Fuel Octane: Performance and Milage
07-02-2003, 05:13 AM
#1
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Fuel Octane: Performance and Milage
The owners manual says that the '04 Max can burn 87 octane and up. It does warn that performance will be degraded by the lower octane fuels, which makes perfect sense. I've experimented with 89 and 87 octane gas and can tell some difference in performance, but for the vast majority, it's only affected when hammering on it. Mostly, it runs fine on anything.
I do wonder though, if you get less gas milage with low octane gas. If the knock sensors retard the timing, does that cause you to burn more fuel? Has anyone else experimented with lower octanes? Any engineers or motorheads on the board?
I do wonder though, if you get less gas milage with low octane gas. If the knock sensors retard the timing, does that cause you to burn more fuel? Has anyone else experimented with lower octanes? Any engineers or motorheads on the board?
07-02-2003, 06:18 AM
#2
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Re: Fuel Octane: Performance and Milage
Originally posted by jacksprat01
The owners manual says that the '04 Max can burn 87 octane and up. It does warn that performance will be degraded by the lower octane fuels, which makes perfect sense. I've experimented with 89 and 87 octane gas and can tell some difference in performance, but for the vast majority, it's only affected when hammering on it. Mostly, it runs fine on anything.
I do wonder though, if you get less gas milage with low octane gas. If the knock sensors retard the timing, does that cause you to burn more fuel? Has anyone else experimented with lower octanes? Any engineers or motorheads on the board?
The owners manual says that the '04 Max can burn 87 octane and up. It does warn that performance will be degraded by the lower octane fuels, which makes perfect sense. I've experimented with 89 and 87 octane gas and can tell some difference in performance, but for the vast majority, it's only affected when hammering on it. Mostly, it runs fine on anything.
I do wonder though, if you get less gas milage with low octane gas. If the knock sensors retard the timing, does that cause you to burn more fuel? Has anyone else experimented with lower octanes? Any engineers or motorheads on the board?
07-02-2003, 06:39 AM
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Re: Re: Fuel Octane: Performance and Milage
Originally posted by JAKE02
I'm not a motor-head, however I think common sense will tell you with a high-performance engine like the VQ anything less than premium fuel will decrease performance and gas mileage.
I'm not a motor-head, however I think common sense will tell you with a high-performance engine like the VQ anything less than premium fuel will decrease performance and gas mileage.
07-02-2003, 07:32 AM
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Re: Re: Re: Fuel Octane: Performance and Milage
Originally posted by jacksprat01
As I said, I'm already sure that the performance is decreased. I just not sure about the milage. There is likely a reduction in milage with lower octane, but by how much? Is it a tenth of one mile per gallon? If so, it might not justify the additional expense of super.
As I said, I'm already sure that the performance is decreased. I just not sure about the milage. There is likely a reduction in milage with lower octane, but by how much? Is it a tenth of one mile per gallon? If so, it might not justify the additional expense of super.
07-02-2003, 09:29 AM
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Re: Fuel Octane: Performance and Milage
Originally posted by jacksprat01
I've experimented with 89 and 87 octane gas and can tell some difference in performance, but for the vast majority, it's only affected when hammering on it.
I've experimented with 89 and 87 octane gas and can tell some difference in performance, but for the vast majority, it's only affected when hammering on it.
You may notice a difference in fuel economy, and if you tested it properly, maybe you would notice a difference in the 1/4 mile time or some other measured distance. But there is no way you are noticing a difference between the two when driving around town... that is just not possible.
07-02-2003, 09:42 AM
#7
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Re: Re: Fuel Octane: Performance and Milage
Um, I think you are agreeing with me. As I said, I only notice the advantage of super when hammering on it.
Originally posted by gmc74
Come on, you must be kidding!
You may notice a difference in fuel economy, and if you tested it properly, maybe you would notice a difference in the 1/4 mile time or some other measured distance. But there is no way you are noticing a difference between the two when driving around town... that is just not possible.
Come on, you must be kidding!
You may notice a difference in fuel economy, and if you tested it properly, maybe you would notice a difference in the 1/4 mile time or some other measured distance. But there is no way you are noticing a difference between the two when driving around town... that is just not possible.
07-02-2003, 11:14 AM
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Re: Re: Fuel Octane: Performance and Milage
Originally posted by gmc74
Come on, you must be kidding!
You may notice a difference in fuel economy, and if you tested it properly, maybe you would notice a difference in the 1/4 mile time or some other measured distance. But there is no way you are noticing a difference between the two when driving around town... that is just not possible.
Come on, you must be kidding!
You may notice a difference in fuel economy, and if you tested it properly, maybe you would notice a difference in the 1/4 mile time or some other measured distance. But there is no way you are noticing a difference between the two when driving around town... that is just not possible.
07-02-2003, 11:31 AM
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I don't think that is physically possible, the difference is going to be so small. Hammering it, driving around town, etc...
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
07-02-2003, 12:25 PM
#10
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Originally posted by gmc74
I don't think that is physically possible, the difference is going to be so small. Hammering it, driving around town, etc...
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
I don't think that is physically possible, the difference is going to be so small. Hammering it, driving around town, etc...
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
I don't have hard statistics to prove it, but if you are in tune with your car, you should be able to feel the improved response and acceleration with Super.But dammit, we digress! I want hard facts about fuel economy! Anyone?
07-02-2003, 01:02 PM
#11
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Originally posted by gmc74
I don't think that is physically possible, the difference is going to be so small. Hammering it, driving around town, etc...
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
I don't think that is physically possible, the difference is going to be so small. Hammering it, driving around town, etc...
I would love to hear how you both experimented with this process that leads you to think that there is some noticable difference.
Ok, lets go over this one more time, I will try and type slowly.........We put 87/89 octane gas in tank and take off full throttle a lot during that tank.....we notice "by the seat of your pants" the "feeling" your car has, i.e. power. Then we put 93 octane gas in (after tank is nearly empty of 87/89 octane) and we take off a lot full throttle during that tank and we feel as though the car has more power.......god man this has been discussed in the 5th gen forums forever, with many org members relating this. jacksprat01 is right man get in tune with your car....sorry this is not scientific enough for you, realizing your **** retentive tendancies, I will try and cut some slack...
