gas expiriment in the name of better MPG

[ooberdoob]

so my bud rodney always runs 89 in his 96 escort 1.9L. i inquired about it and he swears her gets better MPG and it outweighs the 10c difference. well the bastard goes forever on a tank. in teh 400mi area and his tank is smaller than mine.

so i bit, last night i had drained the car as low as i cared to go, (14.6 gallons to fill up) and filled it with 89.

here's how the gas normally works:
in ideal conditions, like cruise at 70-75 interstate, its 100mi first quarter, 200 by half, 350 with gaslight on, its time to get gas, and i'm still safe to miss a few exits. i ran 364 once and the needle was on the pin. never again.

went driving randomly with my friend jeremy

we went a few miles on a nice road, 60mph or so, and headed on to the forest service roads. second or third gear on gravel roads across mountains for..... well a couple hours or so, took the long way home, hour and a half more on the interstate...






120mi on the first 1/4.

on the 29mpg tank i wasn't that far over 100 yet; that was insterstate!



remember, the car's rated for 28mpg i think. please correct me if otherwise.

EDIT 27mpg highway as per cars101




i'll keep everyone posted, this seems like it'll have very nice results.

[badbasser98]

i've heard this from a few people, but never have seen any proof that higher octaine rating will yield better MPG. Please keep us posted on your results :wink: .... But then again you have to bring into question,(assuming you are doing this to save money) the extra money you spend to buy high octaine fuel, is that higher than what you would spend to just buy more lower octaine gas. Are you really getting anywhere?

-BB98

[Wiscon_Mark]

I've bought 89 before and it helped mileage a little (but there are so many other variables) but I don't know if it was worth it....

On turbo cars it will, because the fuel needs to be more refined because of so much more air going into it (also depends on compression) but if your car isn't engineered to do anything different than regular 87 octane, then it probably wont' make much difference.

One other thing to bring to mind....the oil companys could be cheating and making 87 more like 85 or something, and you're noticing the difference when you go up to what you're supposed to be at...I wouldn't put it past them to cheat here and there... :roll:

[ooberdoob]

well the main point is "is the difference worth it?"

i'll do my best to compare numbers cost wise when i'm done, but i think i'll need a math person's help.

the higher the price of gas goes the more economical it will be as the price diference is X+10c, not X*1.p: when X is the price of 87, and p is a percent higher.

in other words its not scaled, so at a dollar a gallon, 89 is 10% more, at $2, its only 5% higher.




thats the sharp limit of my math, and its prolly wrong.

[Wiscon_Mark]

actually, you're pretty much right...89 octane is usually only 5 cents more expensive than 87, no matter the prices....

[galek_98gt]

i always put 93.

[shazapple]

87 for me. Thats what the owners manual states, and I trust Subaru to know more about the engine than my butt dyno.

Ive filled up with 91 for a few weeks. I found that my car was slower and got less MPG.

[Wiscon_Mark]

I put in 89 just to see...

Its about 5* outside right now, its been bitter cold the last 2 weeks, and i've been getting terrible (read: 21mpg :shock:) mileage, and 89 was only 4 cents more expensive than 87, so I went for it.

[gil_ong81]

I’ve kept a log for the past few months.


Date______Miles____Fill____MPG
05/07/05___160____9.14___17.51
05/15/05___192____9.86___19.47
05/22/05___162____7.80___20.77
05/25/05___275___10.80___25.46___Highway
06/03/05___228___11.00___20.73
06/10/05___223___10.97___20.33
07/07/05___280___10.71___26.14___Highway
07/16/05___200___12.05___16.60___Parking Lot Survey
07/31/05___291___13.34___21.81
08/13/05___260___13.08___19.88
08/20/05___178____8.28___21.50___Some Highway
09/01/05___219___11.04___19.84
09/12/05___249___11.63___21.41___Some Highway
09/26/05___236___12.00___19.67
10/02/05___214___10.48___20.42___Fixed plug wire
10/16/05___210___11.44___18.36___Parking lot surveys
10/23/05___230___11.73___19.61
10/28/05___58_____4.07___14.47
10/30/05___219____8.12___26.98___Mostly Highway
11/03/05___135____5.84___23.06___93 Octane + Sea Foam + ran hard to clear up buildup
11/12/05___200___10.08___19.87___Back to 87 octane.
11/21/05___106____6.55___16.12


As you can see, i get about 26mpg on highway. and with 93 octane, it did bump mileage up almost 3 mpg even though i ran it harder than normal.

how do ya like THEM apples?! :D



disclaimer: results not definitive.

