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'79 911SC Targa
 
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Question Ethanol verse Octane

The question is, if you were given an ethanol free option (for your non-daily driver) at 90 octane, OR a 93 octane fuel with 10% ethanol, which would you choose?
This is more of an opinion question, but any and all facts on the topic are always welcome.

I know the effects that ethanol fuel can have on a car’s fuel system when it is not a daily driver, which mine is not. I try to give it a good run once or twice a month, but that gets more difficult in the summer with the rain and heat here in Florida. A full tank of gas will last me about 3 months.
I also understand the need for higher octane fuel to get a good burn, prevent detonation and get a more even burn across the cylinder head.
Recently, a local station started selling ethanol free fuel. It comes at a premium price, but it is worth the benefits. However, the fuel is rated at only 90 octane.

I know that the octane value is a product of two values, but these are not given at the pump so I don’t know what they are. I also know that because if this rating, it is possible that not all 90 octane fuel is created equal. (This is in the same way as your 100 watt head unit amp can (will) be out performed by a 50 watt high current amp.)

Anyway… which would you put in your car?

Mine is a ’79 911SC with the stock 3.0L and stock CSI.

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Old 06-09-2015, 07:25 AM
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Good question, I've also been wondering about that, 90 vs 93 with Et for my collection of old cars.
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Old 06-09-2015, 07:46 AM
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The owner's manual recommends running ethanol-free fuel if possible, so that's good enough for me. Running stock or even slightly advanced timing, 90 octane should be fine.
Old 06-09-2015, 08:14 AM
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EPA says 10% ethanol fuel will give a 3% reduction in gas milege, due to ethanol containing 2/3 the energy contained in an equal amout of gasoline. Also the damn ethanol absorbs water, not good in a car that is a garage queen! Your SC is built to run fine on 87 octane reg gas, so 90 octane non ethanol is a great choice. Don't think the gas milege difference will make up for the price diffential for the ethanol free stuff, but what the hell, you're driving a Porsche!
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Old 06-09-2015, 08:35 AM
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Be careful not to confuse the energy potential of the fuel with its octane rating. Octane measures the compressibility of the fuel before it detonates; the higher the number, the higher the compression ratio possible before knocking. Energy potential is measured using HHV or LHV (higher heating value/lower heating value). Ethanol makes higher octane (low compressibility), but also has lower energy potential (by 25-30%). It also is more hydroscopic, so there is the potential for corrosion in older engines. Therefore, you could go for ethanol free, unless you have a higher compression engine that really needs the octanes (Euro spec).
Old 06-09-2015, 08:58 AM
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The feedback is great and appreciated.
What I find just as interesting, in a good way, is that the feedback is unanimous. Not to often you can get a bunch of cars guys to agree on something. )

Ethanol free at 90 octane it is!
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Old 06-10-2015, 03:25 AM
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I'm not in that camp. I'll take 93 E10, but I'm boosted and EFI.

But what I really want is E85, since it's cheap racing fuel.
Old 06-10-2015, 03:45 AM
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I've long thought about the same question. If you drive a car daily and keep burning up the fuel, the ethanol is probably not harmful and does give an octane boost. However, if it sits for long, bad things happen to carborators. I wonder what folks like Jay Leno or Jerry Seinfeld do to avoid issues in their collections? I think that keeping tanks fairly empty and using some additives like the new Stabil 360 May be the way to go.
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Old 06-10-2015, 04:40 AM
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I've been adding this stuff to my car with NO ethanol 91 octane...'bout 1/2 can per tank.My car LOVES it, never ran better !!
Old 06-10-2015, 04:55 AM
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One point on ethanol or any alcohol based fuel: these fuels have O2 molecule(s) bound to the fuel. This is why hi-perf motors run on pure alcohol based fuels. This means that O2 enters into the mixture from within the fuel itself, so you get 21% O2 from the intake air then you have extra O2 in the fuel and this allows for more torque development without forced induction.

Often folks think that you run very rich with ethanol (7.0-9.0 AFR) but the truth is this is because some of the O2 is baked into the fuel.

In summary: a given motor running on E85 vs standard Gasoline will generally develop more torque and HP on E85 the gains can be substantial, from 10-20% HP gains! You will not get great MPG but you certainly will get more power. And you will also need to flow about 20% more fuel at any given engine condition.