07-02-2003, 01:23 PM
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Originally posted by JAKE02
Ok, lets go over this one more time, I will try and type slowly.........We put 87/89 octane gas in tank and take off full throttle a lot during that tank.....we notice "by the seat of your pants" the "feeling" your car has, i.e. power. Then we put 93 octane gas in (after tank is nearly empty of 87/89 octane) and we take off a lot full throttle during that tank and we feel as though the car has more power.......god man this has been discussed in the 5th gen forums forever, with many org members relating this. jacksprat01 is right man get in tune with your car....sorry this is not scientific enough for you, realizing your **** retentive tendancies, I will try and cut some slack...
Ok, lets go over this one more time, I will try and type slowly.........We put 87/89 octane gas in tank and take off full throttle a lot during that tank.....we notice "by the seat of your pants" the "feeling" your car has, i.e. power. Then we put 93 octane gas in (after tank is nearly empty of 87/89 octane) and we take off a lot full throttle during that tank and we feel as though the car has more power.......god man this has been discussed in the 5th gen forums forever, with many org members relating this. jacksprat01 is right man get in tune with your car....sorry this is not scientific enough for you, realizing your **** retentive tendancies, I will try and cut some slack...
I think I will give it a shot and see what happens. I think you would need to run a few tanks of super after regular and vice versa before you can accurately calculate it.
07-02-2003, 02:03 PM
#13
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i'm no engineer either - i understood that a higher octane just kept the engine from knocking.
here's what i have ...
Fuel octane requirements for gasoline engines vary with the compression ratio of the engine; diesel cetane requirements also vary with the compression ratio. Engine compression ratio is the relative volume of a cylinder from the bottom most position of the piston's stroke to the top most position of the piston's stroke. The higher an engine's compression ratio, the greater the amount of heat generated in the cylinder during the compression stroke.
Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns. Higher octane fuel contains more POTENTIAL energy but requires the higher heat generated by higher compression ratio engines to properly condition the fuel to RELEASE that higher potential energy. In the refining process, fewer gallons of higher octane fuels are yielded from a barrel of raw crude.
If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power and possible engine damage. The operator hears an audible "knock" or "ping", referred to as detonation. Detonation may vary from a faint noise on light acceleration to a constant, deep hammering noise while driving at a constant speed. Improper timing adjustments, vacuum leaks, or excessively lean fuel mixtures may also cause detonation.
Many vehicle owners believe that higher octane fuels are better for their vehicles since they are labeled "PREMIUM." The logic is that since it is a premium fuel it must be better. In reality, the premium label originates from the higher cost to refine and the resultant higher retail cost. Some refiners label their high octane fuels "SUPER." Some owners think that these fuels will make their vehicles more powerful. Only engines with high compression ratios can deliver all the potential energy from higher octane fuels! Always consult the manufacturer's octane recommendation to determine the proper octane requirements for any given vehicle. Generally, engines with compression ratios of 9.3 : 1 or less will safely operate with unleaded 87 octane fuel. Engines with higher compression ratios usually require higher octane fuels.
Many owners who operate vehicles designed to operate on 87 octane fuel experience ping and knock. They usually "fix" this problem by purchasing the higher priced, higher octane fuels. Most owner's manuals indicate that some light and intermittent ping is normal but that heavy or sustained ping or knock should be attended to by either purchasing the correct octane fuel or servicing the engine.
Most fuel refiners blend fuels for geographic areas and adjust their blends seasonally. These blending techniques compensate for the decrease in oxygen content with an increase in altitude and compensate for volatility during the warmer or cooler seasons. Significant ambient temperature changes (40 degrees Fahrenheit) or altitude changes (4,000 feet) may cause some serious engine detonation. This problem is usually corrected by filling the tank with "local" fuel that has been properly blended for season and altitude.
here's what i have ...
Fuel octane requirements for gasoline engines vary with the compression ratio of the engine; diesel cetane requirements also vary with the compression ratio. Engine compression ratio is the relative volume of a cylinder from the bottom most position of the piston's stroke to the top most position of the piston's stroke. The higher an engine's compression ratio, the greater the amount of heat generated in the cylinder during the compression stroke.
Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns. Higher octane fuel contains more POTENTIAL energy but requires the higher heat generated by higher compression ratio engines to properly condition the fuel to RELEASE that higher potential energy. In the refining process, fewer gallons of higher octane fuels are yielded from a barrel of raw crude.
If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power and possible engine damage. The operator hears an audible "knock" or "ping", referred to as detonation. Detonation may vary from a faint noise on light acceleration to a constant, deep hammering noise while driving at a constant speed. Improper timing adjustments, vacuum leaks, or excessively lean fuel mixtures may also cause detonation.
Many vehicle owners believe that higher octane fuels are better for their vehicles since they are labeled "PREMIUM." The logic is that since it is a premium fuel it must be better. In reality, the premium label originates from the higher cost to refine and the resultant higher retail cost. Some refiners label their high octane fuels "SUPER." Some owners think that these fuels will make their vehicles more powerful. Only engines with high compression ratios can deliver all the potential energy from higher octane fuels! Always consult the manufacturer's octane recommendation to determine the proper octane requirements for any given vehicle. Generally, engines with compression ratios of 9.3 : 1 or less will safely operate with unleaded 87 octane fuel. Engines with higher compression ratios usually require higher octane fuels.
Many owners who operate vehicles designed to operate on 87 octane fuel experience ping and knock. They usually "fix" this problem by purchasing the higher priced, higher octane fuels. Most owner's manuals indicate that some light and intermittent ping is normal but that heavy or sustained ping or knock should be attended to by either purchasing the correct octane fuel or servicing the engine.
Most fuel refiners blend fuels for geographic areas and adjust their blends seasonally. These blending techniques compensate for the decrease in oxygen content with an increase in altitude and compensate for volatility during the warmer or cooler seasons. Significant ambient temperature changes (40 degrees Fahrenheit) or altitude changes (4,000 feet) may cause some serious engine detonation. This problem is usually corrected by filling the tank with "local" fuel that has been properly blended for season and altitude.
