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TrickyNicky

Fuel, Premium vs Regular, Octane, 87, 89, 91, 94 etc

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TrickyNicky

Can the wonderful gearheads of TMC explain the difference between fuels. I'm talking in general, not just specific to our boats, but cars, trucks etc. Just a general discussion, here's some questions to get you started.

1- What are the ratings 87, 89, 91 etc?

2- What is the purpose of Octane, why do I want more or less?

3- Is it bad to run too low octane, what about running too high?

4- Is the cost for higher octane ever offset by increased mileage? Can you break even?

5- Does mileage increase as octane goes up, only?

6- Any particular engine setups where it's more important to run proper octane, N/A, SC, TC?

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CrystalSurf

I don't have answers to any of these questions. However, you should know that 91 octane in Ontario does not contain any ethanol.

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Bobby Light

Those numbers are the octane rating, octane prevents detonation or engine knock. High performance engines require higher octane gas to prevent this detonation. The higher the octane number the slower it burns. Adding higher octane gas to whatever engine you are talking about doesnt necessarily mean you'll have any increased mileage. Engines have different octane requirements your best performance and mileage will be when you use the required octane, using a lower octane gas can have negative results.

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Jimmypooh

higher octane prevents pre-ignition when the gas and air mixture is compressed. If your engine was built with a higher compression in mind you need higher octane. If it was not built with higher compression, then the higher octane is a waist.

That being said, if your engine is computer controlled, the computer generally has sensors that sense pre-ignition and will dial back the timing. When that happens you loose some horse power.

Moral=> If your engine requires higher octane by the manufacturer then use it, otherwise it's a waste of money.

1- What are the ratings 87, 89, 91 etc? Formula basically stating how well it resists ignition due to pressure.

2- What is the purpose of Octane, why do I want more or less? See above

3- Is it bad to run too low octane, what about running too high? Too high does nothing, too low can pre-ignite when not compensated for.

4- Is the cost for higher octane ever offset by increased mileage? Can you break even? Only when the engine is built for higher octane.

5- Does mileage increase as octane goes up, only? only if engine was built for it.

6- Any particular engine setups where it's more important to run proper octane, N/A, SC, TC? High compression engines

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khelfrich

octane is a number relative to the fuels ability to resist pre-detonation, which causes knock

higher octane does not give more performance

the higher compression ratio the higher octane is needed or i will say relative compression ratio for a supercharged/turbocharged engine wile forced induction engines usually have a lover compression ratio the pressures in the cylinder are higher from the higher pressure entering the engine

now you may see a performance gain from higher octane if you were running too low and octane because the ecm (computer) will adjust timing and other parameters if it senses knock and retard the engine to stop the knock thus giving lower performance.

basically just use what is recomended

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MLA

1) Those are the pump octane numbers. These numbers represent the ignition point, or volatility, of the fuel. Lower the octane number, the more volatile, higher the number, the less volatile. More volatile means it takes less heat to ignite, less volatile means it takes more heat to ignite. It has nothing to with its expelled energy or quality. Thats all marketing BS from the manufacturers. Once ignited, they all have about the same BTU's

2)Gasoline is a blend of octane and heptane molecules. The ratio of those two is how the volatility is controlled. The biggest factor in choosing the correct octane level, is the engine compression ration.

3) Running too low of an octane then what your engine requires can lead to pre-ignition. This can lead to piston damage and eventually a catastrophic engine failure. Running a higher octane then whats required, is just spending more money.

4 and 5) higher octane will not improve mileage. Its marketing BS

6) yes! Every engine needs to run the correct, or higher octane. Even a 135 HP 3.0L 4 cyl Merc in a 16ft Bay Liner.

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Soon2BV

The key is to use what is recommended.

While higher octane will not give you better mileage, using too low of an octane causes the computer controls to adjust, and you are less efficient. Less efficient is lower mileage.

It has nothing to do with engine size or power. My son has a mini-cooper that requires 93. High compression engine, My GMC 6.2L requires 87.

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OneCent

lowest you can get at my place is 95

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longbeard

Incase someone was wondering 87 means 87-percent octane and 13-percent heptane, heptane does not handle compression very well. The higher the octane rating, the more octane you are paying for essentially. And as stated before, the more compression it can handle.

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TrickyNicky

Incase someone was wondering 87 means 87-percent octane and 13-percent heptane, heptane does not handle compression very well. The higher the octane rating, the more octane you are paying for essentially. And as stated before, the more compression it can handle.

Can't you get 105 octane?

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nyryan2001

Thermodynamics PV = NRT

As P in pressure goes up as the piston rises and squeezes the fuel air mixture up the T in temp goes up..even before the spark from the plug goes off. That squeeze and compression can raise the T to the point it becomes an early compression ignition.... vs the perfectly timed spark ignition. The T and P required to ignite 87 and move the piston is lower than the T & P for 91.

All of this happens in every cylinder of your engine every RPM in a fraction of a second.

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wakesetter8796

In my mustang is has a 93 race tune. I put 87 in it one time and could definitely tell a difference.

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longbeard

Can't you get 105 octane?

Haven't you heard of giving 110%? No, when the rating reaches 100 it is the gasoline's performance rating, not the percentage of actual octane in the gas

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TrickyNicky

Thermodynamics PV = NRT

As P in pressure goes up as the piston rises and squeezes the fuel air mixture up the T in temp goes up..even before the spark from the plug goes off. That squeeze and compression can raise the T to the point it becomes an early compression ignition.... vs the perfectly timed spark ignition. The T and P required to ignite 87 and move the piston is lower than the T & P for 91.

All of this happens in every cylinder of your engine every RPM in a fraction of a second.

That actually explained a lot. Thanks for taking me back to thermo. Keep in mind as P goes up that V is going down.

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brad72

My wifes car specifies 98 octane fuel and has never run on anything less. We always run 91 or 95 in the boat. In some gas stations 95 is the lowest available unless you use a ethanol based fuel which I won't use so the choice is simple unless I want to use premium 98 which is really a waste of money.

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Bobby Light

Can't you get 105 octane?

It's called Avgas

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wakesetter8796

My wifes car specifies 98 octane fuel and has never run on anything less. We always run 91 or 95 in the boat. In some gas stations 95 is the lowest available unless you use a ethanol based fuel which I won't use so the choice is simple unless I want to use premium 98 which is really a waste of money.

What car does she have?

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Bawshogg

Crazy difference in fuel quality for those down under huh?

I have personally used 117 octane from VP back in the day. Smells sooooo good.

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brad72

What car does she have?

2005 Mazda 3 SP23.

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wakesetter8796

Wow never heard of requiring 98

Sent from my iPhone using Tapatalk

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saskicker32

It's called Avgas

Avgas is 100 octane (usually), I mean technically it just stands fro aviation gas. It is also LL (low lead...usually), thats why the EPA hates us general aviation guys

Edited by saskicker32

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gorilla

Wow never heard of requiring 98

Sent from my iPhone using Tapatalk

That's because they use RON instead of AKI ratings. If i remember right, 98 RON is about 93 AKI (the designation that we use in the states). RON is roughly 5 points higher than AKI.

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wakesetter8796

Hmm interesting. The japs all do that?

Sent from my iPhone using Tapatalk

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