High gas prices..how about regular?

[JCL]

Running 87 AKI doesn't do any damage. Neither does running 89 AKI.

You MAY lose power and mileage. You may not. It depends entirely on your local fuel. Fuel varies so much across North America in terms of quality that it is impossible to take another reference for your local conditions, unless that driver is using the same pumps you are.

My best mileage ever on my X5 was with 89. No loss of power.

Only way to know if the timing is being retarded is to try a full tank or two, and measure your mileage carefully. If it doesn't lose any mileage, go ahead and keep using it. If you notice a difference, decide if the penalty is worth it.

[o. l. t.]

Japanese cars run like crap on 87 (high compression VVTI engines), but the German cars seem to not skip a beat. All my Germans have ran like a top on 87.

[1stE53]

Originally Posted by JCL

Running 87 AKI doesn't do any damage. Neither does running 89 AKI.

You MAY lose power and mileage. You may not. It depends entirely on your local fuel. Fuel varies so much across North America in terms of quality that it is impossible to take another reference for your local conditions, unless that driver is using the same pumps you are.

My best mileage ever on my X5 was with 89. No loss of power.

Only way to know if the timing is being retarded is to try a full tank or two, and measure your mileage carefully. If it doesn't lose any mileage, go ahead and keep using it. If you notice a difference, decide if the penalty is worth it.

Is your engine louder using lower than 91? Anti Knocking Index

[Buzzcut]

For some reason I couldn't open that pdf. I would like to take a look at it.

That's the first document I've ever heard of suggesting that E85 has octane as low as 94 or 96. During my initial research, I found a lot of references that had pure ethanol at 113 octane.

The non-linearity of blending is a big problem for me. I've got a spreadsheet that I use to figure out the blend, and it is a straight line linear calculation, so I could be off.

Another big problem is the variability of E85 itself. It's really E70 right now. Come April, it will briefly be E79, and then it will be E83 through the summer. It is never really E85. My spreadsheet takes this into account, but I can never really know exactly what is in the tank. I just assume that E85 is 100 octane, regardless of the actual ethanol content. I should probably make an effort to adjust that a bit based on real ethanol content.

I do have the ability on the Scangauge to see timing, so perhaps I can use that to get some idea of if the timing is being retarded or not, which would give some indication of the true octane.

[JCL]

Originally Posted by Buzzcut

For some reason I couldn't open that pdf. I would like to take a look at it.

That's the first document I've ever heard of suggesting that E85 has octane as low as 94 or 96. During my initial research, I found a lot of references that had pure ethanol at 113 octane.

The non-linearity of blending is a big problem for me. I've got a spreadsheet that I use to figure out the blend, and it is a straight line linear calculation, so I could be off.

Another big problem is the variability of E85 itself. It's really E70 right now. Come April, it will briefly be E79, and then it will be E83 through the summer. It is never really E85. My spreadsheet takes this into account, but I can never really know exactly what is in the tank. I just assume that E85 is 100 octane, regardless of the actual ethanol content. I should probably make an effort to adjust that a bit based on real ethanol content.

I do have the ability on the Scangauge to see timing, so perhaps I can use that to get some idea of if the timing is being retarded or not, which would give some indication of the true octane.

Sorry, the pdf opens fine for me. I have attached the link the the Renewable Fuels Foundation website, below; perhaps that will help. RFF is in the business of promoting renewable fuels, so they are not against ethanol. They publish documents for auto technicians, that is what this file is. I like that they seem to have less hype, and more facts, compared to some of the stuff out there.

Auto Technicians | Renewable Fuels Foundation

There are a lot of different numbers published for both MON and RON for ethanol, up to the 120 range. The problem is that they are theoretical, not practical. Octane numbers are not a physical property (since gasoline doesn't necessarily have any actual octane in it) but rather a test result of how an engine performs with a sample fuel. Ethanol has much larger differences between MON and RON than gasoline, so it just isn't predictable using gasoline formulas.

Agree that the variability of E85 makes it tough. As the song says, "it isn't always what it says on the tin." Also, since there are no regulations covering AKI labelling for E85, they can put whatever they like on the pump.

I wouldn't expect that you will see the timing retarded at all, since any of the likely AKI numbers are better than premium, and so you will have some boost above the 87 you are using as a base stock.

[JCL]

Originally Posted by 1stE53

Is your engine louder using lower than 91? Anti Knocking Index

No, the engine is not louder. There is no physical knocking. If the fuel was not of sufficient AKI to prevent knocking, the DME would retard the timing. In both cases you would not hear anything. If the timing is retarded, though, you could see less power for a small fraction of the time (timing won't be retarded continuously, just when knocking could occur)