Ethanol and Octane

[RNorb]

My local gas station (Union 76) carries 90 octane Ethanol free gas. Their premium gas containing 10% ethanol is rated at 92 octane. I'd like to use the ethanol free gas but I'm not sure if I'd be losing power using gas with lower octane rating than what BMW specifies. Any opinions?

[wjbender]

Ethanol will raise octane, but lower fuel mileage, because the energy density of ethanol is less than gasoline. Ethanol is also corrosive and I would avoid it if possible. Consider writing your legislators to eliminate this crony capitalism and unfair tax on us.

[barcelona]

I use Shell (Canada) V power, no ethanol. Law is 5% ethanol average, Shell offers choice: 3 grades are 10, 5 ,0% ( bronze, silver, vpower)


http://pure-gas.org/index.jsp
Not sure about site accuracy as, I cannot determine from whether Esso premium is ethanol free.

[lowlevelhell]

Also, double check what method your station's supplier uses to calculate octane versus what BMW specifies. Usually they're the same, with the number being the (R+M)/2 AKI value but I have occasionally--very rarely--encountered a station whose supplier used RON, or a car whose fuel is recommended in RON vs R+M/2. I have a 35d so I don't know what's written on the der Benziner Motor these days. Anyhow, the two methods produce different numbers.

The other thing to remember is that octane is a bit imprecise to begin with. If the guy before you bought regular, you're putting a hose worth of 87 octane in your tank. It comes out to about a third of a gallon. Not much, but the point is that you're always a bit off on your "recommended" octane. It's an imprecise system at best.

As others have pointed out, ethanol raises AKI value (it doesn't actually increase octane) but yields less energy when burned. So a switch from 92 "octane" gas to ethanol-free 90 will not rob you of any power.

[RNorb]

Thanks for the replies. I definitely prefer the ethanol free gas even though its more expensive. I think I'll alternate fill-ups between premium and ethanol free, should make for a good compromise.

[42pilot]

If you could get E85, I would do that. Ethanol is much more predictable in its burn properties than gas and really plays well in turbo motors. Granted it takes more ethanol than gas for a given output, but you will not grenade your engine due to detonation. The last turbo Porsche engine I built and tuned is set up to take E85 because of the power ethanol can safely produce - this motor should be over 850 hp on E85 (below is a magazine spread on the car from this month - note the alternative fuel auto tag). And ethanol has been around for so long, most every part it comes in contact with on newer engines will not hurt it.

The primary problem with ethanol is that it is hygroscopic - it absorbs water big time. It even absorbs water from ambient air and that is the real problem with our fuel pumps, fuel injectors and poor performance. Water will f-up these parts very quickly because it does not have lubricating properties of fuel. I think the gas fuel pressure in these motors is somewhere between 45 - 60 psi, so those in-line pumps spin fast. Get water in there, let it sit overnight, and you've got rust. The direct fuel injectors used in our gas motors wouldn't last long either (I'm talking declining efficiency first, then failure).

So, what fuel would I chose? The highest quality, highest volume (in terms of sales) brand station convenient for you. Your car is engineered to take a pretty wide range of fuel quality. Choosing a fuel for max power is chasing a horse you won't catch - unless its oxygenated like the older ELF racing fuel. Otherwise, octane will not add power you will feel, however you might feel it run smoother since the fuel is burning in the combustion chamber rather than exploding.

Now, if you run cheaper, lower octane fuel in your turbo car, you will notice a loss in power, but this is because the tuning strategy in the ECU is detecting detonation (or rougher running engine) and retarding the timing and lowering boost to keep you from toasting the motor. But between 90 and 93 octane, you won't notice a thing. Buy from a quality source and go have fun.

[lowlevelhell]

Originally Posted by 42pilot

If you could get E85, I would do that. Ethanol is much more predictable in its burn properties than gas and really plays well in turbo motors. Granted it takes more ethanol than gas for a given output, but you will not grenade your engine due to detonation. The last turbo Porsche engine I built and tuned is set up to take E85 because of the power ethanol can safely produce - this motor should be over 850 hp on E85 (below is a magazine spread on the car from this month - note the alternative fuel auto tag). And ethanol has been around for so long, most every part it comes in contact with on newer engines will not hurt it.

The primary problem with ethanol is that it is hygroscopic - it absorbs water big time. It even absorbs water from ambient air and that is the real problem with our fuel pumps, fuel injectors and poor performance. Water will f-up these parts very quickly because it does not have lubricating properties of fuel. I think the gas fuel pressure in these motors is somewhere between 45 - 60 psi, so those in-line pumps spin fast. Get water in there, let it sit overnight, and you've got rust. The direct fuel injectors used in our gas motors wouldn't last long either (I'm talking declining efficiency first, then failure).

So, what fuel would I chose? The highest quality, highest volume (in terms of sales) brand station convenient for you. Your car is engineered to take a pretty wide range of fuel quality. Choosing a fuel for max power is chasing a horse you won't catch - unless its oxygenated like the older ELF racing fuel. Otherwise, octane will not add power you will feel, however you might feel it run smoother since the fuel is burning in the combustion chamber rather than exploding.

Now, if you run cheaper, lower octane fuel in your turbo car, you will notice a loss in power, but this is because the tuning strategy in the ECU is detecting detonation (or rougher running engine) and retarding the timing and lowering boost to keep you from toasting the motor. But between 90 and 93 octane, you won't notice a thing. Buy from a quality source and go have fun.