07-02-2003, 02:06 PM
#14
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Originally posted by gmc74
First, I thought he was comparing 87 to 89 based on his first post. I take it from your last post you are comparing them to super. I still have a hard time beleiving that you are really feeling the difference it sounds more like you are feeling the difference that your brain says must be there because you just dropped an extra 10-20% per gallon on your gas. That being said, I have never tested it so I can't say for sure. I do beleive that you may notice better gas mileage. I doubt the gas mileage and/or performance boost is in the 10-20% range.
I think I will give it a shot and see what happens. I think you would need to run a few tanks of super after regular and vice versa before you can accurately calculate it.
First, I thought he was comparing 87 to 89 based on his first post. I take it from your last post you are comparing them to super. I still have a hard time beleiving that you are really feeling the difference it sounds more like you are feeling the difference that your brain says must be there because you just dropped an extra 10-20% per gallon on your gas. That being said, I have never tested it so I can't say for sure. I do beleive that you may notice better gas mileage. I doubt the gas mileage and/or performance boost is in the 10-20% range.
I think I will give it a shot and see what happens. I think you would need to run a few tanks of super after regular and vice versa before you can accurately calculate it.
07-02-2003, 02:30 PM
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ok Mr generalities... you must be a democrat, you can't prove anything, you don't put any effort in to proving anything, fact or fiction if you feel it then it must be... screw proving something right or wrong, lets just all feel that it must be right and then it shall be...
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
07-02-2003, 02:43 PM
#16
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Originally posted by gmc74
ok Mr generalities... you must be a democrat, you can't prove anything, you don't put any effort in to proving anything, fact or fiction if you feel it then it must be... screw proving something right or wrong, lets just all feel that it must be right and then it shall be...
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
ok Mr generalities... you must be a democrat, you can't prove anything, you don't put any effort in to proving anything, fact or fiction if you feel it then it must be... screw proving something right or wrong, lets just all feel that it must be right and then it shall be...
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
feel better now...... you put way too much into an internet forum.........keep it....you are slowly but surely becoming a joke here. I dont accept bullsh!t (sound famaliar) from idiots like yourself....people who are constantly talking out of both sides of their big trap...this is a good one...quote gmc" you have to through out personal insults to prove your point" end quote when my god man you are the mastering at slinging **** around here.....your wife must keep you on a short leash at home....that is why you feel the need to "act" like you are the supreme being here.....what a joke.
07-02-2003, 03:59 PM
#17
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Originally posted by JAKE02
feel better now...... you put way too much into an internet forum.........keep it....you are slowly but surely becoming a joke here. I dont accept bullsh!t (sound famaliar) from idiots like yourself....people who are constantly talking out of both sides of their big trap...this is a good one...quote gmc" you have to through out personal insults to prove your point" end quote when my god man you are the mastering at slinging **** around here.....your wife must keep you on a short leash at home....that is why you feel the need to "act" like you are the supreme being here.....what a joke.
feel better now...... you put way too much into an internet forum.........keep it....you are slowly but surely becoming a joke here. I dont accept bullsh!t (sound famaliar) from idiots like yourself....people who are constantly talking out of both sides of their big trap...this is a good one...quote gmc" you have to through out personal insults to prove your point" end quote when my god man you are the mastering at slinging **** around here.....your wife must keep you on a short leash at home....that is why you feel the need to "act" like you are the supreme being here.....what a joke.
If I am slowly but surely becoming you, then I would go away... I am not the one that hangs out in a different forum just to insult the people that buy that car...
What did I post that was a personal insult? That you are probably a democrat? That people like you annoy the **** out of me? Those aren't personal insults. You are an a$$ would be a personal insult.
07-02-2003, 05:15 PM
#18
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Originally posted by gmc74
Yeah, you post crap and then think no one will question what you state as fact... but then someone does... and your witty response? BLAH...
If I am slowly but surely becoming you, then I would go away... I am not the one that hangs out in a different forum just to insult the people that buy that car...
What did I post that was a personal insult? That you are probably a democrat? That people like you annoy the **** out of me? Those aren't personal insults. You are an a$$ would be a personal insult.
Yeah, you post crap and then think no one will question what you state as fact... but then someone does... and your witty response? BLAH...
If I am slowly but surely becoming you, then I would go away... I am not the one that hangs out in a different forum just to insult the people that buy that car...
What did I post that was a personal insult? That you are probably a democrat? That people like you annoy the **** out of me? Those aren't personal insults. You are an a$$ would be a personal insult.
07-02-2003, 05:46 PM
#19
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BTW, back on topic... I was reading about how your car is affected by the different octane rated gasolines and for the most part, everything that I have read states that all it does it keep your engine from knocking. If your engine isn't knocking or pinging then it is combusting properly. If it is combusting properly then you will get the maximum performance and fuel efficiency.
If it is knocking then you need to raise the octane level, thus raising the temperature that the fuel combusts at, which in turn causes the knocking (which is just some of the fuel combusting before it is intended to) to go away.
How do manufacturers come up with the rating? Well one report that I read stated that they actually use a single cylinder mock engine in order to test the combustion rate. The study stated that this is why a lot of times a higher octane is recommended but not necessarily needed.
I found all of that from googling- octane, gas, performance, and mileage in different combinations.
I am still going to give it a shot. I will run it low tomorrow and fill it with Super. Then watch my mileage and see if I notice a difference in performance. Then compare that to Regular gas and see what the difference is. I was thinking that I may get a slight mileage increase, but based on what I read I am not sure that I will... we will see.
If it is knocking then you need to raise the octane level, thus raising the temperature that the fuel combusts at, which in turn causes the knocking (which is just some of the fuel combusting before it is intended to) to go away.
How do manufacturers come up with the rating? Well one report that I read stated that they actually use a single cylinder mock engine in order to test the combustion rate. The study stated that this is why a lot of times a higher octane is recommended but not necessarily needed.
I found all of that from googling- octane, gas, performance, and mileage in different combinations.
I am still going to give it a shot. I will run it low tomorrow and fill it with Super. Then watch my mileage and see if I notice a difference in performance. Then compare that to Regular gas and see what the difference is. I was thinking that I may get a slight mileage increase, but based on what I read I am not sure that I will... we will see.
07-02-2003, 06:30 PM
#20
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Join Date: Jun 2003
Posts: 18
Here is what I will do.
