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JT


Registered: 02/28/07
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Loc: athens
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thinking about switching to premium gas...
#14074413 - 03/06/11 06:52 AM (12 years, 10 months ago) |
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as the price of gas keeps rising, i keep thinking about switching to the more expensive premium gas. sounds crazy, right? but hear me out...
no matter how high the price of regular goes, premium is always only ten cents more per gallon. proportionally, this ten cent difference is becoming less in regards to the overall cost of gas. going to premium didn't make much sense for the average driver when gas was only $2.00. the extra 10 or 20 cents is 5-10% more expensive, respectively. however, at $3.50 or soon to be $4.00, that percentage is halved.
if i go from 87 to the 94 rating, my that's about a 12% increase. so would i get 12% better mileage? i'm not sure if that's the way it works, but if it is, it makes sense to spend 2-3% more for the better stuff. i'd be saving money in the long run.
thoughts/comments? i'm probably missing something crucial here.
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badchad
Mad Scientist

Registered: 03/02/05
Posts: 13,372
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Re: thinking about switching to premium gas... [Re: JT]
#14074436 - 03/06/11 07:02 AM (12 years, 10 months ago) |
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No. You won't get 12% better mileage. You'll just be spending more money.
-------------------- ...the whole experience is (and is as) a profound piece of knowledge. It is an indellible experience; it is forever known. I have known myself in a way I doubt I would have ever occurred except as it did. Smith, P. Bull. Menninger Clinic (1959) 23:20-27; p. 27. ...most subjects find the experience valuable, some find it frightening, and many say that is it uniquely lovely. Osmond, H. Annals, NY Acad Science (1957) 66:418-434; p.436
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Yacub
Psychedelic Redneck



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Re: thinking about switching to premium gas... [Re: JT]
#14074437 - 03/06/11 07:02 AM (12 years, 10 months ago) |
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I don't think that octane has anything to do with gas mileage. If your car runs good on whatever octane you're using, you should just stick with it.
Quote:
octane number of a fuel is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.[1] This does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties. Because some fuels are more knock-resistant than iso-octane, The the definition has been extended to allow for octane numbers higher than 100.
Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.
http://en.wikipedia.org/wiki/Octane_rating
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Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
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Re: thinking about switching to premium gas... [Re: badchad]
#14074440 - 03/06/11 07:03 AM (12 years, 10 months ago) |
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You won't get 12% better mileage. It's possible that over the life of the car, you'd get better performance if you used the right gas all the time.
Mine calls for mid-grade. Owner's manual says premium is too rich, don't use it.
-------------------- You make it all possible. Doesn't it feel good?
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JT


Registered: 02/28/07
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Re: thinking about switching to premium gas... [Re: Doc_T]
#14074447 - 03/06/11 07:05 AM (12 years, 10 months ago) |
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alright, well so much for that idea. yeah reading up on octane ratings now, guess it has nothing to do with mileage
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Prisoner#1
Even Dumber ThanAdvertized!


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Re: thinking about switching to premium gas... [Re: JT]
#14074449 - 03/06/11 07:06 AM (12 years, 10 months ago) |
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there's no point in running anything more than standard unleaded (if you can find leaded and dont have a catalytic converter, I'd go that route), premium is fine if you're running a high performance engine but you will only see a few HP in gain, no added mileage
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Yacub
Psychedelic Redneck



