Gasoline facts
05-17-2005, 11:00 PM
#21
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Wow, I feel like I just went to a lecture on gasoline. I had been worried because I can't find a gas station in Springfield, MO that sells 93 octane. Not so worried now. Great information, this forum is awesome!
05-17-2005, 11:09 PM
#22
Drifting
Octane
[QUOTE=need-for-speed]Great post LDB. 
I must agree with the others that octane requirements are reduced with altitude. Why is it that as you get into the higher altitudes, the octane rating of the "locally sold" fuel is lower?[/QUOTE
I agree.. I was once somewhere by Pike's Peak and i had to fill up gas and the regular unleaded was an 85 Octane...
I blew me away because I've never seen anything lower than an 87 everywhere I go.
Now my question is if I live in Pike's Peak area (peak elevation is about 14,000 Feet) would my C6 benifit by filling it with 85 Octane??
I must agree with the others that octane requirements are reduced with altitude. Why is it that as you get into the higher altitudes, the octane rating of the "locally sold" fuel is lower?[/QUOTEI agree.. I was once somewhere by Pike's Peak and i had to fill up gas and the regular unleaded was an 85 Octane...
I blew me away because I've never seen anything lower than an 87 everywhere I go.Now my question is if I live in Pike's Peak area (peak elevation is about 14,000 Feet) would my C6 benifit by filling it with 85 Octane??
05-18-2005, 06:30 AM
#23
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Originally Posted by LDB
When you buy from the grocery store, or Wal-Mart, or a convenience store, you are much more exposed. Some of the time, those places buy from the majors, and their gas is perfectly OK. But all too often, they buy on the spot market, the cheapest stuff that happens to be floating by on a barge.
05-18-2005, 08:33 AM
#24
Drifting
Thread Starter
Comments continue about high altitude octane. I threw that comment in mostly as a gratuitous, here’s a case where buying extra high octane might make sense. I know that we often get comments from consumers complaining about knock in vacations to the mountains. Perhaps it’s due to, as one reader mentioned, less high octane fuel being available in the Rockies. Or perhaps because of long uphill grades in mountainous areas, octane needs are higher for the hill climbing part, not the actual high altitude part. My actual position in my oil company is running refineries, so it’s true that I am familiar with fuel quality needs. But I’m not an actual engine testing engineer, so it’s possible that I have misinterpreted this specific aspect of things. I’ll check with our engine testing people and get back to you. Most of them are off at a conference this week, so it probably won’t be right away.
There was also a comment about everyone taking gasoline from the same pipeline, so it’s all the same. As I pointed out in the original post, sometimes that’s true. It depends on the area. But the fact remains, with a major, you know where it’s coming from. With others, you don’t. Thus risk is higher in return for the lower price.
Another post said that Shell gasoline caused the fuel gauge problems. That’s partially true, and a good example of a comment in my original post, saying that everyone including the majors occasionally has a quality lapse. But they stood behind it and corrected the problems, which were well documented in industry as relating to the learning curve of starting up facilities to make ultra low sulfur gasoline. And there have been many non-Shell fuel gauge issues as well. The Shell incident only applies to gasoline in the southeast US for a very brief period last year. The current issues with C6 gas gauges being mentioned on the forum is a completely different problem.
There was also a comment about everyone taking gasoline from the same pipeline, so it’s all the same. As I pointed out in the original post, sometimes that’s true. It depends on the area. But the fact remains, with a major, you know where it’s coming from. With others, you don’t. Thus risk is higher in return for the lower price.
Another post said that Shell gasoline caused the fuel gauge problems. That’s partially true, and a good example of a comment in my original post, saying that everyone including the majors occasionally has a quality lapse. But they stood behind it and corrected the problems, which were well documented in industry as relating to the learning curve of starting up facilities to make ultra low sulfur gasoline. And there have been many non-Shell fuel gauge issues as well. The Shell incident only applies to gasoline in the southeast US for a very brief period last year. The current issues with C6 gas gauges being mentioned on the forum is a completely different problem.
05-18-2005, 12:24 PM
#28
Safety Car
Originally Posted by LDB
..... Or perhaps because of long uphill grades in mountainous areas, octane needs are higher for the hill climbing part, not the actual high altitude part. .
I live a 4500 feet and have yet to experience any pinging using 1 grade lower fuel than recommended. BUT I most certainly have experienced pinging when I dropped altitude and still had the lower octane fuel. (Reno to Sacramento is only 125 miles). So I usually fill up with premium if I know I I am going to run at low altitude.