I am starting a trip from Atlanta, GA to Port St. Lucie tomorrow in my spanking new Maxima and I will fill it up with regular for the trip down and high octance on the way back and report the mileage for each segment.
I will be back on Monday, but will report the trip down mileage tomorrow.
I am starting a trip from Atlanta, GA to Port St. Lucie tomorrow in my spanking new Maxima and I will fill it up with regular for the trip down and high octance on the way back and report the mileage for each segment.
I will be back on Monday, but will report the trip down mileage tomorrow.
07-02-2003, 06:36 PM
#21
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Join Date: Apr 2003
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Originally posted by gmc74
ok Mr generalities... you must be a democrat, you can't prove anything, you don't put any effort in to proving anything, fact or fiction if you feel it then it must be... screw proving something right or wrong, lets just all feel that it must be right and then it shall be...
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
ok Mr generalities... you must be a democrat, you can't prove anything, you don't put any effort in to proving anything, fact or fiction if you feel it then it must be... screw proving something right or wrong, lets just all feel that it must be right and then it shall be...
damn, people like you annoy the **** out of me. I am not really sure why, every society needs bottom feeders, and people who accept what they are spoon fed with out questioning why. You fill that void.
07-02-2003, 06:51 PM
#22
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Join Date: Apr 2003
Location: Las Vegas, NV
Posts: 95
If you drive 15,000 miles a year and average 25 MPG (insert your own numbers here), you will use 600 gallons of gas per year. If 89 octane gas is 10 cents cheaper than 91 octane and 87 octane is 20 cents cheaper than 91 octane, you will save $60/year if you switch from 91 octane to 89 octane and $120/year if you switch from 91 octane to 87 octane.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
07-02-2003, 06:58 PM
#23
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Originally posted by gmc74
BTW, back on topic... I was reading about how your car is affected by the different octane rated gasolines and for the most part, everything that I have read states that all it does it keep your engine from knocking. If your engine isn't knocking or pinging then it is combusting properly. If it is combusting properly then you will get the maximum performance and fuel efficiency.
If it is knocking then you need to raise the octane level, thus raising the temperature that the fuel combusts at, which in turn causes the knocking (which is just some of the fuel combusting before it is intended to) to go away.
How do manufacturers come up with the rating? Well one report that I read stated that they actually use a single cylinder mock engine in order to test the combustion rate. The study stated that this is why a lot of times a higher octane is recommended but not necessarily needed.
I found all of that from googling- octane, gas, performance, and mileage in different combinations.
I am still going to give it a shot. I will run it low tomorrow and fill it with Super. Then watch my mileage and see if I notice a difference in performance. Then compare that to Regular gas and see what the difference is. I was thinking that I may get a slight mileage increase, but based on what I read I am not sure that I will... we will see.
BTW, back on topic... I was reading about how your car is affected by the different octane rated gasolines and for the most part, everything that I have read states that all it does it keep your engine from knocking. If your engine isn't knocking or pinging then it is combusting properly. If it is combusting properly then you will get the maximum performance and fuel efficiency.
If it is knocking then you need to raise the octane level, thus raising the temperature that the fuel combusts at, which in turn causes the knocking (which is just some of the fuel combusting before it is intended to) to go away.
How do manufacturers come up with the rating? Well one report that I read stated that they actually use a single cylinder mock engine in order to test the combustion rate. The study stated that this is why a lot of times a higher octane is recommended but not necessarily needed.
I found all of that from googling- octane, gas, performance, and mileage in different combinations.
I am still going to give it a shot. I will run it low tomorrow and fill it with Super. Then watch my mileage and see if I notice a difference in performance. Then compare that to Regular gas and see what the difference is. I was thinking that I may get a slight mileage increase, but based on what I read I am not sure that I will... we will see.
07-02-2003, 07:08 PM
#24
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Join Date: Jun 2003
Posts: 18
Originally posted by alpine205
If you drive 15,000 miles a year and average 25 MPG (insert your own numbers here), you will use 600 gallons of gas per year. If 89 octane gas is 10 cents cheaper than 91 octane and 87 octane is 20 cents cheaper than 91 octane, you will save $60/year if you switch from 91 octane to 89 octane and $120/year if you switch from 91 octane to 87 octane.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
If you drive 15,000 miles a year and average 25 MPG (insert your own numbers here), you will use 600 gallons of gas per year. If 89 octane gas is 10 cents cheaper than 91 octane and 87 octane is 20 cents cheaper than 91 octane, you will save $60/year if you switch from 91 octane to 89 octane and $120/year if you switch from 91 octane to 87 octane.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
07-02-2003, 07:20 PM
#25
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Join Date: Jun 2003
Posts: 70
$120 a year is cheap if it is really reaping benefits for you. If it doesn't make a noticable difference, it's money wasted, regardless of how little. Besides, super uses more crude so we need to make more trips to the middle east.
Originally posted by alpine205
If you drive 15,000 miles a year and average 25 MPG (insert your own numbers here), you will use 600 gallons of gas per year. If 89 octane gas is 10 cents cheaper than 91 octane and 87 octane is 20 cents cheaper than 91 octane, you will save $60/year if you switch from 91 octane to 89 octane and $120/year if you switch from 91 octane to 87 octane.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
If you drive 15,000 miles a year and average 25 MPG (insert your own numbers here), you will use 600 gallons of gas per year. If 89 octane gas is 10 cents cheaper than 91 octane and 87 octane is 20 cents cheaper than 91 octane, you will save $60/year if you switch from 91 octane to 89 octane and $120/year if you switch from 91 octane to 87 octane.
Now, I paid $30,000+ for my Max so, you know what, call me a wild man but I'm just going to go for it and use 91 octane all the time. After all, I never know when one of them there supercharged Grand Prixs might pull up next to me at a red light.
Interesting discussion though -- in theory.
07-02-2003, 08:53 PM
#26
Senior Member
Join Date: Jun 2003
Location: Colorado Springs, Colorado
Posts: 1,994
Coffeeshark, you basically got it correct in your post. I will only comment where some of your points are off or need clarification. I worked for an oil company for 35 years and know a little about this subject. I will also comment in another post elswhere in this thread about my gasoline mileage experience with my new SilverMax.
