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87 Octane seems to work just fine
- Thread starter vito1943
- Start date
BajaRon
Well-known member
More than you wanted to know about Octane.
I am about to bore you with a long dissertation. So be forewarned.
There are so many misconceptions and myths surrounding Octane. Including what it is and what it does. But at least some of it is understandable. Because higher octane is required in higher output engines, people assume that Octane produces more power when this is actually not true. What higher octane does is allow engineers to build higher output engines without blowing them up.
Gasoline, type for type, quality for quality, will have the same stored energy potential, regardless of octane rating. Ethanol fuel has a lower stored energy component due to ethanol producing less energy than gasoline. Still, the energy potential, apples to apples, will be the same regardless of octane.
Higher compression gives engineers the ability to provide greater power output from the same engine. Other things need to change to take full advantage of this higher compression, but you get the idea. Higher compression creates more heat, because as you compress a gas (Air, fuel mix, etc.) you also heat it up. This is why the pipe going from your shop compressor to the tank gets very hot. This happens with no combustion at all. And your shop compressor is running at a lower compression than your Spyder engine.
A diesel engine runs at much higher compression than a gasoline engine because diesel fuel is very hard to ignite. The increased heat from compression is actually used to fire the fuel with no need of a spark plug. But high compression in a gas engine will fire the fuel as soon as it is injected. And because gasoline is so prone to explosion with heat, it is necessary to control this event with spark ignition from the spark plug. This requires that the gasoline not explode prematurely due to heat above it's ignition point. And this is where octane comes in.
Simply put - octane helps gasoline resist ignition at higher temperatures. The higher the octane, the higher the temperature it can withstand without exploding. And when it does explode, it burns at a slower rate than a lower octane fuel. The same energy is produced, but over a longer length of time. The difference is small on a time scale, but these factors are critical to running a high compression engine at peak efficiency.
Using lower octane fuel than recommended means you need to cool things down or you're going to damage your engine when the gasoline explodes too early. Before computers, that's exactly what happened. But now, your computer retards ignition to accomplish the necessary cooling of the combustion chamber. It does this by having your spark plug fire later than it should. This creates the opposite effect of compression.
Compressing a gas causes heat. Expanding a gas creates cool. That's how your air conditioner works. The compressed freon is pushed through a venturi into a larger space where it instantly cools as it expands. The same principle applies as the piston goes past Top Dead Center and starts it's travel downward. The fuel air mixture begins to expand into the now larger space created by the descending piston and the gas cools. All in an effort to have the gasoline wait for the spark plug to ignite the mixture.
The computer does not detect octane levels. Instead, it watches for the very tiny signs that the fuel mix is beginning to ignite prematurely. It makes instant adjustments before any damage is done.
BRP claims that the computer samples some systems at 20,000 a second. That's pretty good reflexes.
I am about to bore you with a long dissertation. So be forewarned.
There are so many misconceptions and myths surrounding Octane. Including what it is and what it does. But at least some of it is understandable. Because higher octane is required in higher output engines, people assume that Octane produces more power when this is actually not true. What higher octane does is allow engineers to build higher output engines without blowing them up.
Gasoline, type for type, quality for quality, will have the same stored energy potential, regardless of octane rating. Ethanol fuel has a lower stored energy component due to ethanol producing less energy than gasoline. Still, the energy potential, apples to apples, will be the same regardless of octane.
Higher compression gives engineers the ability to provide greater power output from the same engine. Other things need to change to take full advantage of this higher compression, but you get the idea. Higher compression creates more heat, because as you compress a gas (Air, fuel mix, etc.) you also heat it up. This is why the pipe going from your shop compressor to the tank gets very hot. This happens with no combustion at all. And your shop compressor is running at a lower compression than your Spyder engine.
A diesel engine runs at much higher compression than a gasoline engine because diesel fuel is very hard to ignite. The increased heat from compression is actually used to fire the fuel with no need of a spark plug. But high compression in a gas engine will fire the fuel as soon as it is injected. And because gasoline is so prone to explosion with heat, it is necessary to control this event with spark ignition from the spark plug. This requires that the gasoline not explode prematurely due to heat above it's ignition point. And this is where octane comes in.
Simply put - octane helps gasoline resist ignition at higher temperatures. The higher the octane, the higher the temperature it can withstand without exploding. And when it does explode, it burns at a slower rate than a lower octane fuel. The same energy is produced, but over a longer length of time. The difference is small on a time scale, but these factors are critical to running a high compression engine at peak efficiency.
Using lower octane fuel than recommended means you need to cool things down or you're going to damage your engine when the gasoline explodes too early. Before computers, that's exactly what happened. But now, your computer retards ignition to accomplish the necessary cooling of the combustion chamber. It does this by having your spark plug fire later than it should. This creates the opposite effect of compression.
Compressing a gas causes heat. Expanding a gas creates cool. That's how your air conditioner works. The compressed freon is pushed through a venturi into a larger space where it instantly cools as it expands. The same principle applies as the piston goes past Top Dead Center and starts it's travel downward. The fuel air mixture begins to expand into the now larger space created by the descending piston and the gas cools. All in an effort to have the gasoline wait for the spark plug to ignite the mixture.
The computer does not detect octane levels. Instead, it watches for the very tiny signs that the fuel mix is beginning to ignite prematurely. It makes instant adjustments before any damage is done.
BRP claims that the computer samples some systems at 20,000 a second. That's pretty good reflexes.
Last edited:
Redbeard
Active member
Something I do notice when I run 93 octane is this: The 1330 engine in my RT shifts nicer! I don't quite understand why but it is enough for me to continue to run high octane fuel. I check my milage with every fill up (actual milage/gallons used) and there is zero difference between any grades of gasoline I use. I am surprised the comuter estimated milage usually is very close to actual fuel use. Generally within 1 mpg.
safecracker
Well-known member
I ran 87 in my old Spyder (V-Twin) for 96,000 miles and I have 36,000 miles on my 21 Spyder and all she gets is 87. Runs fine and I ride 2 up 95% of the time. Bruce
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