Octane question

[beanlover]

I have a place near me that sells ethanol-free fuel...it's expensive ($4.99 a gallon) but I wanted to try it as I had heard some good things from other folks running e-free gas in their Bugs.

I put some in last night...but noticed that it is rated at 91 octane. I know the owners manual states "91 Octane" but that's an old method of calculating as I understand it and that basically translates to our current, normal, 87 octane gas. I'm assuming the "91" on the pump is calculated by current methods.

I don't know much about octane and the reasons for different levels other than I have heard that higher compression cylinders require higher octane to prevent pre-detonation (knocking). I have a stock 1600 so I doubt the compression is high enough to warrant needing any more than 87. Question is...will 91 octane fuel actually negate any "goodness" I might gain by it being ethanol-free? Does that difference in octane cause a difference in the engine dynamics that would affect timing and performance or anything like that?

I don't mind paying more for pure gas but if the octane being higher is going to cause issues I'll just stick with "normal" gas.

There's another place a bit further away that I will check to see if their e-free gas is a lower octane...maybe it won't matter if that's the case...but I thought I'd ask.

[Matt Wilson]

You can probably do a little googling on the subject but there was the old R+M rating and the RON rating for octane. So the old 91 (R+M) measurement method can mislead folks used to only looking at the "91" or "85". Good read here:

https://www.torquecars.com/articles/fuel-octane-ratings.php

Unless your engine is special high compression setup, regular pump gas is probably fine. I know some folks worry about ethanol, but if you drive the car a lot it's probably not a huge issue. if the car sits for long stretches, running the 'clear gas' is sometimes peace of mind that the fuel won't foul up the system while the car is in storage. We have a lot around here for folks with small engines for mowers and saws and boats, who want to leave the small engine in storage and not worry about water in the system.

I've done it all ways - in dry climate, wet climate, cheap gas, fancy gas, long storage periods or running 2 tanks a week through...whatever - it doesn't seem to make much noticeable difference in my opinion. Other folks might feel different.
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1972 Standard Beetle
1969 Baja Beetle

[beanlover]

Thanks for the reply Matt

My engine definitely isn't a high compression set up. I guess I'm more wondering if higher octane is detrimental for lower compression engines or if it just doesn't matter. Jury is still out on e-free vs "normal" gas...hence my experiment...just trying to eliminate a potential variable that would cause unwanted issues...not sure if lower octane "pure gas" is even available near enough to me to warrant making special trips.

[nbvolks]

There's a place up in NH near our mountain house that sells 91 octane ethanol free gas, which funny enough, also sells for $4.99/gallon. I put some in the one time I took the Beetle up there. I have a completely stock 1600cc setup with all the original and functioning, California emissions equipment. I noticed no performance benefit from the fuel, but didn't really expect to. The real benefit with ethanol free gas is that it doesn't absorb water as readily. That's why most ethanol free gas is sold at or around lakes and waterfronts. People use it for boats.

It shouldn't be an issue if you're regularly driving the car and burning the fuel, or if you store the car with as much fuel as you can cram in, and of course a climate controlled space is even better so that you're not getting constant condensation from temperature fluctuations.

[beanlover]

Great info...and makes total sense...I wasn't aware of the water absorption issue with ethanol.

My car is a daily driver right now so it gets driven...almost daily! I'll stick to cheaper stuff with this information in mind. I knew there wouldn't be any performance improvement...was more looking for a "smoothing" of driving experience but I think my issues in that area are still yet to be determined.

Thanks again guys!

[Jimbug57]

The ethanol in gas causes the rubber components in your fuel system to disintegrate. IMHO, you should run ethanol free gas if possible. If you're unable to, for whatever reason, than you should be adding StaBil 360 or similar to your tank to help mitigate the effects of the ethanol.
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Repeat after me "I am smarter than metal!"

[Tim Donahoe]

I’ve owned my Bug since 2012, and put nothing in it but ethanol/gas regular fuel.

No problems.

High octane fuel burns slower, by the way.

Tim
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Richard O'Brien

[Zundfolge1432]

https://www.bellperformance.com/blog/the-major-differences-between-ethanol-and-gasoline

https://en.wikipedia.org/wiki/Ethanol_fuel

[Multi69s]

Since this started as an octane question, I will just go with that. Your engine just needs enough octane to keep from knocking pinging, etc. Octane does not give your engine extra power, it allows you to increase the tune of the engine (higher compression more advance), then it will make more power. So when you buy gas that has more octane then you need, you are just throwing money away. In extreme cases, too much can make your engine lose power. Since gas with a high octane burns slower than low octane gas. This can lead to an incomplete burn.
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[Igpoe]

Ethanol serves no purpose in an automobile. Those who profit from it's use will try to convince you otherwise.
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'73 super.

[KTPhil]

Octane additives and ethanol are less energy dense than "pure" gasoline, and so using them means less power per unit of fuel.

However, some older cars run better on slightly higher octane gas, so there is a "sweet spot" of octane or other additives for any given engine.

My stock '67 used to get better mpg on premium back in the day when gas was really shitty (late '70s), sp despite the lower energy content and higher price, it was worth it. But that was an unusual case.

Use top tier gas of the lowest octane your car runs well on, and don't look back.

I add a bottle of Techron every six months or so to reduce deposits.