[QUOTE]Originally posted by coffeeshark
[B]i'm no engineer either - i understood that a higher octane just kept the engine from knocking.
here's what i have ...
Fuel octane requirements for gasoline engines vary with the compression ratio of the engine; diesel cetane requirements also vary with the compression ratio.
~~~~~~~~~~
Comment: While an engine's compression ratio is important in determining its octane requirement, those requirements are also dependant on the engine technology designed into that gasoline engine. The 3.5L VQ engine in the Maxima is among the most advanced in engine technology today (see Wards Automotive 10 Best Engines for more details).
Octane is basically a measure of a gasoline's resistance to burning (prematurely). In diesel engines, cetane is a measure of a fuel's ability to burn. The higher the cetane the cleaner burning the fuel. Because in a diesel engine the fuel is injected into the cylinder at the proper instance for combustion, those engines' compression ratios have little effect on cetane requirements. (enough about diesels).
~~~~~~~~~~~~~~~~~~~~
Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns.
~~~~~~~~~~~~~~~~~~~
Comment: While you are correct about the slower burning property of premium gasoline, the volatility of premium gasoline (evaporative qualities) is not directly correlated with its octane. The volatility of each grade of gasoline is determined in the blending process (and is usually set as high as the regulations allow for that time of year).
~~~~~~~~~~~~~~~~~~~
Only engines with high compression ratios can deliver all the potential energy from higher octane fuels!
~~~~~~~~~~~~~~~~~~~
Comment: It also helps to have modern engine technology to capture a fuel's full potential.
~~~~~~~~~~~~~~~~~~~
Most fuel refiners blend fuels for geographic areas and adjust their blends seasonally.
~~~~~~~~~~~~~~~~~~
Comment: All refiners blend their gasolines according to EPA regulations for their marketing area and the season of the year.
~~~~~~~~~~~~~~~~~~
These blending techniques compensate for the decrease in oxygen content with an increase in altitude and compensate for volatility during the warmer or cooler seasons.
~~~~~~~~~~~~~~~~~~
Comment: It's not the decrease in oxygen content with altitude that's important, but the lower air pressure at higher altitudes. Because of the lower air pressure, it's possible to use a lower octane fuel without engine knock. Generally above 4,000 feet, 85 octane performs comparable to 87 octane at sea level. Thus, if you transported (via carrier) a vehicle with 85 octane in the tank from Denver to Los Angeles, you would likely have noticable knock (unless the engine technology compensated, which it might.)
Volatility is the ability of the fuel to vaporize. In the 1950s "vapor lock" was a common occurence because the fuel vaporized in the fuel line rather than in the carburator. With EPA mandated lower volatility gasolines in use today, you no longe see "vapor lock." What you do see is sometimes difficult starting situations in cold weather (particularly when a cold snap is premature).
[QUOTE]Originally posted by coffeeshark
[B]i'm no engineer either - i understood that a higher octane just kept the engine from knocking.
here's what i have ...
Fuel octane requirements for gasoline engines vary with the compression ratio of the engine; diesel cetane requirements also vary with the compression ratio.
~~~~~~~~~~
Comment: While an engine's compression ratio is important in determining its octane requirement, those requirements are also dependant on the engine technology designed into that gasoline engine. The 3.5L VQ engine in the Maxima is among the most advanced in engine technology today (see Wards Automotive 10 Best Engines for more details).
Octane is basically a measure of a gasoline's resistance to burning (prematurely). In diesel engines, cetane is a measure of a fuel's ability to burn. The higher the cetane the cleaner burning the fuel. Because in a diesel engine the fuel is injected into the cylinder at the proper instance for combustion, those engines' compression ratios have little effect on cetane requirements. (enough about diesels).
~~~~~~~~~~~~~~~~~~~~
Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns.
~~~~~~~~~~~~~~~~~~~
Comment: While you are correct about the slower burning property of premium gasoline, the volatility of premium gasoline (evaporative qualities) is not directly correlated with its octane. The volatility of each grade of gasoline is determined in the blending process (and is usually set as high as the regulations allow for that time of year).
~~~~~~~~~~~~~~~~~~~
Only engines with high compression ratios can deliver all the potential energy from higher octane fuels!
~~~~~~~~~~~~~~~~~~~
Comment: It also helps to have modern engine technology to capture a fuel's full potential.
~~~~~~~~~~~~~~~~~~~
Most fuel refiners blend fuels for geographic areas and adjust their blends seasonally.
~~~~~~~~~~~~~~~~~~
Comment: All refiners blend their gasolines according to EPA regulations for their marketing area and the season of the year.
~~~~~~~~~~~~~~~~~~
These blending techniques compensate for the decrease in oxygen content with an increase in altitude and compensate for volatility during the warmer or cooler seasons.
~~~~~~~~~~~~~~~~~~
Comment: It's not the decrease in oxygen content with altitude that's important, but the lower air pressure at higher altitudes. Because of the lower air pressure, it's possible to use a lower octane fuel without engine knock. Generally above 4,000 feet, 85 octane performs comparable to 87 octane at sea level. Thus, if you transported (via carrier) a vehicle with 85 octane in the tank from Denver to Los Angeles, you would likely have noticable knock (unless the engine technology compensated, which it might.)
Volatility is the ability of the fuel to vaporize. In the 1950s "vapor lock" was a common occurence because the fuel vaporized in the fuel line rather than in the carburator. With EPA mandated lower volatility gasolines in use today, you no longe see "vapor lock." What you do see is sometimes difficult starting situations in cold weather (particularly when a cold snap is premature).
07-02-2003, 09:08 PM
#27
Senior Member
Join Date: Dec 2001
Posts: 717
Originally posted by gmc74
Yeah, you post crap and then think no one will question what you state as fact... but then someone does... and your witty response? BLAH...
If I am slowly but surely becoming you, then I would go away... I am not the one that hangs out in a different forum just to insult the people that buy that car...
What did I post that was a personal insult? That you are probably a democrat? That people like you annoy the **** out of me? Those aren't personal insults. You are an a$$ would be a personal insult.
Yeah, you post crap and then think no one will question what you state as fact... but then someone does... and your witty response? BLAH...
If I am slowly but surely becoming you, then I would go away... I am not the one that hangs out in a different forum just to insult the people that buy that car...
