So I'm trying to figure out how much money I'm saving by using premium gasoline as opposed to mid-grade. Ok, maybe not "saving" but how much am I really paying for gas by using premium. Once regular gasoline got to around $4/gal if figured it was probably worth it to start using premium like I'm supposed to with my car. I've been doing this for the past 2 weeks or so and here's what I got so far:

Plus

Price: ~4.099
mi/gal: ~25.6

Premium

Price: ~4.199
mi/gal: ~29.3


I have a 13.3 gallon tank, lets use 12 gallons as the amount of gasoline I use since its a flat number.

Premium Fill-up: $50.39

Plus Fill-up: $49.18

When using Plus gas, I can go a total of 307.2 mi at a mileage rate of 25.6 mi/gal

When using Premium, I can go a total of 351.6 mi at a mileage rate of 29.3 mi/gal

that's a difference of 44.4 mi, and 3.7 mi/gal

if I divide my 351.6 mi from my Premium usage by the mileage rate of the Plus usage I get 13.73 gallons. Which I think means that by buying 12 gallons of Premium gas I'm getting the equivalent of 13.73 gallons of Plus gas.

If I divide the fill-up price for Premium ($50.39) by the 13.73 gallon equivalent of Plus, I get $3.669/gallon.

So essentially, by using premium gasoline in my car I'm actually buying gasoline for $3.67 a gallon instead of $4.20/gallon, saving ~$0.53/gallon over Plus (~$6.36 total per fill-up) while getting over an extra gallon's worth of performance.

Am I thinking about that the right way?

6/14/2008 1:46:33 PM

i'm not backing you up on the math, because you're overthinking it.

if your car does not need higher octane, you are wasting money by using it. however, if your car is designed to use high octane fuel, you should use it. if you don't, you will damage your engine and/or cause it to put out less power, and likely operate at reduced efficiency (the best case scenario is that the computer pulls timing to detune your engine for piss-fuel. at least this way you don't fuck your car up.)

6/14/2008 1:55:34 PM

v-power ftw.

6/14/2008 1:56:30 PM

Quote :

"Premium Fill-up: $50.39 Plus Fill-up: $49.18 When using Plus gas, I can go a total of 307.2 mi at a mileage rate of 25.6 mi/gal When using Premium, I can go a total of 351.6 mi at a mileage rate of 29.3 mi/gal"

Premium: 50.39/351.6 = ~$0.14/mile
Plus: 49.18/307.2 = ~$0.16/mile

I've been doing the same with my truck(well buying premium instead of regular) and getting similar results. GG

6/14/2008 2:01:37 PM

a lot of cars that are supposed to run on premium will run fine on regular

6/14/2008 2:04:02 PM

yeah i def. get better mileage by using premuim.

3+mpg more.

6/14/2008 2:09:53 PM

^^

like i said, in many cars, the knock sensor will cue the ECU to pull ignition timing. this prevents the engine from damaging itself, but your car will have less power, and quite possibly get worse fuel economy.

of course, if your car is older and doesn't have the ability to do this, you will fuck your engine up.

if your car only needs 87 octane, you gain nothing by putting 89 or 92/93 in it.


there MAY be some cars out there that specify high octane fuel that don't actually need it at all, but I'm not aware of them. that would be dumb on the part of the manufacturer, in my opinion.


long story short, use whatever fuel the manufacturer specifies.

6/14/2008 2:45:50 PM

Bingo.

I don't know why people try to argue this point constantly.

6/14/2008 2:48:32 PM

^tons of people claim to get better gas mileage and smoother engine operation from using premium gas. even when their cars make about 50hp/liter

6/14/2008 4:40:21 PM

Quote :

"there MAY be some cars out there that specify high octane fuel that don't actually need it at all, but I'm not aware of them. that would be dumb on the part of the manufacturer, in my opinion."

depends on what exactly you (or the mfg) mean...

http://www.edmunds.com/advice/fueleconomy/articles/106293/article.html

6/14/2008 8:13:09 PM

Quote :

"When using Plus gas, I can go a total of 307.2 mi at a mileage rate of 25.6 mi/gal When using Premium, I can go a total of 351.6 mi at a mileage rate of 29.3 mi/gal "

Do you really get 40 extra miles on premium? What type of car? What's the compression ratio?

The compression on most shitboxes is so low that you'd see no benefit with premium.

6/14/2008 8:41:12 PM

i'm gonna go out on a limb and say its a typical econo shitbox is 29 is the highest he's seeing ever.. my V8 lincoln LS gets that

but only on premium.. my numbers are almost exactly what yours are. on regular i get around 25 and on premium around 29..

6/14/2008 8:43:36 PM

^^^ that article says almost EXACTLY what i've said in this thread.

