octane ratings
- Thread starter lot boy
- Start date
jjmetheny
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The higher the octane the more stable the fuel is under heat and pressure, less chance of pre-ignition/detonation. It doesn't mean that it will increase engine temps. Some race fuels will run leaner than pump gas so if your bike was tuned with pump gas and then you run certain race fuels your engine temps can go up from the motor running a little leaner.
i ask this question to settle an argument-- i run 87 in my busa. its my understanding that running high octane gas in a motor that doesnt call for it is a waste of money and can only result in higher engine temps by a few degrees- no power increase ect... race gas is a whole other animal and isnt part of the arguement... any thoughts?
it is a - waste - of money.(lot boy @ Mar. 04 2007,17) i ask this question to settle an argument-- i run 87 in my busa. its my understanding that running high octane gas in a motor that doesnt call for it is a waist of money and can only result in higher engine temps by a few degrees- no power increase ect... race gas is a whole other animal and isnt part of the arguement... any thoughts?
Yes, unless the motor has been built or had performance parts added and setup for a higher octane.
From what I've read unless you're going north of 300 HP the builders still have them running on 87 and you save money. Running higher octane in a stock or close to stock ride would not only cause it to run hotter, but it would be a waste of money at the pump.
I had my bike dynoed with 93 oct, and tried to go to 89 oct and it ran like crap, went back to 93 oct and it ran fine again.
use 87 unless you've tuned your bike to run higher....
cosmo
Registered
FWIW:
According to my good friend who was an engineer for Chevron there are, at last count, 11 different regional formulations for gasoline in the lower 48 not counting seasonal formulations. How each company achieves they're specific octane rating can result in a vastly different compound within that region. In short: An 87 octane CITGO blend may run fine in your stock Oklahoma Busa while a Chevron 87 may run like stink in my stock Norcal Busa. Try em all and stick with what works for you. Mine seems to run most predictably on Unocal/76 91.
Oh and theoretically, the higher octane fuel should have a lower cylinder temperature but no measurable difference in coolant temp. Or so says the engineer.
According to my good friend who was an engineer for Chevron there are, at last count, 11 different regional formulations for gasoline in the lower 48 not counting seasonal formulations. How each company achieves they're specific octane rating can result in a vastly different compound within that region. In short: An 87 octane CITGO blend may run fine in your stock Oklahoma Busa while a Chevron 87 may run like stink in my stock Norcal Busa. Try em all and stick with what works for you. Mine seems to run most predictably on Unocal/76 91.
Oh and theoretically, the higher octane fuel should have a lower cylinder temperature but no measurable difference in coolant temp. Or so says the engineer.
Newmill nailed it. Higher octane pump gas will run cooler cylinder temp. All the different fuel blends and then throw in ethanol in some areas. My bike will run lower ET a the strip when using 92 amoco ultimate compared to 87 octane from the same station. Dyno will prove the same thing.
Go for it
The manual says stay the heck away from alcohol
ibified
Registered
This is a snippit of some information I posted on another website for bikes (VTX Cafe for those of you who are interested - that was what I had previous to my Busa) when someone was trying to tell everyone how much more power and fuel economy they got in their VTX when they ran premium.
Here it is. Keep in mind, I'm just an automotive engineer, so I may not know much about how gasoline octane deviations might change the characteristics of combustion (or precombustion) inside a cylinder.
First, a couple definitions to get out of the way, since this often causes some confusion for folks:
RON: Research Octane Number
MON: Motor Octane Number
What goes into your tank, if you read whats on the label at the pump, is actually neither of these. Fuel from pumps (at least in the US) uses the (R+M)/2 formula, which means that they take an average of the two. Typically, your RON is about 8-10 points higher than your MON is. What this means is that fuel with a RON of 91 is actually going to be equivalent to somewhere between 86 and 87 {(R+M)/2, with R being 8-10 pts higher than M, is going to give a yield between 4 and 5 points down from R} I would guess that the RON posted on the body is for people in Europe and Austrailia, since that's where RON is the "headline" number listed on fuel there.
Octane itself is simply a rating of a fuel's resistance to autoignition. if you want a further explanation of it, read on:
Octane is measured as a relative mixture of isooctane (which is 2,2,4 trimethylpentane, an isomer of octane) and n-heptane. a fuel rated at 93 octane, for example, has a 93% mixture of isooctane to 7% n-heptane. The proportions of that mixture may not be precise, but the resistance to autoignition will be the same as if those were the exact proportions.
I can't give a definitive answer of what runs better, and nobody else can either. At least not for everyone. Ideal octane for a motor is going to vary based on atmospheric pressure, temperature, relative humidity, compression ratio, timing, and numerous other things. The best thing to do is to try each for yourself, check your mileage, and listen to what your butt is telling you. As for fuel mileage, additives are going to play a FAR greater role in fuel mileage than will the octane rating.
Octane, by definition, is the resistance to burn or detonation. The higher the rating, the slower the burn when ignited during the compression burn cycle of the piston.
-
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.
-
High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high.
Octane myths
High octane gasoline improves mileage.
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that a tune-up will give you the same improvement on 87 octane gasoline.
High octane gasoline increases power.
If your car is designed to run on 87 octane gasoline, you shouldn't notice any more power on high octane gasoline. Again, if it does make a noticeable difference, you may need a tune-up.