What did I post that was a personal insult? That you are probably a democrat? That people like you annoy the **** out of me? Those aren't personal insults. You are an a$$ would be a personal insult.
07-02-2003, 09:25 PM
#28
Senior Member
Join Date: Apr 2003
Posts: 1,282
Originally posted by JAKE02
Come on you have been throwing insults my way since the first day you came to this forum.......nice selective memory. Comments like "who let this idiot in here" and such have been the norm with you......and the only person I insult is YOU because of your "I'm superior attitude" you always have to have the last word on any thread no matter how ridiculous you sound...and get over the fact I'm in "your forum" I have interest in the 6th gen because it is the newest maxima....some of us have been max enthusiasts for years......and have owned multiple gen of maximas.
Come on you have been throwing insults my way since the first day you came to this forum.......nice selective memory. Comments like "who let this idiot in here" and such have been the norm with you......and the only person I insult is YOU because of your "I'm superior attitude" you always have to have the last word on any thread no matter how ridiculous you sound...and get over the fact I'm in "your forum" I have interest in the 6th gen because it is the newest maxima....some of us have been max enthusiasts for years......and have owned multiple gen of maximas.
I am sure you have interest here, great you are a max enthusiast... do you have to be an a$$ about it?
I post where I want to post, first, last or in the middle. Hey man, this is me, if you don't like it then ignore me. I am the same here that I am in person, and I really don't give a **** if you like it or not. Be a **** to me and I will be relentless in my pursuit to be a **** back, 10 fold.
07-02-2003, 09:38 PM
#29
Senior Member
Join Date: Dec 2001
Posts: 717
Originally posted by gmc74
yeah, somehow I just picked you out of the crowd to start insulting with out any reason.. nice one, did you come up with that on your own?
I am sure you have interest here, great you are a max enthusiast... do you have to be an a$$ about it?
I post where I want to post, first, last or in the middle. Hey man, this is me, if you don't like it then ignore me. I am the same here that I am in person, and I really don't give a **** if you like it or not. Be a **** to me and I will be relentless in my pursuit to be a **** back, 10 fold.
yeah, somehow I just picked you out of the crowd to start insulting with out any reason.. nice one, did you come up with that on your own?
I am sure you have interest here, great you are a max enthusiast... do you have to be an a$$ about it?
I post where I want to post, first, last or in the middle. Hey man, this is me, if you don't like it then ignore me. I am the same here that I am in person, and I really don't give a **** if you like it or not. Be a **** to me and I will be relentless in my pursuit to be a **** back, 10 fold.
07-03-2003, 01:28 AM
#30
Senior Member
Join Date: Jun 2003
Location: Colorado Springs, Colorado
Posts: 1,994
Octane and Mileage -- The Numbers
Originally posted by BoomerangThree
I have had friends with other cars, Acura, state that they get around a 10% improvement in mileage with Premium fuel. Can anyone validate this with facts and numbers?
I have had friends with other cars, Acura, state that they get around a 10% improvement in mileage with Premium fuel. Can anyone validate this with facts and numbers?
Some posters have asked for more science and less opinion. I'll give you mostly science (facts and numbers) with some opinion thrown in. But, before I give you the mileage numbers for my new SilverMaxima, I'd like to quote the owners' manual on octane:
"Use unleaded gasoline with an octane rating of at least 87 AKI (Anti-Knock Index). For improved performance . . . use unleaded premium gasoline with an octane rating of at least 91." This means regular gasoline will work fine and that premium will work somewhat better where improved performance is needed. There are really only two places where premium is "needed" -- if you experience severe engine knock, or if you're racing or otherwise calling for maximum acceleration frequently. Otherwise, save the 20 cents/gallon and buy regular.
I live in Colorado and normally drive at elevations between 6,000 feet and 7,200 feet above sea level. For this situation, the manual has the following information on gasoline octane:
"However, you may use unleaded gasoline with an octane rating as low as 85 AKI in high altitude areas [over 4,000 ft] such as Colorado . . ." {lists all or parts of 10 other high-altitude western states}.
I picked up my new SilverMaxima on May 15 with a full tank of what I was told was 91 octane premium (provided by the dealer) and almost 200 miles on the odometer. (The tank probably wasn't as full on this first tank as on the others.) Every time I filled up after that, I used 85 octane regular. I now have over 1,672 miles on her and I've only heard the engine knock (lightly) once, when I lugged it too much.
Here are my mileage results thru the last fill-up on July 2:
I've noticed that the computer screen tells me a different mileage (mpg) reading than when I calculate the average mileage for each tank of gas (city driving unless noted otherwise). On the third tank, I noticed that the computer also told me the average miles per hour from when I reset the computer (after each fill-up). Those average MPH readings are shown for the last 3 gasoline purchases:
TANK___MILES___COMPUTER___CALCULATED__TYPE DRIVING____Avg MPH
1st_____321_____19.0 mpg_____21.9 mpg____little highway
2nd_____365_____20.9 mpg_____26.1 mpg____some highway
3rd_____240_____22.1 mpg_____25.9 mpg____some highway____36 MPH
4th_____240_____22.1 mpg_____23.7 mpg____little highway_____22 MPH
5th_____307_____24.1 mpg_____24.9 mpg____little highway_____25 MPH
What can you conclude from this record:
- You get better mileage on the highway than around town.
- It appears that regular gets slightly better mileage than premium (or was it that the engine was still very tight because it wasn't broken-in, yet).
Again, the owners' manual has a comment {that needs interpretation}:
"However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency means better gasoline mileage and when you are very close to getting light spark knock, the engine is most efficient. You get that condition much more frequently using regular gasoline; thus better mileage with regular. This is all consistent with what I learned in the engine lab when earning my engineering degree in the early 60s.
I don't have an engine knock problem, and the car is very peppy. I can't tell the difference (driving the car) between premium and regular (other than the savings of 20 cents per gallon). But then I don't race everyone I see at each stop light. If I did, I'd probably burn premium.
In another week, I'll be gone for 6 weeks. I'll try and report my mileage experience when I return from this long road trip to the east.
07-03-2003, 04:39 AM
#31
Member
Thread Starter
Join Date: Jun 2003
Posts: 70
Re: Octane and Mileage -- The Numbers
Thank you so much! Posts like this are why I love this forum!