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Also... [Re: Yacub]
#14074457 - 03/06/11 07:10 AM (12 years, 10 months ago) |
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http://home.comcast.net/~ndberg/premiumgas.html
Premium gas - better or scam? When I moved to Colorado, it surprised me to see that the 'low grade' gasoline was 85 octane, where it was 87 in most other places. My vehicle's owners manual said to use 87 or above, so I thought I had to use "mid-grade", which was, well, 87 octane. But, then I started hearing rumors that "85 in Colorado is the same as 87 at sea level", so I decided to investigate further.
Side note: in the US, we use the (R+M)/2 method of determining octane values, which is different than other countries. So the typical 85/87/91 octane in Colorado may seem low, but they are not as bad as it might seem at first glance. I don't know much about the computation methods, so I won't go into detail here.
A quick tutorial on the relevant parts of how a gasoline engine works.. First, a piston in a cylinder moves down, creating a vacuum in that cylinder. The fuel/air mixture is sucked into the cylinder via an open 'intake valve(s)'. Then the intake valve(s) closes, and the piston moves up in the cylinder, compressing the fuel/air mixture (note: which also heats it up). Then, at the proper moment, a spark plug fires which ignites the compressed fuel/air mixture, which forces the piston down. The piston then moves back up, forcing the exhaust out the now open exhaust valve(s).
So, what is Octane? Answer: it is a knock inhibitor. What is knock? Knock is that 'pinging' noise you sometimes hear in some cars when accelerating. What is happening is that the fuel/air mixture in the engine's cylinders is actually igniting before the spark plug fires. Another name is preignition. Basically, the fuel/air mixture is getting to a high enough temperature due to the compression of the fuel/air in the cylinder to ignite on its own. Octane increases the ignition temperature, making it such that it is less likely to ignite until the spark plug fires.
Thus, higher octane implies 'higher ignition temperature' or 'higher flash point'.
This explains why many sports cars and high-end cars require high octane fuel. Cars that have high compression ratio engines must in-turn require high octane fuel. The more an engine compresses the fuel/air mixture, the higher the temperature gets inside the cylinders, and in-turn the more prone to pre-ignition/knock.
So, why does Colorado have lower octane fuel available? Answer: the altitude. At 5,000 feet, there is less air available to the engine. There being less fuel/air to compress in the cylinder means that the temperature does not get as high in the engine's cylinders, thus not as much octane is required. For driving in the mountains where the elevation is even higher, one actually needs lower octane.
Why is it called premium? Beats me. All reputable refineries put the same detergents and additives in all of their grades. The only difference is octane. There is nothing "premium" about it as far as I can tell. If you don't need it, you won't get any benefit. The recommendation I've heard most often is to go by the recommended octane level as specified in your vehicles owner's manual. If you live at 5,000 feet, you can safely subtract 2 from that recommended value. You can tell if you go too low, as you will start to hear your engine knocking or pinging. If you do, simply move up a grade. If you never hear knock, there is no reason to move up a grade.
Why don't diesels have grades? Diesels work slightly differently from gasoline engines. A gasoline engine sucks in a fuel/air mixture, then compresses it, then a spark plug fires to ignite it. A diesel sucks in air (with no chance of pre-ignition), compresses the air (which also heats it), then injects the fuel into the already compressed cylinder. The air is hot enough and diesel fuel has a low enough ignition point that it now ignites. That's also explains why many diesels have "glow plugs", they are there to warm the cylinders before the engine has had time to warm up to normal operating temperature.
My understanding is that modern engine control computers are constantly tuning an engine as they drive. They also sort of remember what seems to work best. So, it is best to always use the same brand and octane of gasoline each fill-up. If you do switch, it may take a few tanks for your vehicles computer to adjust the engine to work optimally with the new gasoline. Have you heard the ads "try us for 5 tanks"? Now you know why... This data could be out of date, modern vehicle computers may adjust more quickly to changes. I just don't know.
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iluvfungi



Registered: 06/17/09
Posts: 1,488
Loc: Oakland, CA USA
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Re: thinking about switching to premium gas... [Re: JT]
#14074458 - 03/06/11 07:12 AM (12 years, 10 months ago) |
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Quote:
JT said: as the price of gas keeps rising, i keep thinking about switching to the more expensive premium gas. sounds crazy, right? but hear me out...
no matter how high the price of regular goes, premium is always only ten cents more per gallon. proportionally, this ten cent difference is becoming less in regards to the overall cost of gas. going to premium didn't make much sense for the average driver when gas was only $2.00. the extra 10 or 20 cents is 5-10% more expensive, respectively. however, at $3.50 or soon to be $4.00, that percentage is halved.
if i go from 87 to the 94 rating, my that's about a 12% increase. so would i get 12% better mileage? i'm not sure if that's the way it works, but if it is, it makes sense to spend 2-3% more for the better stuff. i'd be saving money in the long run.
thoughts/comments? i'm probably missing something crucial here.
Unless the car is specifically designed for Premium, like a turbo or a chipped car, performance vehicle, no point exists.
Besides toulene is way better at increasing octane, even in small amounts. The valve seals in the engine eventually wear out if you use a lot over a long time. But even an idiot can replace those and pull off a engine head, replace a timing belt.
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Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
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Re: Also... [Re: Yacub]
#14074460 - 03/06/11 07:12 AM (12 years, 10 months ago) |
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Huh.
-------------------- You make it all possible. Doesn't it feel good?
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starfire_xes
I Am 'They'