AL&hpage=true&agency=Commerce
The higher the octane, the slower the speed of the burn; the lower the octane the faster the burn. If the burn is too fast, uncontrolled combustion can occur. This most often is heard as “pinging†and is commonly referred to as detonation. This is because instead of burning through top dead center of the combustion stroke, the entire charge is ignited too early and explodes in the chamber and acts as a bomb. Conversely, if the speed of the burn is too slow, it continues after the useful work can be done in the motor and manifests itself as poor throttle response, reduced power output and increased emissions and fuel consumption.
An engineering fact: THE MOST HORSEPOWER IS MADE AT THE THRESHOLD OF DETONATION. We have often gained horsepower on the dyno and felt improved starting and driveability going from Premium grade gas to Regular. This change was recently quantified in a customer’s Ducati M900 by reducing the cranking time to start-up from 15 to 3 revolutions, although part of the improvement is explained below.
The multi-valve combustion chambers and their reduced flame front propagation distances in the modern engines virtually eliminates the need for high-octane gasoline.
Using high-octane gas in a car designed for regular accomplishes little except more rapid combustion of your money. Some refuse to believe this, claiming, for example, that premium gives the family Toyota better mileage or more power. These people are in dreamland. Others say premium is purer or contains detergents that will cleanse your engine of uncouth deposits. Likewise misguided thinking--government regulations require detergents in all grades of gasoline. (BP Amoco, I notice, asserts that its premium gasoline contains more detergents than legally required; if you think that's worth 20 extra cents a gallon, be my guest.)
Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.
Here it is. Keep in mind, I'm just an automotive engineer, so I may not know much about how gasoline octane deviations might change the characteristics of combustion (or precombustion) inside a cylinder.
First, a couple definitions to get out of the way, since this often causes some confusion for folks:
RON: Research Octane Number
MON: Motor Octane Number
What goes into your tank, if you read whats on the label at the pump, is actually neither of these. Fuel from pumps (at least in the US) uses the (R+M)/2 formula, which means that they take an average of the two. Typically, your RON is about 8-10 points higher than your MON is. What this means is that fuel with a RON of 91 is actually going to be equivalent to somewhere between 86 and 87 {(R+M)/2, with R being 8-10 pts higher than M, is going to give a yield between 4 and 5 points down from R} I would guess that the RON posted on the body is for people in Europe and Austrailia, since that's where RON is the "headline" number listed on fuel there.
Octane itself is simply a rating of a fuel's resistance to autoignition. if you want a further explanation of it, read on:
Octane is measured as a relative mixture of isooctane (which is 2,2,4 trimethylpentane, an isomer of octane) and n-heptane. a fuel rated at 93 octane, for example, has a 93% mixture of isooctane to 7% n-heptane. The proportions of that mixture may not be precise, but the resistance to autoignition will be the same as if those were the exact proportions.
I can't give a definitive answer of what runs better, and nobody else can either. At least not for everyone. Ideal octane for a motor is going to vary based on atmospheric pressure, temperature, relative humidity, compression ratio, timing, and numerous other things. The best thing to do is to try each for yourself, check your mileage, and listen to what your butt is telling you. As for fuel mileage, additives are going to play a FAR greater role in fuel mileage than will the octane rating.
Octane, by definition, is the resistance to burn or detonation. The higher the rating, the slower the burn when ignited during the compression burn cycle of the piston.
-
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.
-
High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high.
Octane myths
High octane gasoline improves mileage.
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that a tune-up will give you the same improvement on 87 octane gasoline.
High octane gasoline increases power.
If your car is designed to run on 87 octane gasoline, you shouldn't notice any more power on high octane gasoline. Again, if it does make a noticeable difference, you may need a tune-up.
AL&hpage=true&agency=Commerce
The higher the octane, the slower the speed of the burn; the lower the octane the faster the burn. If the burn is too fast, uncontrolled combustion can occur. This most often is heard as “pinging†and is commonly referred to as detonation. This is because instead of burning through top dead center of the combustion stroke, the entire charge is ignited too early and explodes in the chamber and acts as a bomb. Conversely, if the speed of the burn is too slow, it continues after the useful work can be done in the motor and manifests itself as poor throttle response, reduced power output and increased emissions and fuel consumption.
An engineering fact: THE MOST HORSEPOWER IS MADE AT THE THRESHOLD OF DETONATION. We have often gained horsepower on the dyno and felt improved starting and driveability going from Premium grade gas to Regular. This change was recently quantified in a customer’s Ducati M900 by reducing the cranking time to start-up from 15 to 3 revolutions, although part of the improvement is explained below.
The multi-valve combustion chambers and their reduced flame front propagation distances in the modern engines virtually eliminates the need for high-octane gasoline.
Using high-octane gas in a car designed for regular accomplishes little except more rapid combustion of your money. Some refuse to believe this, claiming, for example, that premium gives the family Toyota better mileage or more power. These people are in dreamland. Others say premium is purer or contains detergents that will cleanse your engine of uncouth deposits. Likewise misguided thinking--government regulations require detergents in all grades of gasoline. (BP Amoco, I notice, asserts that its premium gasoline contains more detergents than legally required; if you think that's worth 20 extra cents a gallon, be my guest.)
Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.
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