Originally posted by SilverMax_04
Some posters have asked for more science and less opinion. I'll give you mostly science (facts and numbers) with some opinion thrown in. But, before I give you the mileage numbers for my new SilverMaxima, I'd like to quote the owners' manual on octane:
"Use unleaded gasoline with an octane rating of at least 87 AKI (Anti-Knock Index). For improved performance . . . use unleaded premium gasoline with an octane rating of at least 91." This means regular gasoline will work fine and that premium will work somewhat better where improved performance is needed. There are really only two places where premium is "needed" -- if you experience severe engine knock, or if you're racing or otherwise calling for maximum acceleration frequently. Otherwise, save the 20 cents/gallon and buy regular.
I live in Colorado and normally drive at elevations between 6,000 feet and 7,200 feet above sea level. For this situation, the manual has the following information on gasoline octane:
"However, you may use unleaded gasoline with an octane rating as low as 85 AKI in high altitude areas [over 4,000 ft] such as Colorado . . ." {lists all or parts of 10 other high-altitude western states}.
I picked up my new SilverMaxima on May 15 with a full tank of what I was told was 91 octane premium (provided by the dealer) and almost 200 miles on the odometer. (The tank probably wasn't as full on this first tank as on the others.) Every time I filled up after that, I used 85 octane regular. I now have over 1,672 miles on her and I've only heard the engine knock (lightly) once, when I lugged it too much.
Here are my mileage results thru the last fill-up on July 2:
I've noticed that the computer screen tells me a different mileage (mpg) reading than when I calculate the average mileage for each tank of gas (city driving unless noted otherwise). On the third tank, I noticed that the computer also told me the average miles per hour from when I reset the computer (after each fill-up). Those average MPH readings are shown for the last 3 gasoline purchases:
TANK___MILES___COMPUTER___CALCULATED__TYPE DRIVING____Avg MPH
1st_____321_____19.0 mpg_____21.9 mpg____little highway
2nd_____365_____20.9 mpg_____26.1 mpg____some highway
3rd_____240_____22.1 mpg_____25.9 mpg____some highway____36 MPH
4th_____240_____22.1 mpg_____23.7 mpg____little highway_____22 MPH
5th_____307_____24.1 mpg_____24.9 mpg____little highway_____25 MPH
What can you conclude from this record:
- You get better mileage on the highway than around town.
- It appears that regular gets slightly better mileage than premium (or was it that the engine was still very tight because it wasn't broken-in, yet).
Again, the owners' manual has a comment {that needs interpretation}:
"However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency means better gasoline mileage and when you are very close to getting light spark knock, the engine is most efficient. You get that condition much more frequently using regular gasoline; thus better mileage with regular. This is all consistent with what I learned in the engine lab when earning my engineering degree in the early 60s.
I don't have an engine knock problem, and the car is very peppy. I can't tell the difference (driving the car) between premium and regular (other than the savings of 20 cents per gallon). But then I don't race everyone I see at each stop light. If I did, I'd probably burn premium.
In another week, I'll be gone for 6 weeks. I'll try and report my mileage experience when I return from this long road trip to the east.
Some posters have asked for more science and less opinion. I'll give you mostly science (facts and numbers) with some opinion thrown in. But, before I give you the mileage numbers for my new SilverMaxima, I'd like to quote the owners' manual on octane:
"Use unleaded gasoline with an octane rating of at least 87 AKI (Anti-Knock Index). For improved performance . . . use unleaded premium gasoline with an octane rating of at least 91." This means regular gasoline will work fine and that premium will work somewhat better where improved performance is needed. There are really only two places where premium is "needed" -- if you experience severe engine knock, or if you're racing or otherwise calling for maximum acceleration frequently. Otherwise, save the 20 cents/gallon and buy regular.
I live in Colorado and normally drive at elevations between 6,000 feet and 7,200 feet above sea level. For this situation, the manual has the following information on gasoline octane:
"However, you may use unleaded gasoline with an octane rating as low as 85 AKI in high altitude areas [over 4,000 ft] such as Colorado . . ." {lists all or parts of 10 other high-altitude western states}.
I picked up my new SilverMaxima on May 15 with a full tank of what I was told was 91 octane premium (provided by the dealer) and almost 200 miles on the odometer. (The tank probably wasn't as full on this first tank as on the others.) Every time I filled up after that, I used 85 octane regular. I now have over 1,672 miles on her and I've only heard the engine knock (lightly) once, when I lugged it too much.
Here are my mileage results thru the last fill-up on July 2:
I've noticed that the computer screen tells me a different mileage (mpg) reading than when I calculate the average mileage for each tank of gas (city driving unless noted otherwise). On the third tank, I noticed that the computer also told me the average miles per hour from when I reset the computer (after each fill-up). Those average MPH readings are shown for the last 3 gasoline purchases:
TANK___MILES___COMPUTER___CALCULATED__TYPE DRIVING____Avg MPH
1st_____321_____19.0 mpg_____21.9 mpg____little highway
2nd_____365_____20.9 mpg_____26.1 mpg____some highway
3rd_____240_____22.1 mpg_____25.9 mpg____some highway____36 MPH
4th_____240_____22.1 mpg_____23.7 mpg____little highway_____22 MPH
5th_____307_____24.1 mpg_____24.9 mpg____little highway_____25 MPH
What can you conclude from this record:
- You get better mileage on the highway than around town.
- It appears that regular gets slightly better mileage than premium (or was it that the engine was still very tight because it wasn't broken-in, yet).
Again, the owners' manual has a comment {that needs interpretation}:
"However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency means better gasoline mileage and when you are very close to getting light spark knock, the engine is most efficient. You get that condition much more frequently using regular gasoline; thus better mileage with regular. This is all consistent with what I learned in the engine lab when earning my engineering degree in the early 60s.
I don't have an engine knock problem, and the car is very peppy. I can't tell the difference (driving the car) between premium and regular (other than the savings of 20 cents per gallon). But then I don't race everyone I see at each stop light. If I did, I'd probably burn premium.
In another week, I'll be gone for 6 weeks. I'll try and report my mileage experience when I return from this long road trip to the east.
