Octane and ethanol

[captndan]

We know that ethanol in gas used in old cars is not a good thing. The non-corn gas around here is 90 or 93 octane. This of course is much higher than Henry designed his cars for. What damage if any is this high octane doing to my cars?

[Matt Harwood]

The octane won't hurt anything, but I've found that old cars run better on the cheap stuff, ethanol or no ethanol. The low-voltage ignition systems used in early cars struggle to ignite even 87 octane (my 1941 Buick owner's manual says to use 71 octane for best results), so the high-octane stuff makes it even harder, and it often seems that the car is running rich even when it's not, simply because of incomplete combustion.

 

In short, you're not doing any harm, but I bet the car will run better on low-octane stuff. If you don't store it for long periods with ethanol in it, you probably won't see and deleterious effects from its presence. And if you've rebuilt the carburetor and/or replaced fuel lines within the past, oh, 10 years or so, you probably already have ethanol-resistant materials installed.

[Guest]

The octane won't hurt anything, but I've found that old cars run better on the cheap stuff, ethanol or no ethanol. The low-voltage ignition systems used in early cars struggle to ignite even 87 octane (my 1941 Buick owner's manual says to use 71 octane for best results), so the high-octane stuff makes it even harder, and it often seems that the car is running rich even when it's not, simply because of incomplete combustion.

 

In short, you're not doing any harm, but I bet the car will run better on low-octane stuff. If you don't store it for long periods with ethanol in it, you probably won't see and deleterious effects from its presence. And if you've rebuilt the carburetor and/or replaced fuel lines within the past, oh, 10 years or so, you probably already have ethanol-resistant materials installed.

You should know you can't compare your old Buicks owners manual fuel requirement number with new fuel. There is a difference between Research octane of yesterday and pump octane of today.

[Vila]

Captndan, what is your definition of an old car?

 

When the gas companies started putting ethanol in the gas I ran a tank or two in my 1933 Chevrolet and it ran terrible.  

 

The car would get vapor lock since it is my understanding from other posts on the forum that the alcohol vaporizes at a lower temperatures than normal gas.

 

I switched to 91 octane ethanol free gas and have not had any problems since.

 

I guess it depends on the car, so it may be worth a try.

[padgett]

And how efficiently you want it to run. Problem with premium in an old car (and harder when computer controlled) is that the high-test burns slower than regular and 87 PON (about 91-92 Research) burns slower than 71 octane. Slower burn needs more advance. Lower compression needs more advance (flame propagation rate varies with compression pressure).

Bottom line: throw out the service manual and tune by ear (advance to ping and back off a few degrees). Better than any timing light.

ps pure ethanol is about 110 octane but the heat of combustion is about 1/2 gasoline so you need to open up the jets. Race cars used to run on alky. Bad part was that it burned clear so you could be on fire and not know it.

Edited February 8, 2016 by padgett (see edit history)

[Hupp36]

I  would rather see  them  make  corn whiskey,  Maybe the  government  will  start given  out  food  instead  of EBT credit  cards.

[Matt Harwood]

You should know you can't compare your old Buicks owners manual fuel requirement number with new fuel. There is a difference between Research octane of yesterday and pump octane of today.

 

 

Correct--sort of. Today's octane ratings are derived by taking the average of the Research and Method versions of determining octane ratings (R+M/2, it says so right on the pump). In 1941, they used the Research method almost exclusively which tended to make octane ratings slightly higher than they actually were, which is why we now average the ways of determining octane. That said, I don't think there's any chance that somehow they were running 90 octane in the 1940s and my advice still stands. Octane is octane.

 

Octane is a measurement if a fuel's resistance to ignition, and 6-volt electrical systems will have an easier time with lower octane fuels, regardless of what method is used to determine the actual number. The resultant incomplete combustion will masquerade as an overly rich condition, which is why a lot of old cars end up being tuned too lean on today's fuels. That wasn't part of his question, but it's a factor. Old cars will typically run best on the cheapest gas you can find, ethanol or not. Ethanol's problems, of course, come from the way it attacks rubber components in a fuel system, which is a totally different argument with valid concerns, but again, as I said, if you're running it regularly, ethanol probably won't cause any lasting damage but I might recommend the non-ethanol gas, regardless of octane, for long-term storage purposes such as over the winter.

 

Are we done being pedantic?

Edited February 8, 2016 by Matt Harwood (see edit history)

[DavidMc]

My experience is confined to cars of the 1920's with very low compression ratings. Octane rating is irrelevant, they run fine on any of the available fuels and in fact run just as well on an additional  10-20% Kerosene plus gas.

 

However I have found that any fuel containing ethanol will vapourise in hot weather more readily that any non ethanol fuel.

 

Adding the kerosene reduces vapou r lock but here in Australia in hot weather (35-40 C) on a long climb my cars will vapour lock  no matter what fuel, if driven  hard.  I suspect 100% kerosene would avoid this.

 

But ambient conditions play a much greater role in performance than fuel,  Under very cold ( say 5-10 deg C) damp conditions my cars perform best.

 

If your climate does not cause vapour lock my experience (1920's cars only) is that any fuel is fine.

 

There is no science to these comments, just experience driving three different 1920's Packard over many years.

[carbking]

We have had many potential customers call with "carburetor" problems, specifically rough idle and less power than they expect.

 

Questioning often acquires the answer "I always put premium fuel in all my cars".