Registered: 10/24/09
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Re: thinking about switching to premium gas... [Re: JT]
#14074581 - 03/06/11 08:18 AM (12 years, 10 months ago) |
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you will probably get less mileage on premium. Thats because, premium is designed so it doesn't detonate early, and it has less energy. Think of alcohol as a premium additive, alcohol is good for boosting octane but it results in less energy delivered, therefore mileage goes downs. And most premiums are alcohol based now since they don't use lead.
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Doc_T
Random Dude




Registered: 03/06/09
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Loc: Colorado
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074596 - 03/06/11 08:24 AM (12 years, 10 months ago) |
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Quote:
starfire_xes said: And most premiums are alcohol based now since unrelated fact: they don't use lead.
Lead != octane
-------------------- You make it all possible. Doesn't it feel good?
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starfire_xes
I Am 'They'



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Re: thinking about switching to premium gas... [Re: Doc_T]
#14074605 - 03/06/11 08:27 AM (12 years, 10 months ago) |
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? Lead used to be put in gasoline to increase the octane rating. Now they use alcohol.
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IF THE NEIGHBORS COMPLAIN BECAUSE THE MUSIC'S TOO LOUD, TURN IT UP SO YOU CAN'T HEAR THEM BITCH
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Prisoner#1
Even Dumber ThanAdvertized!


Registered: 01/22/03
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Re: thinking about switching to premium gas... [Re: iluvfungi]
#14074619 - 03/06/11 08:35 AM (12 years, 10 months ago) |
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Quote:
iluvfungi said:
Besides toulene is way better at increasing octane
Toluene
gimme my $5
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Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074626 - 03/06/11 08:36 AM (12 years, 10 months ago) |
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Quote:
starfire_xes said: ? Lead used to be put in gasoline to increase the octane rating. Now they use alcohol.
Lead was used to reduce engine wear. Alcohol is used as a filler, not a booster.
-------------------- You make it all possible. Doesn't it feel good?
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Prisoner#1
Even Dumber ThanAdvertized!


Registered: 01/22/03
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074629 - 03/06/11 08:37 AM (12 years, 10 months ago) |
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Quote:
starfire_xes said: ? Lead used to be put in gasoline to increase the octane rating. Now they use alcohol.
it was also the best top cylinder lubricant available, since they stopped adding lead to fuels in the US car makers had to move to hardened valve seats, usually induction hardened but in older cars an insert had to be added
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Patlal
You ask too many questions



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Re: thinking about switching to premium gas... [Re: Prisoner#1]
#14074633 - 03/06/11 08:38 AM (12 years, 10 months ago) |
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OP
I think you finally went crazy. Mission achieved!
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starfire_xes
I Am 'They'



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Re: thinking about switching to premium gas... [Re: Doc_T]
#14074642 - 03/06/11 08:41 AM (12 years, 10 months ago) |
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You are wrong. Lead was 'anti-knock' compounds used to increase the octane rating. The myth was that it was to 'lubricate the valves' or something, which isn't really true. Knocking will cause burnt valves and other engine damage.
"Anti-knock agents may be added to further increase the octane rating. Tetraethyl lead, Pb(C2H5)4, was one such agent, which was added to gas at the rate of up to 2.4 grams per gallon of gasoline. The switch to unleaded gasoline has required the addition of more expensive compounds, such as aromatics and highly branched alkanes, to maintain high octane numbers."
Here is the source: http://chemistry.about.com/cs/howthingswork/a/aa070401a_2.htm
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JT


Registered: 02/28/07
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Loc: athens
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Re: thinking about switching to premium gas... [Re: Patlal]
#14074649 - 03/06/11 08:44 AM (12 years, 10 months ago) |
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Huh?
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Doc_T
Random Dude