05-18-2005, 07:15 PM
#31
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CI 1-4-5-8-9-10 Vet
St. Jude Donor '03,'04,'05,'07,08,'09,'10,’17
Originally Posted by JFTaylor
LDB,
Presuming I always use Exxon, are any after market additives worth the expense?
Presuming I always use Exxon, are any after market additives worth the expense?
05-18-2005, 10:05 PM
#32
Pro
Plese give your comments about the risk of cancer or other health issues regarding repeated contact or inhilation of gas or fumes when filling our cars at the gas station?
I would assume 87, 91 or 93 octance are equally toxic?
Also, there seems to be about a $0.10/gallon difference in price between grades... is that a marketing game or is there that much additional expense with the higher octane gasoline?
Thank you for the insight.
PS: I suspect the pinging at high altitudes going up hills is related to the fact that the engine may be running hotter and working harder with the continuos load and thus ignites "sooner" .
I would assume 87, 91 or 93 octance are equally toxic?
Also, there seems to be about a $0.10/gallon difference in price between grades... is that a marketing game or is there that much additional expense with the higher octane gasoline?
Thank you for the insight.
PS: I suspect the pinging at high altitudes going up hills is related to the fact that the engine may be running hotter and working harder with the continuos load and thus ignites "sooner" .
05-19-2005, 12:23 AM
#34
Team Owner
Is Arco gas one of the fuels to avoid like other no name brands. Arco well known.
Originally Posted by LDB
Lots of gasoline comments lately. I’m an engineer for a major oil company, familiar with engine testing for performance, economy, and emissions. I think my company’s gasoline is slightly better than other majors, but I’m not going to use the forum for advertising. Instead, I’ll make a few points about what you should look for in a gasoline. If you do that, my company will get more than an average share of your business.
Octane is generally misunderstood. High octane gasoline isn’t more powerful, it simply offers better resistance to engine knock. Lower than needed octane is a big penalty from knocking and/or spark retard, but higher than needed octane gives no benefits. Sounds odd, but it’s true as described below. Premium gasoline does have some benefits even to a car designed for regular, but those benefits aren’t from octane. They are from some other characteristics which are described at the very end, DI and additives. Let’s talk octane first.
Two main factors set octane requirement: compression ratio and spark advance. Compression ratio is a design feature of the engine, with higher ratios giving better performance, but also requiring higher octane rating. Corvettes need premium gasoline because they are high compression ratio, which requires high octane. Best performance in any given engine is at a particular spark advance, and going in either direction makes poorer performance. But while it costs performance, less than optimum spark advance does have the advantage of lowering octane requirement. So your knock sensor can compensate for low octane fuel by retarding the spark, at a cost in performance. But the reverse is not true. Once octane is high enough to allow optimum spark advance, more octane doesn’t help, because greater than optimum spark advance does not increase performance.
The Corvette gasoline spec is 91. There is some variability in engine response depending on a myriad of other characteristics including engine age, but it’s safe to say that benefits of 93 versus 91 are small, and 94 versus 93 are nil. You can make similar comments about the benefits of greater than 87 octane in a normal car. Its compression ratio is lower, so it can get to optimum spark advance on 87 octane. Running 93 octane will not help turn it into a Corvette, because it doesn’t have the compression ratio to utilize the higher octane.
Bottom line on octane is that benefit of being over manufacturers recommendation is slim to none. The only three things that can cause you to get significant benefit from going higher are: 1) a 100,000 mile engine probably needs a couple of numbers more than new due to various irregularities in an old engine, 2) if you live at high altitude, a couple of numbers over normal spec are usually needed, or 3) if you do major engine modifications to raise compression ratio.
Other issues are a detergent additive package for valve and injector cleanliness, a reliable quality control system, and good DI, drivability index, a measure of how well the fuel evaporates. All majors are roughly equivalent in those areas, and most premium gasolines have more detergent and better DI than most regulars. There are shades of gray differences in additives, but once you are with a major oil company, you need careful tests to see them. All majors (including my own) have had quality control lapses, usually with sulfur (causes odor, emissions, and gas gauge problems), particulates (plugs filters prematurely), and/or water (the worst of all, and can devastate an engine, but this one is almost unheard of with the majors). But when the rare lapse does occur, we quickly correct the problem, including any damage it may have caused. When you buy from the grocery store, or Wal-Mart, or a convenience store, you are much more exposed. Some of the time, those places buy from the majors, and their gas is perfectly OK. But all too often, they buy on the spot market, the cheapest stuff that happens to be floating by on a barge. This gives you higher probability of a serious quality control incident, and also exposes you to poor additives and DI. In the short term, you’d never notice lack of detergent additives, but over time, you engine will foul. DI symptoms are subtle, mostly a rough warm up period, but poor DI also tends to foul the engine, especially if it is short on detergent. So you have to ask yourself, do you want to fuel a $50,000 car from the lowest bidder.
