High gas prices..how about regular?

[JCL]

Originally Posted by LudjakR1

I still think that best is 92 93, from the old saying "you are what you eat",

Actually, the best for the engine is the lowest AKI that doesn't cause the timing to be retarded due to knocking. 92 is the safest, not the best.

Originally Posted by HPIA4v2

Isn't our rule of thumbs always when in doubt read the user manual (or in this case gas filler door?) And what does it say in there?

That label, written by BMW lawyers, says to use 91 (on the basis that even if you get a crap tank of 91, it will probably be good enough for what the engine was designed for) Classic CYA. And yes, I agree, if one is in doubt, it is the easiest thing to do. Similarly, one should make sure to also follow the manual's instructions to only use BMW OE parts and BMW dealer service facilities, and not to install any aftermarket accessories.

[LudjakR1]

[QUOTE=JCL;813836]Actually, the best for the engine is the lowest AKI that doesn't cause the timing to be retarded due to knocking. 92 is the safest, not the best.

did not know that, thank you sir for that post

[JCL]

Originally Posted by Buzzcut

We shall see what the consequences are. I will be sure to let everyone know. I'm thinking of starting another blog about the experience. The only problem is that, with 96k miles, it wouldn't be unusual to have to replace an injector or a fuel pump, so it is going to be more difficult to say what caused the failure than it would be on a new car, as the Saab was.

It will be interesting to hear.

I am just wondering what the upside is. Is your experiment to help reduce greenhouse gases?

From a cost standpoint, going from $3.70 a gallon (premium) to $3.00 a gallon (E85) is a 19% savings. But from an energy standpoint, ethanol has 26% less energy (volumetric), so E85 has 22% less energy, and if you are only saving 19% you are taking a 3% hit in the pocketbook. That hit will be reduced as you are blending gasoline and E85, but it is still a negative. Add in the risk of component damage, and it sounds like a no-win.

If you modify the engine to take advantage of the cooling effect of ethanol, I can see getting some of those losses back.

You mentioned 105 AKI for ethanol, and that sounded high, so I checked it online. I found references of 94-96 AKI, and a description of why 105 doesn't represent the real AKI, having to do with the test procedure. One source here:

Renewable Fuels Foundation Guide to Spark Ignited Engine Fuel Quality

[Buzzcut]

You should read my blog.

E85 is 105 octane. The Drunken Swede: Search results for 105

It says so on the pump.

What's the point of mixing? It's science. No seriously, I just like debunking all the BS about ethanol that's on the internet.

[bigwave2255]

i only use high octane in my jeep cherokee, it pings its head off on standard, i did the numbers on my previous cars, mazda 6 and honda accord and both got better miles per dollar on high octane, i also run it in my boat (twin 4.3 efi,s) cant hear them if they were pinging and the added cost is cheap insurance in my view.

also i tend to find they run smoother and idle sweeter than on low octane fuels, wont use ethanol under any circumstances, especially in a boat

oh and i use high octane diesel in my X

[JCL]

Originally Posted by Buzzcut

You should read my blog.

E85 is 105 octane. The Drunken Swede: Search results for 105

It says so on the pump.

What's the point of mixing? It's science. No seriously, I just like debunking all the BS about ethanol that's on the internet.

You should read my link

Need to be careful of labels on pumps. 105 is the blending octane, ie a fictional number that is used to simulate the effect of blending small amounts of ethanol into gasoline. It is used only because the properties do not blend linearly.

The actual octane (AKI) of E85 can better be determined by testing using both the Motor and Research methods, in actual test engines. That process found that E85 has an AKI around 94-96 as a true octane rating.

The clip below is from the link I provided above.

But since you are mixing E85 and gasoline, and the results are not linear, it is perhaps a moot point.

So, if you are using around 40% E85 (when it is 85, not when it is 70) then you should see a fuel consumption penalty of 22% * 0.4 = 9%. That seems pretty close to your real world results on the SAAB from a quick scan. If so, no financial benefit at current price advantage (except for the farmers).

I like science too

[Fraser]

Originally Posted by Buzzcut

I started mixing E85 into my gas.

Good luck.

Regardless of the cost benefit, if there is one, and how your X will run in the short-term, you risk degradation of your fuel-system components in the long run by running the percentages of ethanol you are talking about.

[1stE53]

Originally Posted by 4MoJoe

I switched 4 tanks ago to regular. I actually am getting better mileage. And I can't explain it. We went on a 600 mile round trip drive this last weekend, I computed my mileage and it was 26mpg for freeway. I was kind of blown away. I asked at the station I go to and they use 10% ethanol in the Premium but not in the Regular...

that is ass backwards. There is your answer, ethanol takes 24% more fuel to go the same distance, so 10% would answer why you are getting better mileage with regular NON ethanol. In MO it is the other way around. Reg gas has Ethanol (not advertised) and Prem is real gas!!!!

[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.