The gasoline one is the A, B, C, equation.

 

[mass-hole]

In the OBDLink app I had to manually add the PID for OAR. Don't remember what I did other than enter the numbers then select a "gauge" to display the value. Set the display range to -1 to +1 as it defaulted to -1000 +1000.

I the math post above, late at night, the main equation is correct but needlessly complicated by including both gasoline and ethanol in one. Easier to solve for mixing 90% gasoline with 15% gasoline to get a 70% mixture. Or you will get the same answer mixing 10% ethanol with 85% ethanol to get a 30% ethanol mixture. The gasoline one is the A, B, C, equation.

In my OBDLink app its in the Ford Enhanced Diagnostics addon as Learned Relative Octane Adjustment and its -100% to +100% and the values are inverted. So +100% is a -1

 

[Rhydon]

Just want to give a shout-out to everyone who did/is participating in this thread and to Torrie. I'm finally diving into an e30 and e50 tune And learning a ton about my truck along the way. That's what it's all about right? And beating all the mustangs 😆

 

[Scott91370]

Is it this simple? Just asking because I honestly do not know the answer.

From my dealings with ethanol I have found that e10 (regular pump gas) will get you XX mpg and e85 will get you approximately 25% less. So if you're getting 10mpg you can expect right around 7.5. Since you're going to e30 it won't be quite that drastic - maybe a loss of 5-10% from what you're currently getting. More or less in winter.