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Octane Rating Is A Personal Choice
This is an article I wrote for the Thunderbird Club I am a member of.
In light of the recent increases in what everything costs some may decide to begin using or already have been using gasoline at a lower octane rating than what Ford recommends.
I suggest you read this article & then decide for yourself what is best for your type of driving and what you think is best for your 2002-2005 Thunderbird.
Octane Rating Is A Personal Choice
The 2002-05 Thunderbirds are recommended by Ford to use fuel rated at 91 octane, but what if the owner chooses not to. What could happen? Does myth, marketing or outdated information make your choices for you?
I began looking into this octane rating stuff. There are 3 very important terms that must be understood before considering what octane ratings to use. Compression Ratio. Octane Rating. Horsepower.
The Compression Stroke is one of the 4 strokes of all automotive gasoline engines in use today. This movement of the piston compresses the air & fuel mixture into a very small volume called the Compression Ratio. Gasoline-air vapor will self-combust or ignite when compressed. To help prevent this event from occurring, today’s gasoline has additives in the fuel to resist this phenomena. Dependent upon the amount of additive in the fuel, the more resistance the fuel-air mixture has to combustion under compression. This measure of resistance is known as 'octane' rating. The Compression Ratio of a vehicle’s engine determines the Octane Rating to use.
Octane is a hydrocarbon that, when burned in an engine, has a very high resistance to engine knock, or pinging. A common misconception is that gasoline with an octane rating of 87 contains 87% octane. The octane grade is not a measurement of how much octane is in the fuel but rather a measurement of how the fuel performs as compared to pure mixtures. Gasoline with an octane rating of 87 exhibits the same compression and detonation characteristics as a mixture of 87% octane and 13% heptane.
But Octane is very expensive, you never actually burn octane in your engine. The gasolines we use contain no octane. The octane rating simply measures how closely a gasoline compares to pure octane in suppressing knock. A fuel rated 93 octane will resist knock and pinging like a mixture that's 93 percent pure octane.
There are two different methods used to determine the octane rating of a fuel. There's "R," which stands for "research." The research octane number (RON) is determined in a lab with a test engine running at 600 rpm, which represents a low-compression, low-knock situation and comparing the results with pure octane/heptane mixtures.
The "M," is for "motor." The motor octane number (MON) uses a test engine, also in a lab, at a higher rpm running a preheated fuel mixture under load in a variable compression engine at higher RPMs than used in the RON method. The MON method is regarded as being a more accurate measurement and will return lower octane ratings then the RON method where knock is more likely.
The rating you see on pumps in the U.S. and Canada is an average of these two methods and is represented by the formula (R + M) / 2; and the quotient is the number posted on the pump. It is also commonly referred to as the “Anti-Knock Index” (AKI). This means if the RON of a fuel is 93 and the MON is 87, the octane rating you see on the pump is 90.
All the octane rating tells you is how much knock protection you get. A higher-than-necessary octane rating doesn't keep your engine cleaner, make the car go any faster or make your engine last longer.
The Octane Rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than the spark from the spark plug, it causes knocking in the engine. Knocking is some-thing you do not want to have happening. Engine damage can occur. Lower octane gas like "regular" 87-octane gasoline can handle the least amount of compression before igniting.
ALL gasoline sold in the United States & Canada have fuel additives which clean the combustion chamber. There is no increase or decrease in the amount of (nitrogen-based) cleaning additive in any given gallon or liter of gasoline. These additives are required by law. Different fuel retailers will label their fuel additives by differing marketing terms, it's all the same in terms of cleaning performance. Adding a bottle of fuel injection cleaner, etc. to a tank of modern gasoline is wasted money. These additives do not change the octane rating.
Horsepower. People talk about horsepower when they talk about high-performance cars. A high-performance engine has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight.
The 3.9L engine in the 2002-05 Thunderbird is a high-compression engine, with a compression ratio of 10.75:1. Regardless of what gasoline you put into the tank, the compression ratio is NOT going to change.