6/14/2008 9:05:14 PM

congratulations?

6/14/2008 9:07:46 PM

my maxima gets 3-4mpgs on premium than regular.

definitely worth it.

6/14/2008 9:28:47 PM

yep, you're thinking about it right.

about a month ago, a coworker and I were dicking around in Excel to determine breakeven points for Premium vs. Plus. At these prices its only about 1 mpg.

If your car gets just 1 mpg better on 1 grade of fuel better, its worth it to make the jump up.

6/15/2008 8:33:37 AM

Its funny how people who know a bit about cars know shit about chemistry and math.

[Edited on June 15, 2008 at 11:44 AM. Reason : a]

6/15/2008 11:43:48 AM

I find that the opposite is generally true, especially once you get beyond the level of the shadetree mechanic.

6/15/2008 1:12:43 PM

The fact that they call it premium confuses people.

I think they feel its "more pure" or some such nonsense.

6/15/2008 1:43:34 PM

To offer a corollary if I may. Does anyone know or have they thought to see if premium gas from one station is better than that from another? As in is BP better than Sheetz? Also, how can you be sure you are actually getting premium when you pay for it and push the button when it comes from the pumps with only one hose?

6/15/2008 3:42:59 PM

Quote :

"It should be noted that octane rating does not relate to the energy content of the fuel (see heating value), nor the speed at which the flame initiated by the spark plug propagates across the cylinder. It is only a measure of the fuel's resistance to autoignition. It is for this reason that one highly branched form, or isomer, of octane (2,2,4-trimethylpentane) has (by definition) an octane rating of 100, whereas n-octane (see octane), which has a linear arrangement of the 8 carbon atoms, has an octane rating of -10, even though the two fuels have exactly the same chemical formula and virtually identical heating values and flame speeds. "

from Wiki



as with Duke, if the car is factory spec'd for regular, premium provides no benefit. Cars that require premium (or have been modified to necessitate higher octane fuel) should be run with premium or higher.

6/15/2008 3:55:46 PM

^^I'd say without even really thinking that yes BP is better than Sheetz. There is a minimum fuel standard requirement that all gasoline sellers must meet. There is also a voluntary higher standard that only a few meet. As far as I know only Exxon, Shell, & BP meet the higher standard.

As a general rule I stay away from no name fuels, there's no telling where it came from. I also stay away from Citgo & Lukoil for political reasons.

^^regarding whats coming out when there's only one hose...the gasoline is tested routinely by inspectors for such things.

[Edited on June 15, 2008 at 4:12 PM. Reason : k]

6/15/2008 4:11:53 PM

^^^ my understanding is that the only real difference is in additive/detergent packages, and I think that federal (and/or state??) regulations have tightened up that difference to a large extent in recent years (both across different brands and different grades).

as far as the pushbutton-type pumps, they are inspected periodically. a few people with very high performance motorcycles are even picky about not going to those, because they worry they might get a splash of 87 octane in with their high-test (like a leftover bit from the last person to use the pump). from what i've read, though, the pumps are designed so that doesn't happen. also, a few ounces won't make any difference on a car. the people who are (in my opinion, needlessly) worried are thinking about motorcycles where the tank only holds a few gallons.

[Edited on June 15, 2008 at 5:32 PM. Reason : ^ok. i still wouldn't worry too much about it...maybe go name-brand at least every 2 or 3 fills.]

6/15/2008 5:31:22 PM

let me throw another variable into the math. what about adding that $2-something bottle of octane booster? that might be cheaper than paying 20 cents more per gallon...

6/15/2008 5:41:24 PM

^^ & ^^^ Thank you both very much for your insight. I figured there were those kinds of safeguards in place but in the day & age of high gas prices and the gas stations getting squeezed for profits I just wonder what lengths they might go to in order to make that extra dollar.

6/15/2008 5:46:11 PM

Quote :

"let me throw another variable into the math. what about adding that $2-something bottle of octane booster? that might be cheaper than paying 20 cents more per gallon..."

doesn't do a fucking thing on a run of the mill car

6/15/2008 5:46:14 PM

^^^Only if it can boost from 87 octane to 93; I think it would only boost 15 gallons to 89 or 90, so probably no.

[Edited on June 15, 2008 at 5:52 PM. Reason : ^^]

6/15/2008 5:51:40 PM

yeah those gas mileage additives and octane boosters dont do shit...cnn did a report on this recently actually

6/15/2008 5:53:45 PM

yea they aren't worth it at all and do little to nothing

6/15/2008 6:12:54 PM

once again, i nominate shell vpower

6/15/2008 6:15:58 PM

Quote :

"let me throw another variable into the math. what about adding that $2-something bottle of octane booster? that might be cheaper than paying 20 cents more per gallon... "

This something I've read a bit about...