Registered: 03/06/09
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074657 - 03/06/11 08:46 AM (12 years, 10 months ago) |
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So if I get this, alcohol is a substitute for the 'more expensive compounds' which are a substitute for lead, which was/is an anti-knocking agent, aka octane booster??
I'm old enough to remember leaded gas, but not old enough to have bought it. Kinda cool in an off-topic sort of way.
-------------------- You make it all possible. Doesn't it feel good?
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starfire_xes
I Am 'They'



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Re: thinking about switching to premium gas... [Re: Doc_T]
#14074671 - 03/06/11 08:50 AM (12 years, 10 months ago) |
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yes, that is how I understand it. I remember right before they changed to unleaded, the octane ratings at the pump would be like 102~110. Because a lot of cars had high-compression engines in those days.
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Prisoner#1
Even Dumber ThanAdvertized!


Registered: 01/22/03
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074682 - 03/06/11 08:51 AM (12 years, 10 months ago) |
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Quote:
starfire_xes said: You are wrong. Lead was 'anti-knock' compounds used to increase the octane rating. The myth was that it was to 'lubricate the valves' or something, which isn't really true. Knocking will cause burnt valves and other engine damage.
except it is true
http://en.wikipedia.org/wiki/Gasoline#Lead
Quote:
A side effect of the lead additives was protection of the valve seats from erosion. Many classic cars' engines have needed modification to use lead-free fuels since leaded fuels became unavailable. However, "Lead substitute" products are also produced and can sometimes be found at auto parts stores. These were scientifically tested and some were approved by the Federation of British Historic Vehicle Clubs at the UK's Motor Industry Research Association (MIRA) in 1999.[19]
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starfire_xes
I Am 'They'



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Re: thinking about switching to premium gas... [Re: Prisoner#1]
#14074688 - 03/06/11 08:52 AM (12 years, 10 months ago) |
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OK Pris, so we are both right. That's once in a row.
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IF THE NEIGHBORS COMPLAIN BECAUSE THE MUSIC'S TOO LOUD, TURN IT UP SO YOU CAN'T HEAR THEM BITCH
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Prisoner#1
Even Dumber ThanAdvertized!


Registered: 01/22/03
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Re: thinking about switching to premium gas... [Re: starfire_xes]
#14074700 - 03/06/11 08:56 AM (12 years, 10 months ago) |
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Quote:
starfire_xes said: yes, that is how I understand it. I remember right before they changed to unleaded, the octane ratings at the pump would be like 102~110. Because a lot of cars had high-compression engines in those days.
there were few places around here that carried 102 octane, most stopped in the 98 range and the 102+ was labeled as blue/racing fuel, still sold at the pumps for a short time now it's only available at the airport and through some racing outlets up to 110 octane
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Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
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Re: thinking about switching to premium gas... [Re: Prisoner#1]
#14074726 - 03/06/11 09:09 AM (12 years, 10 months ago) |
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Quote:
Prisoner#1 said: except it is true
http://en.wikipedia.org/wiki/Gasoline#Lead
ZOMG! Everybody is right all at once. Thread win for the win!
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RobMarley420
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Re: thinking about switching to premium gas... [Re: Doc_T]
#14074733 - 03/06/11 09:14 AM (12 years, 10 months ago) |
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I use premium gas, but only because my car needs it.
Cadillac Deville with V-8 Northstar engine.
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starfire_xes
I Am 'They'



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Re: thinking about switching to premium gas... [Re: Prisoner#1]
#14074736 - 03/06/11 09:14 AM (12 years, 10 months ago) |
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Quote:
Prisoner#1 said: there were few places around here that carried 102 octane, most stopped in the 98 range and the 102+ was labeled as blue/racing fuel, still sold at the pumps for a short time now it's only available at the airport and through some racing outlets up to 110 octane
In the southwest in the late 60's, gasoline ranged up to 110. At the pumps.
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IF THE NEIGHBORS COMPLAIN BECAUSE THE MUSIC'S TOO LOUD, TURN IT UP SO YOU CAN'T HEAR THEM BITCH
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