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Hello what fuel should I put in my 1926 dodge the mechanic put high octane( the expensive gas) and says u should put a lead additive. My friends run cheap low octane has with marvel mystery oil. What would you recommend for this daily driver.

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Gasoline in the mid '20s would probably have been in the 40 something octane range. Perfect for cars with compression ratios of 4.something. You need octane as low as you can get. These cars would have had better performance and burn cleaner than they do today. Kerosene ( diesel and jet fuel ) is about 140 octane. It is not the solution. I don't know a way to safely and economically lower the octane of gasoline. Octane rating refers to flame front propagation rate at standard conditions. With higher compression pressure , high octane provides a slower flame front propagation rate to compensate. With our low compression pressures , we would benefit from lower octane to speed up the combustion. We could then extract more B.T.U.s from the fuel , and have combustion be more complete when the exhaust valves open. Old pilots who received their flight engineers training 40 - 50 - 60 years ago in the days of recips learned this well. Gasoline in extreme altitude areas of the world is refined to 70 something in order to give engines enough power to pull grades there. In mountain areas of the U.S. , octane is a bit lower than it is at sea level. I sure wish I could get 50 octane for my '24 and '27 Cadillacs. I put few enough miles on them that I would be willing to pay much more for it. I think octane up to 127 is available in the Los Angeles , Ca. region . Very expensive. 13:1 compression high performance cars love that. Specialty gasoline. Yeah , we need some lower octane for or old cars. Any ideas ? - Carl

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I talked to a guy who had a 26 Dodge and he said he had to put oil in the fuel. At first he ran his on straight pump fuel and he claims he seized the engine. After an expensive rebuild he always added oil to the gas. How much is anyone's guess.

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Here is an interesting post on Kerosene and Diesel in Gas engines.

http://www.smokstak.com/library/technical-information-7/running-kerosene-in-a-gasoline-engine-23/

BLUNTLY : A LOT OF MISINFORMATION HERE. F.Y.I. : diesel and jet fuel are basically kerosene with appropriate additives. 140 OCTANE. Go hang out at an airport and smell the kerosene exhaust from the jets. While there , find an old pilot who might have flown aircraft with R2800s or R3350s or studied them in flight engineers school long ago. Ask him about anti-detonation injection ( don't get fooled by the 50/50 mix of alcohol and water - alcohol was just antifreeze for cold temps encountered in flight ) , and 2-speed superchargers. A.D.I. and low blower for take off when manifold pressures were high , high blower for low atmospheric pressure at altitude. No , diesels are compression ignition at 22:1 or 23:1 compression. Diesel fuel ( kerosene ) is around 140 octane. Not 25. Not 87 , not 110 , but 140. That is a SLOWER burn ( that looks like BUM , but should read BURN )'than gasoline. You'll see how fast 92 octane gasoline burns in a diesel if you ever make a mistake at the gas station ! Your mechanic will love you , but shake his head and snicker behind your back ! Your '60s high compression engine will BARELY run on diesel , but not because of compression ignition. You really need those 22 + ratios to accomplish that with 140 octane. I don't really know about very hot kerosene vapor , but I'll leave speculation for later.

Got to run and get out of town for a long Memorial Day weekend. How lucky we are to be old folks in the U.S.A. Most of us have family and/or friends who have died fighting for our freedom we enjoy so much. Profound thanks to them , and may memories of them be preserved forever. Please drive slowly and carefully. - Carl

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This question has been answered dozens of times, some of them very long and technical. If you do a search you should find enough info to keep you amused for hours.

 

First of all no way is kerosene 140 octane. If it was, all race cars would be using it. Kerosene is LOWER in octane than gasoline.

 

This is what you want for a 1926 engine. In those days fuel quality was poor and compression ratios low. Your engine was built to run on low octane fuel with no lead, but lots of kerosene in it.

 

Your car should run fine on the lowest octane regular but may run even better if you add 10% to 25% kerosene or stove oil. Some even add diesel fuel. This also helps prevent vapor lock in hot weather.

 

It can't hurt to use some MMM, Redex, Bardhal or your favorite brand of upper cylinder lubricant. This was another popular trick in the old days to reduce engine wear. It also helps prevent rings and valves from getting stuck on motors that are left sitting for long periods of time.

 

Incidentally if you have a 2 stroke lawn mower you can take the left over gas at the end of the summer and put it in your old car's tank.

Edited by Rusty_OToole (see edit history)
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"First of all no way is kerosene 140 octane. If it was, all race cars would be using it. Kerosene is LOWER in octane than gasoline."

 

On my way out the door : question : do you think the following is true : kerosene, heating oil , no.2 diesel,and jet fuel are all basically the same with different additives ? Also , is this true : old dogs are capable of learning new tricks ?

With greatest admiration and respect , - Carl ( an old dog who's flight engineer training took place a long time ago )

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I did a google search on kerosene octane rating and it came up at about 25. I also read a great paper by a couple of mid-east chemical engineers analyzing the effect on octane rating of adding kerosene to gasoline. Short answer is that a mix of 87 octane gas with 10% kerosene is 81.5 octane (RON). it was pretty much a straight line down at a 45 degree angle for every 2% additional kero. I don't if the line would continue straight but if it did 30% kero would give you about 70.5 octane (RON) That would be about 5 gallons of kerosene in a 16 gallon fill up. wow!!