Back when I was stationed in FL, I drove a Honda S2000--the car has a stratospheric (for a production street car) 11.x:1 compression ratio, and on top of that, mine had a supercharger added (aftermarket) which breathed an extra 5.5-6 psi of boost. To spare you the mechanical engineer stuff and make a long story short, it was amazing to me that it ran on 93 octane fuel--there was no way in hell I would've tried any lesser grade in it.

Well, a hurricane came through, and fuel became all but completely unavailable for at least a week. Even after that when a few stations got a truckload in, it was always 87 octane for the next week or two. That did me approximately zero good.

I started researching online about octane booster additives. The vast majority of them are basically snake oil. They do increase octane ratings, but only by a tenth or two of a point per bottle (i.e., meaningless--you'd have to use like 2 dozen bottles). There are a couple of brands that actually do raise your fuel's octane rating by a meaningful amount, but these brands are expensive--far more expensive than just buying high octane fuel (especially now that the price of gas has risen a LOT, but the spread between grades is often still just 10 cents).

If this trend continues (ever more expensive gasoline with a pretty much constant price spread between grades--i.e., a therefore falling percentage difference), it may very well become more cost effective to start designing new vehicles with higher compression ratios and more aggressive ignition timing maps to take advantage of higher octane fuel (for efficiency reasons, not just performance. I don't know how hard it would be to convince the layman of this and market an economy car that requires 93 octane when gas is pushing $5/gallon, but I think it may be viable from a cold, hard numbers perspective.


One idea that I've heard is to stop using corn-based ethanol as an alternative fuel (as most of us know how dumb of an idea that is turning out to be), but to use it as an additive. Basically, even a car that requires high octane fuel only really requires it when the engine is under load, like accelerating. Ethanol is a pretty effective octane booster (I think that's what the additives in a bottle mostly are, actually). We could design cars to hold a reservoir of ethanol that would only be injected into the fuel-air mixture when needed. You'd have to refill this reservoir seperately from your gasoline, of course. It could be designed so that the car could drive without it, just with reduced performance. This could be incorporated with gasoline-electric hybrid designs, too, as these designs have the benefit of only operating the gas engine when under significant load (which can allow the gasoline engine--or a diesel engine--to be designed more efficiently.)


[Edited on June 15, 2008 at 6:31 PM. Reason : asfdads]

Quote :

" Thank you both very much for your insight. I figured there were those kinds of safeguards in place but in the day & age of high gas prices and the gas stations getting squeezed for profits I just wonder what lengths they might go to in order to make that extra dollar. "

This is something I don't know for sure, but I've heard that gas stations actually have pretty slim profit margins. They make some money on gas out of sheer volume, but the big deal for them is the stuff inside--especially tobacco and alcohol.

[Edited on June 15, 2008 at 6:33 PM. Reason : asdfads]

[Edited on June 15, 2008 at 6:33 PM. Reason : asdfasd]

[Edited on June 15, 2008 at 6:43 PM. Reason : asfdad]

6/15/2008 6:22:53 PM

You are correct, sir. I heard a figure one time. It might be pennies per gallon, but I think it is pennies per tank that they make in profit. Some full-service stations have had to stop selling gas alltogether because of the higher price they charge for the service and the amount that it has killed their profits.

6/15/2008 9:47:51 PM

I've accidentally put regular in my car once (realized it 1/2 way through the filling). Another time the jackass attendent (thank you NJ for no self serve) starting pumping me up with regular. After both instances I just took it easy on the car till I could get more high octane in there, i.e. no flooring it, high rpm shifts, etc.

6/15/2008 10:13:56 PM

My car is built for 91, and I usually use 89. However I tried the Premium vs. Plus experiments for a bit as well. Over a couple of months I measured (roughly):
89: 230 miles
93: 280 miles
93: 250 miles
93: 300 miles
93: 240 miles
89: 250 miles
89: 300 miles
89: 280 miles

It seemed to depend more on my driving habits...

The lesson I learned: I would really need a long term test of a few months for each octane where I didn't take any long-ish trips to determine if Premium gave me better mileage.

6/15/2008 10:33:33 PM

http://www.toptiergas.com/

BP does NOT make the cut

of course, that site is really plain jane so make your own opinions

6/16/2008 8:52:51 AM

for those who have to buy Premium, don't feel bad. Regular will be that price in a few weeks

6/16/2008 8:58:24 AM

i alwasy use 93 shell in the bike even though it only needs 87. But its so little difference in price in the small tank i dont care.