Anyway, at the very end of this tome, I’d advise you to set you minimum standard as being at least recommended octane, from one of the majors. Once you are at that point, differences become small. Does 93 versus 91 or 94 versus 93 make much difference? Probably not, unless you live in the mountains or have an aging engine. Is premium worth it in your regular car for the slightly higher additive concentration and slightly better DI if you don’t need the octane? You have to make that decision. There are benefits, but you are into small stuff. It’s kind of like Mobil 1 versus normal oil. Sure, Mobil 1 is very slightly better. It’s also $4 versus $1 per quart. But that’s another long post, and I’m out of energy for now.
Octane is generally misunderstood. High octane gasoline isn’t more powerful, it simply offers better resistance to engine knock. Lower than needed octane is a big penalty from knocking and/or spark retard, but higher than needed octane gives no benefits. Sounds odd, but it’s true as described below. Premium gasoline does have some benefits even to a car designed for regular, but those benefits aren’t from octane. They are from some other characteristics which are described at the very end, DI and additives. Let’s talk octane first.
Two main factors set octane requirement: compression ratio and spark advance. Compression ratio is a design feature of the engine, with higher ratios giving better performance, but also requiring higher octane rating. Corvettes need premium gasoline because they are high compression ratio, which requires high octane. Best performance in any given engine is at a particular spark advance, and going in either direction makes poorer performance. But while it costs performance, less than optimum spark advance does have the advantage of lowering octane requirement. So your knock sensor can compensate for low octane fuel by retarding the spark, at a cost in performance. But the reverse is not true. Once octane is high enough to allow optimum spark advance, more octane doesn’t help, because greater than optimum spark advance does not increase performance.
The Corvette gasoline spec is 91. There is some variability in engine response depending on a myriad of other characteristics including engine age, but it’s safe to say that benefits of 93 versus 91 are small, and 94 versus 93 are nil. You can make similar comments about the benefits of greater than 87 octane in a normal car. Its compression ratio is lower, so it can get to optimum spark advance on 87 octane. Running 93 octane will not help turn it into a Corvette, because it doesn’t have the compression ratio to utilize the higher octane.
Bottom line on octane is that benefit of being over manufacturers recommendation is slim to none. The only three things that can cause you to get significant benefit from going higher are: 1) a 100,000 mile engine probably needs a couple of numbers more than new due to various irregularities in an old engine, 2) if you live at high altitude, a couple of numbers over normal spec are usually needed, or 3) if you do major engine modifications to raise compression ratio.
Other issues are a detergent additive package for valve and injector cleanliness, a reliable quality control system, and good DI, drivability index, a measure of how well the fuel evaporates. All majors are roughly equivalent in those areas, and most premium gasolines have more detergent and better DI than most regulars. There are shades of gray differences in additives, but once you are with a major oil company, you need careful tests to see them. All majors (including my own) have had quality control lapses, usually with sulfur (causes odor, emissions, and gas gauge problems), particulates (plugs filters prematurely), and/or water (the worst of all, and can devastate an engine, but this one is almost unheard of with the majors). But when the rare lapse does occur, we quickly correct the problem, including any damage it may have caused. When you buy from the grocery store, or Wal-Mart, or a convenience store, you are much more exposed. Some of the time, those places buy from the majors, and their gas is perfectly OK. But all too often, they buy on the spot market, the cheapest stuff that happens to be floating by on a barge. This gives you higher probability of a serious quality control incident, and also exposes you to poor additives and DI. In the short term, you’d never notice lack of detergent additives, but over time, you engine will foul. DI symptoms are subtle, mostly a rough warm up period, but poor DI also tends to foul the engine, especially if it is short on detergent. So you have to ask yourself, do you want to fuel a $50,000 car from the lowest bidder.
Anyway, at the very end of this tome, I’d advise you to set you minimum standard as being at least recommended octane, from one of the majors. Once you are at that point, differences become small. Does 93 versus 91 or 94 versus 93 make much difference? Probably not, unless you live in the mountains or have an aging engine. Is premium worth it in your regular car for the slightly higher additive concentration and slightly better DI if you don’t need the octane? You have to make that decision. There are benefits, but you are into small stuff. It’s kind of like Mobil 1 versus normal oil. Sure, Mobil 1 is very slightly better. It’s also $4 versus $1 per quart. But that’s another long post, and I’m out of energy for now.
