93 Octane or 87 Octane?
- Thread starter TonyM
- Start date
flatheadmurre
Well-known member
Higher octane then you need is a waste of money but not going to hurt anything.
It´s all the non gasoline stuff in the fuel that is no good today.
It´s all the non gasoline stuff in the fuel that is no good today.
Last edited:
Kube
Super Moderator
There is no reason to use it unless your flathead is really "built".
Anything (octane) more than what is necessary is a waste of $$$.
Kube
Super Moderator
Well, ya heard wrong. If a particular area requires an ethanol additive, it's in there regardless of octane rating.
There is a race track (drag strip) near here and at one local station "racing fuel" can be purchased. It does not have ethanol added to it. Of course, it is around $5 / gallon
Tony, in each case I think you have to do your local research.
Out here the highest octane gas is the leaded 100 octane aviation fuel. (not legal on the road because we pay road tax when buying fuel)
The next highest and road legal is a 98 octane ethanol blend. then there are fuels that run around 95 octane, high in aromatics, but no ethanol (my choice) the lowest octane rating available here is 91 and is the most used fuel here. Interestingly the handbooks for my various two stroke implements (world famous and orange coloured) suggest using the higher octane fuel (95) because it has less impurities in it.
These variations come from locally blended and imported fuels (international companies and local companies)
Of course your local fuel suppliers will deliver an entirely different set of specs to the market.
Essentially the Octane rating is the "anti knock" value of the fuel.
My understanding is that a high octane rating means the fuel burns slower. (the flame front travels slower from the point of ignition through the fuel mix in the combustion chamber) This is of little consequence in a flattie that was built to use fuel of about 68 octane and had a compression ratio of about 6:1. Today's fuel has you well covered here.
In a High compression engine say 11:1 the conditions are such that the flame front will travel through the fuel air mix so fast that it would cause catastrophic damage. The "anti knock" additive in the fuel stops this. The "anti knock" additive translates into the Octane rating.
My disclaimer: You should try to stick with one spec (of fuel) and adjust your timing (vacuum brake) accordingly. (You probably wouldn't notice the difference)
Out here the highest octane gas is the leaded 100 octane aviation fuel. (not legal on the road because we pay road tax when buying fuel)
The next highest and road legal is a 98 octane ethanol blend. then there are fuels that run around 95 octane, high in aromatics, but no ethanol (my choice) the lowest octane rating available here is 91 and is the most used fuel here. Interestingly the handbooks for my various two stroke implements (world famous and orange coloured) suggest using the higher octane fuel (95) because it has less impurities in it.
These variations come from locally blended and imported fuels (international companies and local companies)
Of course your local fuel suppliers will deliver an entirely different set of specs to the market.
Essentially the Octane rating is the "anti knock" value of the fuel.
My understanding is that a high octane rating means the fuel burns slower. (the flame front travels slower from the point of ignition through the fuel mix in the combustion chamber) This is of little consequence in a flattie that was built to use fuel of about 68 octane and had a compression ratio of about 6:1. Today's fuel has you well covered here.
In a High compression engine say 11:1 the conditions are such that the flame front will travel through the fuel air mix so fast that it would cause catastrophic damage. The "anti knock" additive in the fuel stops this. The "anti knock" additive translates into the Octane rating.
My disclaimer: You should try to stick with one spec (of fuel) and adjust your timing (vacuum brake) accordingly. (You probably wouldn't notice the difference)
Last edited:
Drbrown
Well-known member
I obtained a carb and mechanical pump rebuilt with components that avoid the problems associated with ethanol gas. My engine is a stock 59AB and starts/runs very nicely on 87 octane ethanol gas. Here we currently pay 2.21 per gallon for that. 91 octane non-ethanol is available but costs about 80 to 90 cents more per gallon, AND one has to drive a half hour each way to get it.
Scott H in Wheaton
Well-known member
Tony,
I highly suggest you find non-ethanol gas if you can. I don't drive my old cars often, or very far, so a few 5-gallon jugs of the good stuff is all I need. Occasionally I drive to Peru,IL for work and I fill up my gas cans with non-ethanol.
the website below lists stations in IL where you can get alcohol-free gas. I see there is a listing in Decatur, maybe not too far from you
http://www.pure-gas.org/index.jsp?stateprov=IL
I highly suggest you find non-ethanol gas if you can. I don't drive my old cars often, or very far, so a few 5-gallon jugs of the good stuff is all I need. Occasionally I drive to Peru,IL for work and I fill up my gas cans with non-ethanol.
the website below lists stations in IL where you can get alcohol-free gas. I see there is a listing in Decatur, maybe not too far from you
http://www.pure-gas.org/index.jsp?stateprov=IL
flatjack9
Well-known member
Actually octane is a hydrocarbon that is blended into fuel to prevent it from auto igniting. It's use maintains an orderly flame front across the combustion chamber. The octane rating is used to rate the performance of the particular fuel being used.
RobR'35
Well-known member
Well I'll say this Kube.
Most gas stations in and around where I live state that on there gas pumps 93 oct. 99 out of 100 times is ethanol free.
I truely believe it's not needed in our fuel.
I've spoke with guys that have worked on old cars longer than I've been living. They've said they've changed out more gas tanks on these old cars since the new use of ethanol in the fuel than ever before.
To me that says something. Fuel lines,rubber hoses,rubber diaphragm,fuel pump valves etc.
Most gas stations in and around where I live state that on there gas pumps 93 oct. 99 out of 100 times is ethanol free.
I truely believe it's not needed in our fuel.
I've spoke with guys that have worked on old cars longer than I've been living. They've said they've changed out more gas tanks on these old cars since the new use of ethanol in the fuel than ever before.
To me that says something. Fuel lines,rubber hoses,rubber diaphragm,fuel pump valves etc.
TonyM
Well-known member
Thanks Scott. Peru is right down the road a bit. A straight shot down I-80.
Kube
Super Moderator
I can't argue with you about the "need" for ethanol blended fuels. It seems the cons of ethanol far outweigh the pros. Unless that is if you are a supplier of corn.
If your area allows ethanol free fuel, great, I'd use it myself. I know in some highly rural farm areas such fuel is available. In the metropolitan areas, it is restricted regardless of octane. The only exception that I am aware of is racing fuel.