If you wish to really understand these principles I recommend reading the 2 books published by Greg Banish, search him on Amazon. These 2 books are the best written books I've seen on tuning principles and covers fuel sources in detail.
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Old 06-10-2015, 05:07 AM
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Quote:
Originally Posted by Jack Stands View Post
I've long thought about the same question. If you drive a car daily and keep burning up the fuel, the ethanol is probably not harmful and does give an octane boost. However, if it sits for long, bad things happen to carborators. I wonder what folks like Jay Leno or Jerry Seinfeld do to avoid issues in their collections? I think that keeping tanks fairly empty and using some additives like the new Stabil 360 May be the way to go.
I think leaving tanks full with E10 is best because when full you have far less air in the tank and air has moisture that binds to the ethanol. The binding of the water to the ethanol is the bigger problem, if the ethanol separates from the fuel that's not desirable but if it separates and then binds with water that's the bigger issue.

I vote for leaving tanks full during storage of 2 weeks or more. Plus a tank full of liquid fuel will not corrode below the fuel line.
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Old 06-10-2015, 05:12 AM
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In a car like the SC, I'd probably go with the lower octane, but ethanol free type. If it was in a higher state of tune, the choice would be more difficult. I am lucky enough to have ethanol free 94 available in my area which I use in my 85 and 96. A full tank will have less fuel surface area in contact with the air and therefore will likely absorb less water but even if you maintain a full tank when not in use, you have ethanol all through your fuel system breaking down seals and lines. When travelling outside my area I must use ethanol but I always make sure to be mostly empty when arriving back so I can fill with the good stuff upon arrival. Cheers
Old 06-10-2015, 05:43 AM
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My friend that travels the world for the Gates Corporation (fuel line, radiator hoses, belts etc.) performing technical training seminars claims that the ethanol blended fuels go into "phase separation" after 16 days. Given that, and the fact that my SC won't make it through the dip and incline from the street to my driveway with more than a half tank of fuel I tend to try and keep a fresh half tank of fuel in the car every two weeks.

Also, a year or so ago I had a conversation with a fuel tanker driver at a Valero station as I wanted to get his thoughts on the ethanol blended fuels vs. the non ethanol stuff. His take was all the non ethanol fuel was 90 octane, when they blend the ethanol it raises it to 93 octane. I then asked him where they delivered the most fuel and as I suspected it was the grocery store chain in the more "wealthy" neighborhood across town where the Doctors and Lawyers and such drive BMW's, Lexi, etc. so that confirmed my insight on where to find the "fresh" stuff.

Last edited by SCadaddle; 06-10-2015 at 08:38 AM..
Old 06-10-2015, 08:28 AM
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You will always get moisture in the fuel system if you subject the car to changing temperatures.
The ethanol will mix with that and allow the moisture to be combusted, instead of the water being left at the bottom of the tank rusting....
In cold climates you used to add ethanol in the winter so fuel lines wouldn't freeze and plug up. Now you don't need to because there is always 5% ethanol in the gas.

I think ethanol can be a good fuel for our cars, if we adapt them. It has the potential for more power for two reasons:
1. Higher octane, you can use more aggressive ignition.
2. Burns cooler, that can't be bad in our cars.

In a watercooled engine you can usually extract 3-4% more power with E85 after a remap, according to my dyno guy.
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Old 06-10-2015, 09:32 AM
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Here's ethanol molecule structure:
http://i.imgur.com/cxEuy6L.gif

Notice 6 hydrogen parts to 1 O2 part

Here's basic Gasoline:
http://upload.wikimedia.org/wikipedia/commons/1/16/Chemical_Principles,_Molecules_4.png

Notice 18 parts of hydrogen but no O2.

You need to pair up the Hydrogen with O2 to burn it. This means that with Gasoline you only get the O2 from the intake air. So no matter how much energy the gasoline has you can't put more into the motor than the O2 the motor can ingest. You need to really think about this for a bit so it sinks in.

No matter how much energy potential the Gasoline has you are choked off by the amount of O2 the motor can get into it.

Now let's contrast this with Alcohol or Ethanol: even though ethanol has less energy potential per gram than gasoline it has a huge advantage since for every 6 'H' particles it has one built in O2 particle, this means we have a free bonus energy potential since 1 of the 6 H particles is already paired up with a free O2 built into the fuel. This means we only need 5 more O2s for the other 5 Hs. Sure we need to flow a lot more ethanol in grams than we'd need if using gasoline but that's not the point. The point is that the ethanol has about 20% of the needed O2 baked into the fuel (1 out of 6 Hs has the O2 paired up) 6/5=1.2 or 20%

So it's true that ethanol MPG is not so great but that's because you're paying for the O2 in the fuel as well. With Gasoline you are only paying for the Hs and the O2 comes from the ambient air.

That's my best attempt to explain Ethanol vs Gasoline
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Last edited by scarceller; 06-10-2015 at 10:17 AM..
Old 06-10-2015, 09:57 AM
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Quote:
Originally Posted by scarceller View Post
... The binding of the water to the ethanol is the bigger problem, ...
This.