I doff my cap to you for an excellent post.

Not that it matters to most folks here probably, but ethanol fuel additives can wreak havoc on an old engine. Ethanol fuel ate right through the diaphragms on my ZS CD-175 carbs (go ahead and have a nice chuckle at ZS carbs anyway). Turns out the supplier didn't think to make their rebuild kit ethanol safe. WOMP WOMP :roll eyes:

[cit1991]

You can run either 90 octane E0 (non ethanol) or 92 octane E10 (with 10% v/v ethanol) safely. The F15 is not rated for E85 (which BTW is not 85% ethanol).

Ethanol raises octane rating, but when blending ethanol, they start with a lower octane base fuel, so the blend is 92 octane (or whatever it's advertised to be). That basestock is called RBOB (reformulated blendstock for oxygenate blending) and there are other differences between RBOB and E0 finished gasoline.

Ethanol has 2/3 of the energy content per gallon of E0 gasoline. So a 10% blend has about 3.3% less energy per gallon. If you run 90 octane E0, the engine will pull a little boost and/or timing at full throttle so it'll cost you power. But at part throttle (where you burn most gas) it probably won't have to pull anything.

So, the 90 E0 might cost you some power (when you're pushing it), but will probably give you a little more mileage.

[42pilot]

Originally Posted by cit1991

You can run either 90 octane E0 (non ethanol) or 92 octane E10 (with 10% v/v ethanol) safely. The F15 is not rated for E85 (which BTW is not 85% ethanol).

Ethanol raises octane rating, but when blending ethanol, they start with a lower octane base fuel, so the blend is 92 octane (or whatever it's advertised to be). That basestock is called RBOB (reformulated blendstock for oxygenate blending) and there are other differences between RBOB and E0 finished gasoline.

Ethanol has 2/3 of the energy content per gallon of E0 gasoline. So a 10% blend has about 3.3% less energy per gallon. If you run 90 octane E0, the engine will pull a little boost and/or timing at full throttle so it'll cost you power. But at part throttle (where you burn most gas) it probably won't have to pull anything.

So, the 90 E0 might cost you some power (when you're pushing it), but will probably give you a little more mileage.

According to government regulations, E85 can be between 51% and 83% ethanol, and it has to be ethanol (see Dept of Energy website for more info). The reason for the delta is geography and environment (temps - for cold start, proper vaporization, etc). As for the base stock, this doesn't surprise me. The E85 we have at our fave station, is >80% ethanol. This pump is used mostly by the ultra-high HP guys putting out 1200 hp on twin turbo American muscle cars.

Anyway, to give you an idea of the difference in equipment needed to run E85, the fuel injectors on the car I mentioned in my post are nearly twice as large than for 100% petrol (100lb injectors for E85 vs 60lb for gas). At WOT (wide open throttle) on pump gas, the duty cycle on the flex fuel injectors are just over 25%!

I think it's possible the ECU will pull timing out on 90 octane E0, but because of the difference in quality fuels in the US, they've probably already pulled all the timing out (this is what "tuners" are adding back in ECU tunes for my SL550 - adding a couple of degrees timing). Besides, timing is not horsepower - it's torque. Above 5000-ish RPM, on a forced induction motor, timing can be near 15 degrees or less. My personal turbo Porsche, at WOT and 5000 rpm, producing 525 hp and 500 lb ft torque had total timing of 12 degrees. This is much different that the 39 degrees at 3500 rpm. Anyway, none of us are going to feel a couple of degrees taken out for 90 vs 93 octane.

I didn't know these cars can't take flex fuels - odd. I have a 35d, so my bad.

Sorry to the OP for hijacking the thread.

[wjbender]

Originally Posted by 42pilot

According to government regulations, E85 can be between 51% and 83% ethanol, and it has to be ethanol (see Dept of Energy website for more info). The reason for the delta is geography and environment (temps - for cold start, proper vaporization, etc). As for the base stock, this doesn't surprise me. The E85 we have at our fave station, is >80% ethanol. This pump is used mostly by the ultra-high HP guys putting out 1200 hp on twin turbo American muscle cars.

Anyway, to give you an idea of the difference in equipment needed to run E85, the fuel injectors on the car I mentioned in my post are nearly twice as large than for 100% petrol (100lb injectors for E85 vs 60lb for gas). At WOT (wide open throttle) on pump gas, the duty cycle on the flex fuel injectors are just over 25%!

I think it's possible the ECU will pull timing out on 90 octane E0, but because of the difference in quality fuels in the US, they've probably already pulled all the timing out (this is what "tuners" are adding back in ECU tunes for my SL550 - adding a couple of degrees timing). Besides, timing is not horsepower - it's torque. Above 5000-ish RPM, on a forced induction motor, timing can be near 15 degrees or less. My personal turbo Porsche, at WOT and 5000 rpm, producing 525 hp and 500 lb ft torque had total timing of 12 degrees. This is much different that the 39 degrees at 3500 rpm. Anyway, none of us are going to feel a couple of degrees taken out for 90 vs 93 octane.

I didn't know these cars can't take flex fuels - odd. I have a 35d, so my bad.

Sorry to the OP for hijacking the thread.

We should all be writing our elected officials to put an end to the ethanol mandate as it is well past being useful. It was originally conceived as a way to reduce dependence on imported oil. with at emergence of fracking there is plentiful domestic supply of gasoline. Now ethanol it is nothing but crony capitalism. Straight petrol would cost less.