07-03-2003, 05:43 AM
#32
Senior Member
Join Date: Apr 2003
Posts: 1,282
Re: Octane and Mileage -- The Numbers
Originally posted by SilverMax_04
Some posters have asked for more science and less opinion. I'll give you mostly science (facts and numbers) with some opinion thrown in. But, before I give you the mileage numbers for my new SilverMaxima, I'd like to quote the owners' manual on octane:
"Use unleaded gasoline with an octane rating of at least 87 AKI (Anti-Knock Index). For improved performance . . . use unleaded premium gasoline with an octane rating of at least 91." This means regular gasoline will work fine and that premium will work somewhat better where improved performance is needed. There are really only two places where premium is "needed" -- if you experience severe engine knock, or if you're racing or otherwise calling for maximum acceleration frequently. Otherwise, save the 20 cents/gallon and buy regular.
I live in Colorado and normally drive at elevations between 6,000 feet and 7,200 feet above sea level. For this situation, the manual has the following information on gasoline octane:
"However, you may use unleaded gasoline with an octane rating as low as 85 AKI in high altitude areas [over 4,000 ft] such as Colorado . . ." {lists all or parts of 10 other high-altitude western states}.
I picked up my new SilverMaxima on May 15 with a full tank of what I was told was 91 octane premium (provided by the dealer) and almost 200 miles on the odometer. (The tank probably wasn't as full on this first tank as on the others.) Every time I filled up after that, I used 85 octane regular. I now have over 1,672 miles on her and I've only heard the engine knock (lightly) once, when I lugged it too much.
Here are my mileage results thru the last fill-up on July 2:
I've noticed that the computer screen tells me a different mileage (mpg) reading than when I calculate the average mileage for each tank of gas (city driving unless noted otherwise). On the third tank, I noticed that the computer also told me the average miles per hour from when I reset the computer (after each fill-up). Those average MPH readings are shown for the last 3 gasoline purchases:
TANK___MILES___COMPUTER___CALCULATED__TYPE DRIVING____Avg MPH
1st_____321_____19.0 mpg_____21.9 mpg____little highway
2nd_____365_____20.9 mpg_____26.1 mpg____some highway
3rd_____240_____22.1 mpg_____25.9 mpg____some highway____36 MPH
4th_____240_____22.1 mpg_____23.7 mpg____little highway_____22 MPH
5th_____307_____24.1 mpg_____24.9 mpg____little highway_____25 MPH
What can you conclude from this record:
- You get better mileage on the highway than around town.
- It appears that regular gets slightly better mileage than premium (or was it that the engine was still very tight because it wasn't broken-in, yet).
Again, the owners' manual has a comment {that needs interpretation}:
"However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency means better gasoline mileage and when you are very close to getting light spark knock, the engine is most efficient. You get that condition much more frequently using regular gasoline; thus better mileage with regular. This is all consistent with what I learned in the engine lab when earning my engineering degree in the early 60s.
I don't have an engine knock problem, and the car is very peppy. I can't tell the difference (driving the car) between premium and regular (other than the savings of 20 cents per gallon). But then I don't race everyone I see at each stop light. If I did, I'd probably burn premium.
In another week, I'll be gone for 6 weeks. I'll try and report my mileage experience when I return from this long road trip to the east.
Some posters have asked for more science and less opinion. I'll give you mostly science (facts and numbers) with some opinion thrown in. But, before I give you the mileage numbers for my new SilverMaxima, I'd like to quote the owners' manual on octane:
"Use unleaded gasoline with an octane rating of at least 87 AKI (Anti-Knock Index). For improved performance . . . use unleaded premium gasoline with an octane rating of at least 91." This means regular gasoline will work fine and that premium will work somewhat better where improved performance is needed. There are really only two places where premium is "needed" -- if you experience severe engine knock, or if you're racing or otherwise calling for maximum acceleration frequently. Otherwise, save the 20 cents/gallon and buy regular.
I live in Colorado and normally drive at elevations between 6,000 feet and 7,200 feet above sea level. For this situation, the manual has the following information on gasoline octane:
"However, you may use unleaded gasoline with an octane rating as low as 85 AKI in high altitude areas [over 4,000 ft] such as Colorado . . ." {lists all or parts of 10 other high-altitude western states}.
I picked up my new SilverMaxima on May 15 with a full tank of what I was told was 91 octane premium (provided by the dealer) and almost 200 miles on the odometer. (The tank probably wasn't as full on this first tank as on the others.) Every time I filled up after that, I used 85 octane regular. I now have over 1,672 miles on her and I've only heard the engine knock (lightly) once, when I lugged it too much.
Here are my mileage results thru the last fill-up on July 2:
I've noticed that the computer screen tells me a different mileage (mpg) reading than when I calculate the average mileage for each tank of gas (city driving unless noted otherwise). On the third tank, I noticed that the computer also told me the average miles per hour from when I reset the computer (after each fill-up). Those average MPH readings are shown for the last 3 gasoline purchases:
TANK___MILES___COMPUTER___CALCULATED__TYPE DRIVING____Avg MPH
1st_____321_____19.0 mpg_____21.9 mpg____little highway
2nd_____365_____20.9 mpg_____26.1 mpg____some highway
3rd_____240_____22.1 mpg_____25.9 mpg____some highway____36 MPH
4th_____240_____22.1 mpg_____23.7 mpg____little highway_____22 MPH
5th_____307_____24.1 mpg_____24.9 mpg____little highway_____25 MPH
What can you conclude from this record:
- You get better mileage on the highway than around town.
- It appears that regular gets slightly better mileage than premium (or was it that the engine was still very tight because it wasn't broken-in, yet).
Again, the owners' manual has a comment {that needs interpretation}:
"However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency means better gasoline mileage and when you are very close to getting light spark knock, the engine is most efficient. You get that condition much more frequently using regular gasoline; thus better mileage with regular. This is all consistent with what I learned in the engine lab when earning my engineering degree in the early 60s.
I don't have an engine knock problem, and the car is very peppy. I can't tell the difference (driving the car) between premium and regular (other than the savings of 20 cents per gallon). But then I don't race everyone I see at each stop light. If I did, I'd probably burn premium.
In another week, I'll be gone for 6 weeks. I'll try and report my mileage experience when I return from this long road trip to the east.
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