6/16/2008 10:21:44 AM

Quote :

"Ethanol is a pretty effective octane booster (I think that's what the additives in a bottle mostly are, actually). We could design cars to hold a reservoir of ethanol that would only be injected into the fuel-air mixture when needed. You'd have to refill this reservoir seperately from your gasoline, of course. "

VTEC Juice?

6/16/2008 10:24:30 AM

I always read this thread as "Gasoline Meth"

6/16/2008 10:27:46 AM

or Gasoline Myth

6/16/2008 10:37:32 AM

Quote :

"if your car does not need higher octane, you are wasting money by using it."

okay, i know people mentioned this before, but i really do disagree with you

my old '95 v6 mustang specifically said to use 87...when i had the car, i was driving roughly 2500 miles per month (really, my driving regimen at that time varied little, so i think it was a pretty well-controlled experiment)...so for two months, i kept explicit records on where i was driving and how far...the first month was my usual 87 and the second was 93...on 87, i was getting about 27-28mpg...with 93, though, i got 30-31mpg

i don't know how anyone can argue with this...the car ran just fine, as far as i could tell...i saw no change in "performance" either way, so i came to the conclusion that using premium was a better deal (at that time, premium was only $0.15/gallon more than regular where i was buying gas)

that said, i don't know much about cars in general, so maybe i'm missing something

i've wanted to try it out with my saturn, to see if it would matter, but the gas station i usually buy at has premium for $0.30/gallon more, and i just can't bring myself to try it

6/16/2008 12:17:08 PM

9.4:1 Compression on a Civic with 93 FTW?

Seriously though, theduke is right. If your engine isn't going to take advantage of the higher compression available due to the higher octane, there is absolutely no point in using the more expensive gas.

All 93 buys you is a higher compression ratio....for instance an S54 M3 is 11.5:1, it needs the 93 to achieve maximum compression.

6/16/2008 1:28:10 PM

^^how high was the mileage on your Mustang? As mileage increases your engine can form carbon deposits inside the combustion chambers which raise your compression ratio. Hot spots can also form. If this is the case then you'd definitely benefit from 93 octane.

6/16/2008 1:47:30 PM

more than likely, you're not driving the same way each time. There's a lot more variables involved. Someone call mythbusters and tell them to test this shit out.

6/16/2008 2:31:50 PM

Quote :

"Someone call mythbusters and tell them to test this shit out."

ha. if they test this as badly as they tested "windows open vs. AC" then I'm not too curious about the results

6/16/2008 4:11:25 PM

Quote :

"All 93 buys you is a higher compression ratio....for instance an S54 M3 is 11.5:1, it needs the 93 to achieve maximum compression. "

To be more correct, it buys you the ability to operate with a higher compression ratio, which determines your thermal efficiency (i.e., how much energy is extracted from a given amount of fuel). Therefore, that E46 M3 needs high octane fuel to not suffer from detonation or pre-ignition due to its high compression ratio.

All octane rating means is a measure of resistance to detonation. 87 octane fuel is more volatile than 93 octane fuel. Because of this, the 93 octane fuel-air mixture can be compressed more in the cylinders, which yields more power and efficiency.

6/16/2008 4:32:33 PM

ha. I saw that show and was like "oooh windows v AC". AC actually does work better for me. I've averaged a 2mpg increase on my trips between raleigh and wilmington when I use my ac on high instead of rolling down my windows. went from about 13.4 to 15.6 Also get better mileage with my tailgate up but it isn't as noticeable.

6/16/2008 4:36:18 PM

^^^^^ when i tested it, around 100k

^^^^ well, i'm sure it's not EXACTLY the same, but it was VERY close...it was a pretty regular schedule...the odds that that EXACT period of time was significantly different to account for the change in mileage is pretty low

meh...again, i don't know much about cars and such...i did my simple experiment and reached that conclusion (i used the same brand of fuel and oil, and maintained correct pressure in my tires, too)

[Edited on June 16, 2008 at 4:37 PM. Reason : arrows]

6/16/2008 4:36:39 PM

^not that I'm doubting your claim of relatively same situations, how did the weather vary? Humidity hurts mileage (in addition to extreme heat or cold).

6/16/2008 5:17:58 PM

Quote :

"for those who have to buy Premium, don't feel bad. Regular will be that price in a few weeks "

the original point of this thread was me coming to the realization that because my car is supposed to use premium and I haven't been buying premium, that I'm wasting money.

I also came to the realization that, for me and my car, even though the price per gallon for premium is more expensive, the price per mile significantly counteracts the price per gallon.

so in effect i've concluded and have stuck with the mindset that by buying premium, i'm buying cheaper equivalents of regular/plus gasoline and getting a whole lot more bang for my buck...

6/16/2008 5:30:05 PM