[sb001]

Ahhhh, the perfect solution:

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1969 autostick sedan, family owned since new
1600 SP engine
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[creative native]

I have heard for years that ethanol will degrade the rubber linings of a fuel system and so, I've been using non-ethanol premium for many years. I can say I've never had a fuel related issue on a vehicle.

[Starbucket]

The cure for ethanol in the gas when you store whatever is to add "Sta-Bil 360" it prevents Ethanol damage unlike regular Sta-Bil.

[DC0046]

I am a noob with a 2074 Stroker. Run real gas, 91 octane, and octane booster or it runs hot. I know there are many possible reasons for that, IE lean, timing etc. but think its dialed in so run the high octane. Didn’t build the engine so dont know the compression.

[Matt Wilson]

Modern rubber that is rated for fuel should work totally fine with pump gas. if you are having problems, you need to get new fuel lines of recent manufacture that are rated for fuel.

Octane is also a stability rating of the fuel. The fuel's octane will degrade over time, which again, is why for long-term/keep the system water-free storage, it is preferred to have clear gas. For regular driving you should probably use the lowest octane your car is rated to use.

Ethanol is hydroscopic, meaning it will absorb water, so if allowed to sit in wet/humid areas, that's when you worry about it, but for daily driving, not really an issue. In fact, it may help move water through the system.

I've heard of some folks having issues with ethanol fuel giving fuel injection false readings, since it burns a little cooler than gasoline, which gives a false signal back to the computer. Nothing I'd personally worry about.

I'm not that old...but I remember growing up there was a station nearby that still sold leaded fuel... in the 90's...? Now I live near water and the station sells 'clear', which I'd never seen before - but again for boats and small engines people use it. Living in high altitude we had 85/87/91, now at low altitude we have 87/89/93.
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1972 Standard Beetle
1969 Baja Beetle

[Zundfolge1432]

[sb001]

[Floating VW]

[viiking]

Sorry there is so much misinformation here.

The facts:

1. The original measure of octane rating the Raw Octane Number or RON is the proportion of octane versus heptane in a fuel. Octane is an eight carbon molecule straight chain hydrocarbon. Heptane only has 7 carbon atoms. Other straight chain similar molecules include propane (3 carbons) and butane (4 carbons). As a generalisation the more carbon atoms in the straight chain the more bang in the engine. Indeed many cars in the world run and continue to run successfully on propane or butane with limited engine modification!

So the RON was determined by running a "standardised" engine of known capacity, temperature and compression ratio. The engine was started at 100% octane, and heptane (a lower powerful fuel) was slowly added. When the engine started to "ping" under load conditions the proportion of octane to heptane was measured. Let's say this was a generally normal fuel of say 87 Octane i.e. 87% Octane and 13% Heptane.

This measure gave the Octane rating and fuels which contained all sorts of other additives were given an octane rating based on a comparison to the octane/heptane ratio in the standardised engine.

2. Ethanol is NOT a straight chain molecule like octane. It is NOT less energy dense. It has an octane rating of 113. Any proportion of ethanol added will increase the octane rating and hence the potential performance of the engine. The reason that ethanol is used in fuel is that there are only 2 carbon atoms in ethanol for a fuel with higher performance than standard fuel hence there are only 2 carbon dioxide molecules produced in the exhaust (read climate change) versus normal fuels which contain many more carbon atoms.

Yes ethanol does serve a purpose. It reduces pollution. Oil based fuels are an exhaustable resource. Ethanol is not. There is an incentive for the big oil companies to continue to push their product.

Another chemical that some people have heard of is methanol used in drag cars. These produce a lot of energy as well. Methanol is identical to ethanol except it only has ONE carbon atom.

3, Yes ethanol is HYGROSCOPIC not hydroscopic. It is like brake fluid. Only in the worst case and over extended period of times will free water exist. In fact in the "old days" a bottle of denatured alcohol (ethanol) was added into a fuel tank if there was any thought of water being in the tank. The ethanol would absorb the water and burn through over the tankful of gas.

4. Ethanol fuels can degrade some rubber parts. We are dealing with cars that are over 50 years old. Technology has moved on from there. Move to modern rubber parts.

5. Ethanol based fuels are not "thicker" than normal fuel. The viscosity difference is so insignificant that it is unlikely that there is any real difference in how they pull through the jets. Temperature and atmospheric pressure has a much larger impact.

6. Fuels are different from different suppliers.

Fuels are different in different parts of the country.

Fuels used in cold winter climates are blended to make starting easier.

Fuels used in hot climates are purposely made "heavier" to prevent vapor locking.

Storing fuels from one season to the next is problematic as the mixture may be different which actually exacerbates the problem.

Fuels contain all sorts of garbage in them so long as they can meet the specifications, specific gravity and octane rating. The more crap and unsaleable byproducts that a producer can add into their fuel, the more there profit level goes up.

7. Fuel properties change with altitude and temperature. Tuning at one elevation or temperature will affect the performance if the cars are used in another environment. Fuel injected cars take all of this into account but not our 90 year old carburettor technology.

8. A car can be made to run successfully on any sort of fuel (within reason). 100% ethanol cars are available. Cars used to run on town gas during WW2 in countries that had little spare fuel. Cars currently run on LPG and NG. The problem is that the average VW owner does not have the skills to make them do so.
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