[Huffer]

I ran 89 octane from Speedway.
Last summer, I switched to 87 (also Speedway), and found no ill effects, regarding loss of MPG, or power.

I fill up at the same station 8/10 times.

[gil_ong81]

i had a tread on NASIOC a while ago asking some questions pertaining to octane ratings.

http://forums.nasioc.com/forums/showthr ... ght=octane (http://forums.nasioc.com/forums/showthread.php?t=743132&highlight=octane)

[Wiscon_Mark]

It really all depends on if you're pinging or not...

I guess I'll go back to 87, but i figured I'd try 89 since it was only 4Cents more expensive...

[RABID_SUB]

Strange. In Kansas 89 octane is cheaper than 87. 89 has Ethenol in it, witch is corn, witch KS is full of. I avrage 28 mpg :P

[shazapple]

Would a change to a lighter oil help fuel milage?

[Wiscon_Mark]

Would a change to a lighter oil help fuel milage?

Every little bit counts. But I doubt you'd notice it just by changing differential and tranny fluids.

[ooberdoob]

who the hell put race gas in my poll?!

[jey]

I put in 89 but I have a turbo on my car :)

[BAC5.2]

My Legacy gets 16mpg. I run between 93 and 100 octane all the time.

Forester gets 21mpg with a check engine light and 87 octane winter gas.

[NewGenSTi]

Ok, Octane in fuel basicly makes it harder to burn. The higher octane the harder it is to ignite the fuel. so you only want to put in the recomended octane to get the best burning mixture. The reason for high octane is in high performance High compression, turbo, or suparcharged cars. I used to have an ATV that I built up for racing with a 13:1 piston and smaller gaskets all that good stuff. running somewhere around 13.5:1 when all was said and done and I had to run 110 octane in it. because it would detonate the fuel before it sparked from all the compression if I didnt.
My STi required nothing less than 93 because when that turbo spools in a sense you are raising the compression thus causing detonation. Octane does not add performance at all. just makes the fuel harder to burn. so in any case the lower octane you can use the better fuel mileage you will get because you will get a cleaner fuller burn. More power, and less unburnt gas going out the exhaust pipe.

If you really want to improve your fuel mileage keep your oil changed, good plugs and wires, and check out your 02 sensors. they may not be bad, but if they are old they wont give as good of a reading. may still be within specs, but the computer will still be dumping a little extra fuel in to compensate.

And actually a bad 02 sensor could be the culprite for seeing a gain in MPG with higher octane. when more unburnt fuel is being poured down the exhaust it can trick the ecu into thinking that it is running rich, causing it to send less fuel into the combustion chamber. leaning it out a little bit making you get a few extra mpg.. this is just a thought though I have nothing to back this theory up. The octane however is a fact that you should only run the minumum needed

[Wiscon_Mark]

who the hell put race gas in my poll?!

oh, hehe :D

[ooberdoob]

oh, i guess i should finalize my thread...

no difference other than more money spent.

stick to what your car calls for.

note: my first car said 89 and i always used 87 and it was fine.

[LeeLee D]

I put 94 in, I could prolly go less though

[blackgtbeauty]

from what i understand all the higher octane does is prevent detonation in cars with tighter tolerances like the k20's in honda's and STi's, more tuned vehicles. I personally don't think it does crap for mileage.

just my $.02.

[Juggernaut929]

hello everyone,

i got a 91 legacy turbo sport sedan AT (ej22t), all stock, ive been experimenting with this a bit too,

inside the gas cap and in the manual it recomends to use premium fuel, this by me is 91 or 93, my mechanic said the car would do fine with 87 unless i get a knocking, i trust him, he specializes in subies, and he drives the same car too.