05-19-2005, 03:44 AM
#35
Originally Posted by TedG
Now that part make a lot of sense.
I live a 4500 feet and have yet to experience any pinging using 1 grade lower fuel than recommended. BUT I most certainly have experienced pinging when I dropped altitude and still had the lower octane fuel. (Reno to Sacramento is only 125 miles). So I usually fill up with premium if I know I I am going to run at low altitude.
I live a 4500 feet and have yet to experience any pinging using 1 grade lower fuel than recommended. BUT I most certainly have experienced pinging when I dropped altitude and still had the lower octane fuel. (Reno to Sacramento is only 125 miles). So I usually fill up with premium if I know I I am going to run at low altitude.
05-19-2005, 07:51 AM
#36
Drifting
Thread Starter
Thanks for the continuing interest.
Answers to a few other questions since my last post. There is little or nothing to be gained from aftermarket additives over and above the additives in a good gasoline. As to the recent “top tier” stuff, I’d characterize that as being somewhat similar to the synthetics discussion in my “oil facts” post. Directionally, they can be shown to be a bit better. But when you start with something that is very good, there isn’t much room to improve. The big risk area is in the reverse direction, if you go with the bargain basement guys where there is non trivial risk of getting bad stuff.
Cost of generating octane in a refinery is about 1 cent per octane gallon in most of the US, and nearly double that in California. The reason it is more expensive in California is that CARB (California Air Resources Board) mandates low olefins content and low end point, both of which cost octane. So we have to get it back somewhere, and as you go further and further, each additional octane you try to find costs more and more. Benefits of the low olefins and end point specs are debatable, but I don’t want to get into that debate. Clearly, the specs give a directional benefit, but just as clearly, CARB’s claims of the degree of benefit are absurd. But the two specs together explain about 15 cents per gallon of the reason gasoline costs more in California than anywhere else.
From the above paragraph, you can of course, alertly deduce that more profit is made on premium than on regular. The octane costs 6 cents, and other aspects cost another penny or two, but the cost of making it is nowhere near the 20 cents or so that it usually commands on the street.
On toxicity, premium is directionally a smidgen more toxic than regular. That because aromatics are the most toxic, and they are also the highest octane. To get its higher octane, premium is slightly higher in aromatics than regular. But the difference is very slight.
Answers to a few other questions since my last post. There is little or nothing to be gained from aftermarket additives over and above the additives in a good gasoline. As to the recent “top tier” stuff, I’d characterize that as being somewhat similar to the synthetics discussion in my “oil facts” post. Directionally, they can be shown to be a bit better. But when you start with something that is very good, there isn’t much room to improve. The big risk area is in the reverse direction, if you go with the bargain basement guys where there is non trivial risk of getting bad stuff.
Cost of generating octane in a refinery is about 1 cent per octane gallon in most of the US, and nearly double that in California. The reason it is more expensive in California is that CARB (California Air Resources Board) mandates low olefins content and low end point, both of which cost octane. So we have to get it back somewhere, and as you go further and further, each additional octane you try to find costs more and more. Benefits of the low olefins and end point specs are debatable, but I don’t want to get into that debate. Clearly, the specs give a directional benefit, but just as clearly, CARB’s claims of the degree of benefit are absurd. But the two specs together explain about 15 cents per gallon of the reason gasoline costs more in California than anywhere else.
From the above paragraph, you can of course, alertly deduce that more profit is made on premium than on regular. The octane costs 6 cents, and other aspects cost another penny or two, but the cost of making it is nowhere near the 20 cents or so that it usually commands on the street.
On toxicity, premium is directionally a smidgen more toxic than regular. That because aromatics are the most toxic, and they are also the highest octane. To get its higher octane, premium is slightly higher in aromatics than regular. But the difference is very slight.
05-19-2005, 08:43 AM
#37
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St. Jude Donor '06
OH No Mr Speed
Originally Posted by need-for-speed
7-up is an excellent additive to Baccardi
Guess I'm more a purist. Coke w/rum
05-19-2005, 09:09 AM
#38
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I think I remember reading that 87 octane fuel has more BTU's than 93 does. I know my airplane has an STC to run 87 instead of 100 low lead and it's supposed to have more power (BTU's) than the 100 low lead does.
J
J
