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Discussion Starter #1
Greywolf in another thread you said higher octane effectively retards timing. you have any good links that go into detail? I know a chemist told me that different grades of gas are 'chemically identical'. I've never been able to find a decent explanation of the differences, other than that you need higher compression to take advantage of higher octane. I never heard before that it would be detrimental, i'm intrigued.
 

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Octane ratings determine an engine's resistance to detonation. Higher octane gas is harder to ignite than lower octane gas. This normally slows flame front speed. If an engine is rated to use a certain octane number, use it. Higher octane will provide less energy and throw off timing on fixed timing engines.

Many FI systems have knock sensors which retard timing when knocking is detected. This would allow a high compression engine rated for higher octane gas to use a lower octane without damage while sacrificing performance.

You can do a search for more information. Basically, use the octane rating the manual suggests. Too low can cause damaging detonation. Too high wastes money and gives poorer performance. I've read many reports in motorcycle forums where people running higher octane than recommended have idle problems and lower fuel mileage.

What is important for long term reliability and fuel system cleanliness is to use a top tier gas of the recommended octane. http://www.toptiergas.com/
 

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greywolf,

Very nicely stated!

Higher octane fuels do contain more energy potential than lower octane fuels. However the engine must be properly tuned to take advantage of the additional energy potential. On some vehicles, the engine management system will advance the timing even further than normal if it does not sense detonation. This type of system can take advantage of a higher octane fuel. I do not believe the engine management system on the V-Strom is set up to do this.

An interesting side note: Many years ago, I worked on a crew for a C/Fuel NHRA dragster team. We used a small block Chevy as the engine. When the engine ran a mixture of ethanol and nitromethane, and depending on the percentage of nitromethane we ran, the timing was set at 56 degrees BTDC or higher. Slightly different from the typical 8 to 10 degrees advance put into a motor running high octane gasoline! We were also running 14 to 1 compression in that motor. It was built to use the energy available in the fuel.

Good topic!
 

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It's not that the higher octane contains more energy, but that more fuel and air per cc can be safely packed into the combustion chamber on high compression engines. Things like chamber shape, spark timing, mixture swirl and flow, and spark position also effect how high an octane is required to avoid detonation. Alcohol contains significantly less energy than gasoline but is very resistant to detonation and often used in race engines desiged to put a lot more fuel into each cc of the combustion chamber. The bottom line is to use the octane recommended in the manual. When I bought my bike, the setup guy told me to use premium. Many people think it's better gas just because of the name. It isn't better. It's different. Some brands do have better additive packages in their premium blends. Stick to top tier brands as their lower octane fuels have just as good an additive package.
 

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Discussion Starter #5
damn good info, now it makes sense that higher performance fuel isn't as volatile. when i was new a guy i was working with in the Navy threw his cig in the bilge which was half full of jp-5 just to freak me out.

Thanks for the top tier gas link.
 

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I had a fit watching Die Hard II when Bruce lit the jet fuel leak and the fire climbed through the air to explode the plane. The stuff has to be atomized to burn. TV and movies are packed with bad science that people think is true.
 

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greywolf said:
I had a fit watching Die Hard II when Bruce lit the jet fuel leak and the fire climbed through the air to explode the plane. The stuff has to be atomized to burn. TV and movies are packed with bad science that people think is true.

Hey, they call it "Entertainment" and that is what it is. Even the "factual" respresentations are not technically correct.

I saw a demonstration one day - a person had a wrecked car and he was shooting the gas tank with a .50 caliber round. About the only way he could get the gas to ignite was to put a very large flame on the side of the vehicle and shot the gas tank so the round would cause the gasoline to be atomized over the flame.

One of my favorites is "Tombstone" when Doc Holiday fires 3 rounds, in rapid fire succession from a double-barrel shotgun without reloading. Or when he fires a total of 21 rounds from the pair of six guns he is carrying!

Hollywood - can make things quite "Entertaining"!
 

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FL

You don't think gas will ignite, pour about two gallons on the ground, stand real close and toss a lit match into it. Keep it liquid and it is harder to ignite but will if provoked enough. Put it in liquid form in a small can, barrel or what ever and you can light the top and have a nice fire, just don't kick the can or barrel over.

Wolf
It will burn and can be lit with a match, if you atomize it, it can and will explode. but you are right it will not react like the movie depicts.

High octane verses low octane. The high octane fuel has a additive package that allows it to burn at a controled rate, where as the low octane fuel will explode and cause detonation in a high compression engine. One big problem with high octane gas station fuel is that fewer people buy it and it deteriorates in quality. The 87 octane fuel is moved more rapidly so is almost always fresher.
 

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Jet fuel is very much like kerosene. Throw a match into a container full and it will put out the match. Hold a match to it at the surface until the heat causes evaporation and it will ignite the vapors which will in turn vaporize more fuel etc. It works much better atomized or poured over an area so that much of its surface is exposed to air. As you say though, much differently than the Die Hard II model.
 
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