My SC gets much better mileage out of non-ethanol fuels.
Much better than the supposed 3% calculation.
I suspect that the ethanol fuels often come out of the pump pre-hydrated.

BTW, 10% ethanol fuels can support about 10% water. :-/
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Old 06-10-2015, 10:23 AM
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Oh, and while that water will help quell detonation (essentially giving high octane rating) it is cooling the burn, slowing the burn. That is likely a sub-optimal situation for most conditions.
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Old 06-10-2015, 10:27 AM
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som facts & rumors on ethanol for you

The fact that you might not get more power filling up with E10 compared to regular fuel is because your engine is not tuned to run om E10.
On an early car you do not have an ECU regulating ignition. The benefits on power gain is obtained by more aggressive ignition. A custom chis or remap will make it worth running on E10 for all you power addicts

Having mostly been using ethanol on boosted cars i can give you an example. Also keep in mind the following examples are on E85.

Adjusting the ignition by 1 degree (earlier spark) while mapping my car on a road, this was a significant difference.

Cooling benefits may vary but on my car at full boost we noticed a max egt of about +800 degrees C (compared to regular fuel 900-1000 C) while pulling through the gears.

Having my car standing the entire winter without starting it, at spring it will hardly be able to start. Change fuel & drive off... Fuel gets "old" & with ethanol this is more noticeable. BUT we are talking an entire winter...say 4-6 months...not weeks.

Rumors also say your fuel lines will get damaged by ethanol. NOT when running E10, thats for sure. How can i say this. Because im running E85 on standard rubber fuel hoses on my race car. The daily driver runs on a mixture.

Aluminum will not corrode because of ethanol & walbro pumps will not brake down.

My car has been standing with E85 since....hmmm...at least 2010, summer & winter, with NO damages what so ever.

BUT!! If you take apart your fuel system make sure you squirt some WD40 (or similar) in to your injectors/fuel pumps, otherwise they might seize up.

So, running several cars on pure E85 & some on a mixture of 15-20% E85 i can say i have had nothing else but benefits.

Running a mixture in our Audi A3 2.0 TFSI quattro saves us money. Up to a certain mixture the car can still adjust timing to keep it unnoticed but since E85 is cheaper...we get the same mileage but save money. Too much E85 & the car cuts boost.

Race cars properly re-mapped on E85 make more horse power compared to running on VP race fuels that cost 5 times more.
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Old 06-10-2015, 10:37 PM
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BTW, O2 means two oxygen molecules. Ethanol has one.
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Old 06-11-2015, 04:52 AM
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Quote:
Originally Posted by scarceller View Post
. . .

Often folks think that you run very rich with ethanol (7.0-9.0 AFR) but the truth is this is because some of the O2 is baked into the fuel.

In summary: a given motor running on E85 vs standard Gasoline will generally develop more torque and HP on E85 the gains can be substantial, from 10-20% HP gains! You will not get great MPG but you certainly will get more power. And you will also need to flow about 20% more fuel at any given engine condition.

. . .
The difference between AFR for alcohol and gasoline isn't because of the single oxygen molecule that is already bound into it. Because that oxygen is already bound into it means that there is no chemical energy to be gathered by binding to it. In essence it is "already burnt" (oxidized).

The real reason for the difference is the difference in the quantity of BTUs that are contained in the molecule. The thermal energy is formed by oxygen binding to the hydrogen and carbon atoms. There is a lot more hydrogen and carbon in gasoline so it offers a lot more in the way of ability to bind oxygen. In other words: Less fuel needed to use the oxygen available in the air.

Alcohol has a higher octane which is simply: It takes a higher quantity of pressure and/or temperature to light it off. (It is harder to get started burning) The first immediate knee-jerk response is, "Harder to burn = Bad" which is wrong as it is more complicated then that. Harder to light off (higher octane) means you can run more ignition lead and higher compression ratios which allows for a more efficient use of the available heat energy.

If you were only going to run alcohol you could run compression ratios more in the range of 13.5:1 or even 14:1 which increases the efficiency of how much of the heat produced can be converted to actual engine output. (Read up on the "Otto cycle" as it explains this plus how diesels are so efficient with their ultra high compression ratios.)

-----------
To get back to the original question...
- Unless a car's systems were specifically designed to deal with alcohol then any alcohol in the fuel is a bad idea.
- Any more octane then is required to run an engine without detonation is wasted unless the engine management system has knock sensors that allow it to dynamically re-tune to take advantage of the extra octane.

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Old 06-12-2015, 02:18 PM
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