 

Dave

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In the late 50's I had a high school friend with a 49 or 50 Ford flat head V8.  When we went on a trip of over 100 miles, he would run a mixture of about 3 parts gas to 1 part kerosene.  Gas was $.29 and kerosene was $.10.  It seemed to run good on the highway but smoked a little and some times it was a little hard to start.  I don't remember him ever having engine problems, he probably drove it 30 or 40 thousand miles in 2 years or so.  I lost track of him after high school & he could have driven it through college.

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As has been said this subject has been discussed many times before and  the attached brief article by BP (Petrol =Gas!)  shows how fuel has changed over the years I have posted it before but it is always good for another read.  Apparently the best fuel, that is most like that for which our cars were made, is aviation fuel. This is not much help.

 

http://www.bp.com/content/dam/bp-country/en_au/media/fuel-news/modern-petrol-vintage-engines.pdf

 

The above also makes it clear that octane rating is irrelevant to our old cars.

 

As I see it there are only 3 factors to consider:

 

1)  Volatility or boiling point.  Modern fuels are far more volatile than the fuel used when our cars were new so they are more likely to vapor lock in warm to hot climates.  Octane rating has nothing to do with volatility it simply avoids pre-ignition if you don't have that the octane rating is fine and likely to to be far higher than you need.. High octane ratings are neither detrimental or beneficial.   With low compression ratio any octane fuel is fine. However here in Australia the lower octane fuels have 10% ethanol which   so I chose whatever fuel has low or zero ethatnol regardless of octane simply to avoid the vapor lock problems that the ethanol makes worse.

Avgas would be great if we could get it - planes do not vapor lock - I hope!!

 

2)  Ethanol.  This is well documented on this forum, it affects rubber not designed for ethanol (eg hoses and fuel pump diaphragms) and it increases volatility.  Here in Australia the lower octane fuels have 10% ethanol  so I chose whatever fuel has low or zero ethanol regardless of octane simply to avoid the vapor lock problems that the ethanol makes worse.  In cold weather fuel with ethanol works fine.  My cars, pre 1930 do not have any components that can be damaged by ethanol - please correct me if I am wrong

 

3) Lead.  Lead protects against valve seat recession but it is my understand that for this to happen the cars would need to be driven hard for very high mileages most of us will never do that.   Using an additive is probably unnecessary but for the small cost it might give some peace of mind and possibly provide some cylinder lubrication.  

Many people fit hardened valve seats but this can cause more problems.  On some cars machining out the old seat to take the insert can weaken the block or head , I have a block that is beyond repair because it has cracked around a number of the hardened valve seats..

 

Speaking for my cars  of the 1920's and a 1912 and they all run fine on any available fuel except in hot weather when vapor lock occurs .   Mine will run with as much kerosene as I can add,  it helps to reduce vapor lock (along with heat shields, insulation, electric pumps correct tune etc) none of which prevent the dreaded vapor lock under extremely hot conditions) .   Others have had success in reducing vapor lock with diesel, I tried it once and it made no difference, it is likely nothing would have worked that day because it was so hot.

 

Forget about octane rating it is irrelevant to any low compression car.  They will run fine on any of the octane ratings available and would also run fine on much lower octane fuels if they were available.  I understand that the cars of the 1920's will run fine on 100% kerosene  once they are fully hot but I have not tried that.

 

Contrary opinions welcome!

 

David

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"First of all no way is kerosene 140 octane. If it was, all race cars would be using it. Kerosene is LOWER in octane than gasoline."

 

On my way out the door : question : do you think the following is true : kerosene, heating oil , no.2 diesel,and jet fuel are all basically the same with different additives ? Also , is this true : old dogs are capable of learning new tricks ?

With greatest admiration and respect , - Carl ( an old dog who's flight engineer training took place a long time ago )

 

 

 

 

Of course it is not true. Jet fuel is close to kerosene, aviation gas is close to car gasoline but higher octane among other things. Jet engines and piston engines are completely different. Octane is irrelevant to a jet engine.

 

Octane was adopted as a measure of knock resistance. Too high an octane fuel is unnecessary and even counter productive. The old long stroke low compression engines will actually run better and cooler, and develop more power on low octane fuel than on the highest octane modern gasoline.

Edited by Rusty_OToole (see edit history)
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I was told by an old time mechanic that in the thirties there were 3 grades of gas commonly available. High test, regular, and straight run. The straight run gas was plain, low octane gas with no lead or other additives. He described it as the next thing to kerosene.

 

This cheap 50 octane straight run gas was for donkey engines, garbage trucks, and old jalopies like Model T Fords. But it also worked great in Rolls Royces because they had such low compression engines.

 

He was the one that taught me that too high octane gas was not only unnecessary but counter productive. And that people who bought hi test for cars that required regular, were wasting their money.

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