theres a flat strip of rt 3 that i tested it on, about 50 miles long, at my starting point theres a mobil that i filled on my usual 91 octaine with, drove the 50 miles and back, stayed at constant RPM and speed the whole way. (asside from getting off the exit, and turning around) also i had just replaced my engine and trans fluid and my tires were at full pressure(all 38psi), and air filter was new

i dont remember what my milage was and how much gas i burned or what it cost, but when i got back i topped off the tank and did the math, i got 25mpg, which was like 8c a mile at the time,

i did the exact same test 2 days later with 87 octaine, and i got 22mpg, for the cost difference i didnt notice anything realy, maybe a cent off or so per mile,

for me ill use the premium, like the dude above i trust subaru, they want theyre cars lasting as long as posible, my mech said i prolly didnt need the 91 unless it knocked, lucky for me my engine is still pritty tight and has no irregular sounds of any kind but ive herd alot of old subies having engine knock and needing highter octaine, my mom had a old 88 subaru GL wagon 5spd, and she needed 89 because of a knock problem

*gasp*
In conclusion: id say it doesnt do to much differnce, the cost outweighs the increase efficency id say pritty evenly, although i have herd that higher octaine fuel is better for turbocharged engines lik mine, i did this because i wanted to max out the efficency of my subie, turbo charged all wheel drive sedans arnt known for their fuel effiency, but the deciding factor for me would be that my engine sounds a world of difference better and my throttle response, hp and acceleration were all much better with the higher octaine fuel, thats why i go with the 91 or 93, or at the very least 89.

[MoclovFlop]

I use 85, but that's because I live 6000 feet above sea level. Less oxygen=less octane needed...er sumtin'

Colorado octane at most pumps -85, 87, 91

[gil_ong81]

i've been getting absolute crap mileage the past 2 weeks cos of the shitty weather. the past 3 days have been even worse. seems like a direct relation between the temperature and mileage.

[Plays_with_Toys]

I use 85, but that's because I live 6000 feet above sea level. Less oxygen=less octane needed...er sumtin'

Colorado octane at most pumps -85, 87, 91

I'll be trying out E40 this weekend. 4 gallons of e85 and the rest normal 87 octane. :twisted:

[Wiscon_Mark]

from what i understand all the higher octane does is prevent detonation in cars with tighter tolerances like the k20's in honda's and STi's, more tuned vehicles. I personally don't think it does crap for mileage.

just my $.02.

You will get better milage if your car can utilize the fuel - ie: a high compression vehicle.

For instance: the 3.2L V6 in the Acura TL has a very high CR, makes 268 HP and gets 33mpg highway. But it requires premium ;)

[yotabeater]

hey juggernaut:

it makes a difference in your car to run premium simply for the fact that it's a turbo model. turbo'ed cars almost always require higher octane gas to run efficiently. i had a talon tsi turbo awd, and if i didn't run premium gas in her, she would knock pretty bad under boost/moderate acceleration (i know this because i had a pocketlogger and could monitor all the engine's functions in real time, such as knock, timing, intake temp, etc), but then again, i was running a LOT of aftermarket shit on that ride. 8.5:1 pistons, cams, bigger turbo/fuel system, 3" exhaust, etc. etc.

[sansMYSTi]

Run the octane of gas that your car is tuned to run on - in most cases running more or less octane is not going to be of a benefit (cost or power).

Humans are "tuned" to breathe on our nitrogen dominant atmosphere - we CAN breathe on pure oxygen, but unless you are suffering some resipartory ailment, the extra cost of pure oxygen is not necessary nor cost-effective. A bit of an awkward simile, but there you go :wink: .

[Juggernaut929]

hey yotabeater

yeah thats why i usualy run 89 or 91, but i can say i do like using the better gas, it makes my engine sound an run so much better, mine is still all stock, i think the turbo is 8.7psi, and im pritty certain the heads are better than the NA it would make sense, when i tried to run regular in my subaru it felt so crappy. it had a slight knocking that i could hear under hard acceleration, and at one point i couldnt get the engine to start, but idk if that was the problem, a month later my fuel pump went bad, so i think that coulda been the problem

i hate to think if the two previous owners always put in 87, im not sure if they did, but they could have, from what i gathered they were both middle aged women, who smoke, and put a couple nice dents around the car, and a couple nice big bumps on the bumpers, thank god for oldschool steal bumpers that actualy stick out from the car.

a kid in my apartment building is racing out a TSI, its pritty nice, he sets off car alarms everywhere with his 4in exhaust


To sansMYSTi good analogy


again im resting that ill stick with the good fuel, if it doesnt make much differnce for cost, why not treat your engine right

[Khanhfucious]

I cant ever break 21MPG. :-?

Same results with 93 and 89.

[sansMYSTi]

I generally hit about 23 MPG running on 87, though not lately while running on winters.