If you put 'regular' (87-octane) gasoline in your tank, and start your car, it will run and idle just fine. As you drive it down the road, it will run and perform just fine. As you accelerate hard for greater performance the ECM will advance the ignition timing to account for the milliseconds of expanding ignited fuel energy so that the engine can get the most efficient use of that energy to push the piston down. At the same time, the ECM is listening for spark-knock. If the ECM detects spark-knock, it will back-off of the ignition advance (slightly) until the spark-knock is no longer detected. This happens hundreds of times per second, and is indiscernible to the human ear or other senses. When the ignition timing advance is 'retarded', the engine is not operating at 'peak' performance, and therefore, you are not able to get the maximum engineered horsepower out of the engine at that moment. This is known as a performance 'degradation'.
Now, here is where all of this is important to the owner of a 2002-2005 Thunderbird. If you decide that you don't want to pay an additional ~50˘/gallon or liter at the pump and opt to fill the tank with 'regular' (87-octane) fuel, you're going to save about $9.00 per fill-up. If you drive your Thunderbird as a cruiser, you're going to realize little to no difference in the performance of your car. You will not gain or lose any MPG/MPL because there is no difference in energy content of premium fuel versus regular fuel. Now, if you drive your car like you stole it, accelerate hard from a stop, and put your foot into it when you are accelerating on the highway, you may be able to notice, or I should more accurately say "measure", a minor horsepower reduction as opposed to the same driving-style with a tank of 91-octane. Why? - Because the ECM is detecting spark-knock and retarding the ignition advance to eliminate it, which takes away from the maximum-engineered engine performance potential. So, if you don't drive your Thunderbird hard, you may/can opt for 87-octane fuel.
Ford has included this information in your operator's manual:
"Your vehicle is designed to use 91 “Premium” unleaded gasoline with an (R+M)/2 octane rating of 91 or higher for optimum performance. The use of gasolines with lower octane ratings may degrade performance. We do not recommend the use
of gasolines labeled as “Premium” in high altitude areas that are sold with octane ratings of less than 91. Do not be concerned if your engine sometimes knocks lightly. However, if it knocks heavily under most driving conditions while you are using fuel with the recommended octane rating, see your dealer or a qualified service technician to prevent any engine damage."
Two keywords are in this statement from Ford, "optimum" and "may". The choice of octane levels is yours to make accordingly to your driving habits plus what you now know about gasoline.
“A Smile in Every Mile”
Mike Schwartz
Steelblue5505
This is an article I wrote for the Thunderbird Club I am a member of.
In light of the recent increases in what everything costs some may decide to begin using or already have been using gasoline at a lower octane rating than what Ford recommends.
I suggest you read this article & then decide for yourself what is best for your type of driving and what you think is best for your 2002-2005 Thunderbird.
Octane Rating Is A Personal Choice
The 2002-05 Thunderbirds are recommended by Ford to use fuel rated at 91 octane, but what if the owner chooses not to. What could happen? Does myth, marketing or outdated information make your choices for you?
I began looking into this octane rating stuff. There are 3 very important terms that must be understood before considering what octane ratings to use. Compression Ratio. Octane Rating. Horsepower.
The Compression Stroke is one of the 4 strokes of all automotive gasoline engines in use today. This movement of the piston compresses the air & fuel mixture into a very small volume called the Compression Ratio. Gasoline-air vapor will self-combust or ignite when compressed. To help prevent this event from occurring, today’s gasoline has additives in the fuel to resist this phenomena. Dependent upon the amount of additive in the fuel, the more resistance the fuel-air mixture has to combustion under compression. This measure of resistance is known as 'octane' rating. The Compression Ratio of a vehicle’s engine determines the Octane Rating to use.
Octane is a hydrocarbon that, when burned in an engine, has a very high resistance to engine knock, or pinging. A common misconception is that gasoline with an octane rating of 87 contains 87% octane. The octane grade is not a measurement of how much octane is in the fuel but rather a measurement of how the fuel performs as compared to pure mixtures. Gasoline with an octane rating of 87 exhibits the same compression and detonation characteristics as a mixture of 87% octane and 13% heptane.
But Octane is very expensive, you never actually burn octane in your engine. The gasolines we use contain no octane. The octane rating simply measures how closely a gasoline compares to pure octane in suppressing knock. A fuel rated 93 octane will resist knock and pinging like a mixture that's 93 percent pure octane.
There are two different methods used to determine the octane rating of a fuel. There's "R," which stands for "research." The research octane number (RON) is determined in a lab with a test engine running at 600 rpm, which represents a low-compression, low-knock situation and comparing the results with pure octane/heptane mixtures.