 

There is much written on the internet concerning octane ratings, energy content of various fuels, etc. I spent a lot of time researching, and attempted to boil it down for the following article, which attempts to aid the enthusiast in the selection of the correct octane for their vehicle:

 

http://www.thecarburetorshop.com/Octane.htm

 

In a nutshell, I doubt very seriously if there are any stock engines for production cars built before the horsepower wars of the mid-1950's that will benefit from the use of premium fuel.

 

There used to be a "rule of thumb" that the octane required should be 10 times the compression ratio; but that was when RON was being used, thus no longer applicable using AKI.

 

Jon.

Edited February 8, 2016 by carbking (see edit history)

[carbking]

My experience is confined to cars of the 1920's with very low compression ratings. Octane rating is irrelevant, they run fine on any of the available fuels and in fact run just as well on an additional  10-20% Kerosene plus gas.

 

However I have found that any fuel containing ethanol will vapourise in hot weather more readily that any non ethanol fuel.

 

Adding the kerosene reduces vapou r lock but here in Australia in hot weather (35-40 C) on a long climb my cars will vapour lock  no matter what fuel, if driven  hard.  I suspect 100% kerosene would avoid this.

 

But ambient conditions play a much greater role in performance than fuel,  Under very cold ( say 5-10 deg C) damp conditions my cars perform best.

 

If your climate does not cause vapour lock my experience (1920's cars only) is that any fuel is fine.

 

There is no science to these comments, just experience driving three different 1920's Packard over many years.

 

David - you may be correct about running very well on 100 percent kerosene, but I doubt you would enjoy attempting to start the engine when cold.

 

Many tractors (lower compression engines) were sold to use distillate or kerosene, but had an auxiliary tank for gasoline for starting. Once the engine was warmed to normal operating temperature, the fuel was switched to the main kerosene or distillate tank.

 

Jon.

Edited February 8, 2016 by carbking (see edit history)

[Guest]

Correct--sort of. Today's octane ratings are derived by taking the average of the Research and Method versions of determining octane ratings (R+M/2, it says so right on the pump). In 1941, they used the Research method almost exclusively which tended to make octane ratings slightly higher than they actually were, which is why we now average the ways of determining octane. That said, I don't think there's any chance that somehow they were running 90 octane in the 1940s and my advice still stands. Octane is octane.

 

Octane is a measurement if a fuel's resistance to ignition, and 6-volt electrical systems will have an easier time with lower octane fuels, regardless of what method is used to determine the actual number. The resultant incomplete combustion will masquerade as an overly rich condition, which is why a lot of old cars end up being tuned too lean on today's fuels. That wasn't part of his question, but it's a factor. Old cars will typically run best on the cheapest gas you can find, ethanol or not. Ethanol's problems, of course, come from the way it attacks rubber components in a fuel system, which is a totally different argument with valid concerns, but again, as I said, if you're running it regularly, ethanol probably won't cause any lasting damage but I might recommend the non-ethanol gas, regardless of octane, for long-term storage purposes such as over the winter.

 

Are we done being pedantic?

We don't do name calling here unless we want a moderator. Want a moderator? You should know they are overly sensitive to these types of things. You made a mistake and I pointed it out. That is not being Pedantic, I didn't spell out anything in any detail to warrant a Pedantic comment ( like you just did above in your explanation comment).

Let's just get on with it and stop trying to make something out of nothing

Edited February 8, 2016 by helfen (see edit history)

[C Carl]

100% kerosene ? NO ! NO ! NO ! I am and have been traveling, and eventually will prepare a response to another topic for which I will have to strap on a bib and munch a slice of humble pie. This will help us all here. More modern distillation curves are from my old Marks Mechanical Engineers Handbook , Sixth Edition (1958). The earlier curves and fascinating info is from 3rd ed. (1930) which came to me just prior to my departure. This will explain the inordinate amount of intake preheat on cars from mid 'teens - late '20s. I expect the 2nd. Ed. (1924) I ordered will beat me home. I will include any relevant info, and also data from Merck Index. In the meantime, block off all exhaust flow preheating intake on your subject period cars. Also interrupt thermal bridging where practical. You will then run far better on modern 87 octane. Sad note to book lovers : Cliff's Books in Pasadena , Ca. was gone when I stopped by a week ago. I had hoped to pick up a Marks First Edition (1916). Might have to order that too , depending on info gleaned from 2nd. Ed. Peace be upon all of you my dear brothers and sisters. - Carl

[Jim Bollman]

Never noticed higher octane being harder to start. I ran 100 LL Av fuel in my 8N 6.5:1 compression for several years when I couldn't get no ethanol fuel and it started easier and seem to pull harder. Also ran it in one of my Crosleys with good results. Since moving I can actually get no ethanol regular here so I am using that in the 8N and it doesn't start as easy again. Still run 100 LL in generator but at $5.95/gal it is nice using less of it but the long shelf life is great for generators.

[Guest Bob Call]

C Carl, and others, if you want technical books try Brown Book Shop in Houston.  brownbookshop.com

 

Technical publications are all they sell. If they don't have it and if it's available they will get it for you.

[padgett]

Gas is gas where btu per pound is concerned, they are all the sameish. Alky (meth) has about 1/2 that of gas. Ethanol about 65%. Diesel/Kerosene have about 10% more than gas & may need preheating. Unless the engine is designed for it I would not try to run a gas engine over about 5:1 compression on kerosene though it might be usable to stretch gas a bit, say one gallon in four or five but only if you really need to.

Octane is about resistance to detonation which has the adjunct of higher octane is slower to burn. How fast it burns is also a function of compression pressure.

 

So to run premium in an older engine, you will probably need more advance than the book says.

If I have a question, I generally go to Obert or Ricardo, have yet to see an improvement on them.