The "M," is for "motor." The motor octane number (MON) uses a test engine, also in a lab, at a higher rpm running a preheated fuel mixture under load in a variable compression engine at higher RPMs than used in the RON method. The MON method is regarded as being a more accurate measurement and will return lower octane ratings then the RON method where knock is more likely.
The rating you see on pumps in the U.S. and Canada is an average of these two methods and is represented by the formula (R + M) / 2; and the quotient is the number posted on the pump. It is also commonly referred to as the “Anti-Knock Index” (AKI). This means if the RON of a fuel is 93 and the MON is 87, the octane rating you see on the pump is 90.
All the octane rating tells you is how much knock protection you get. A higher-than-necessary octane rating doesn't keep your engine cleaner, make the car go any faster or make your engine last longer.
The Octane Rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than the spark from the spark plug, it causes knocking in the engine. Knocking is some-thing you do not want to have happening. Engine damage can occur. Lower octane gas like "regular" 87-octane gasoline can handle the least amount of compression before igniting.
ALL gasoline sold in the United States & Canada have fuel additives which clean the combustion chamber. There is no increase or decrease in the amount of (nitrogen-based) cleaning additive in any given gallon or liter of gasoline. These additives are required by law. Different fuel retailers will label their fuel additives by differing marketing terms, it's all the same in terms of cleaning performance. Adding a bottle of fuel injection cleaner, etc. to a tank of modern gasoline is wasted money. These additives do not change the octane rating.
Horsepower. People talk about horsepower when they talk about high-performance cars. A high-performance engine has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight.
The 3.9L engine in the 2002-05 Thunderbird is a high-compression engine, with a compression ratio of 10.75:1. Regardless of what gasoline you put into the tank, the compression ratio is NOT going to change.
If you put 'regular' (87-octane) gasoline in your tank, and start your car, it will run and idle just fine. As you drive it down the road, it will run and perform just fine. As you accelerate hard for greater performance the ECM will advance the ignition timing to account for the milliseconds of expanding ignited fuel energy so that the engine can get the most efficient use of that energy to push the piston down. At the same time, the ECM is listening for spark-knock. If the ECM detects spark-knock, it will back-off of the ignition advance (slightly) until the spark-knock is no longer detected. This happens hundreds of times per second, and is indiscernible to the human ear or other senses. When the ignition timing advance is 'retarded', the engine is not operating at 'peak' performance, and therefore, you are not able to get the maximum engineered horsepower out of the engine at that moment. This is known as a performance 'degradation'.
Now, here is where all of this is important to the owner of a 2002-2005 Thunderbird. If you decide that you don't want to pay an additional ~50˘/gallon or liter at the pump and opt to fill the tank with 'regular' (87-octane) fuel, you're going to save about $9.00 per fill-up. If you drive your Thunderbird as a cruiser, you're going to realize little to no difference in the performance of your car. You will not gain or lose any MPG/MPL because there is no difference in energy content of premium fuel versus regular fuel. Now, if you drive your car like you stole it, accelerate hard from a stop, and put your foot into it when you are accelerating on the highway, you may be able to notice, or I should more accurately say "measure", a minor horsepower reduction as opposed to the same driving-style with a tank of 91-octane. Why? - Because the ECM is detecting spark-knock and retarding the ignition advance to eliminate it, which takes away from the maximum-engineered engine performance potential. So, if you don't drive your Thunderbird hard, you may/can opt for 87-octane fuel.
Ford has included this information in your operator's manual:
"Your vehicle is designed to use 91 “Premium” unleaded gasoline with an (R+M)/2 octane rating of 91 or higher for optimum performance. The use of gasolines with lower octane ratings may degrade performance. We do not recommend the use
of gasolines labeled as “Premium” in high altitude areas that are sold with octane ratings of less than 91. Do not be concerned if your engine sometimes knocks lightly. However, if it knocks heavily under most driving conditions while you are using fuel with the recommended octane rating, see your dealer or a qualified service technician to prevent any engine damage."
Two keywords are in this statement from Ford, "optimum" and "may". The choice of octane levels is yours to make accordingly to your driving habits plus what you now know about gasoline.
“A Smile in Every Mile”
Mike Schwartz
Steelblue5505
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