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Old 04-02-2007, 12:28 AM   #1
Kaotic Lazagna
 
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Premium Gas

okay, to make this short, i filled up with premium gas at Chevron, the only place i ever get gas...i drove on average of 70 mph...and i just filled up again and calculated my mpg...i got 39 mpg. ????? when i fill up with regular and drive at an average of 65 mph, i get 36-38 mpg.

but yeah, i'm not sticking with premium, just wanted to test it out.

can anyone tell my why i was able to get better gas mileage with premium? i didn't think it mattered which grade fuel??????
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Old 04-02-2007, 12:35 AM   #2
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someone at the dealership told my not to use 87, they told me rather use 89 or premium. I have no ideas, but i would like to know more about this too.
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Old 04-02-2007, 01:04 AM   #3
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Manual says regular (87 octane) gas, wallet says regular gas, car get regular gas...

-Peter
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Old 04-02-2007, 01:10 AM   #4
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Quote:
Originally Posted by daq421 View Post
Manual says regular (87 octane) gas, wallet says regular gas, car get regular gas...

-Peter
hahha same here, my wallet is not enough to fill Premium now a day, beside i filled one time and i heard more noise from the engine, dind't pay attention to MPG.
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Old 04-02-2007, 01:12 AM   #5
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I remember my Mini Cooper S only took premium. Isn't it called premium for a reason though? Makes sense to me you would get better mpg. I'd fill up with premium all the time if I had the ends.
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Old 04-02-2007, 01:18 AM   #6
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premium gas is typically used in order to prevent a symptom called engine knocking. Engine knock happens when you get preignition of the fuel / air mixture before the spark can light it and give you a clean burn at top dead center of the piston. Essentially the mixture is combusting too early. Higher octane fuel is more resistant to preignition from compression. Thats all. Generally high compression engines require higher octane fuel but thats changed dramatically based on really advanved engine management systems technology. It used to be that anything with more than 9:1 was running premium, but nowadays engines can run 11:1 on 87 octane. just check out some honda engines. How? Well I'm not sure but our Yaris is set up to run on 87 octane without knocking so thats what I use. The reason you can get more power by running 91+ octane is that the engine management computer probably just advances the timing to take advantage of the better fuel. Will it increase fuel economy? Perhaps a tiny bit but certainly not 20% more. There is absolutely no evidence that running higher octane fuel in an engine thats supposed to run on 87 will make any difference. Totally different story for the bigger and badder engines. Higher compression, longer stroke, high revving engines need it. the yaris...not so much. stick with the 87. if the prices in your area are similar to mine, you'll appreciate the savings!

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Old 04-02-2007, 01:34 AM   #7
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That's what I meant to say...errr
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Old 04-02-2007, 02:24 AM   #8
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It is not to prevent engine knock. Engine knock is from rods comming loose or lifters rattling,ect.

The real reason people use higher octane fuel is to prevent a thing called "Predetonation"...I made a whole post on this in another thread on this same forum.

QUOTE:

High octane rating only determines at what point the fuel will combust. A high octane fuel is to prevent a thing called "Predetonation" from occurring.
Predetonation is not a term you ussually hear in parking lots full of kids showing off their cars, ussually it is used at the dragstrip listening to guys talk about their 400+HP 4cyl boosted cars.

Predetonation is what happens when due to pressure in the combustion chamber the fuel ignites prematurely before the spark plug triggers. This is a very bad thing, because if the number 1 cyl predetonates, it goes against the crankshaft being turned by the pistons that are firing in the correct order with their spark plugs.

The force inside a cylinder chamber becomes increasingly higher when you try to force 20 PSI of boost into it. When the piston goes on what is called the compression stroke(the stroke where it mashes the mixture of air and gasoline together in preporation to be ignited) the pressure can sometimes be enough to cause the mixture to explode.

High octane rated fuel is used to prevent the gasoline and air mixture from blowing up before it is supposed to. The only benifit to using high octane fuel on a car that was designed for 87 octane piss water is that it sometimes burns cleaner because some gas stations may put more adatives in it and sometimes it is a slightly better grade of fuel.

If you ever get boosted or change the compression to something radical(say 14 to 1) then look into 89 octane, untill then, feel free to waste your cash on the gas that costs 30 cents more a gallon.

END QUOTE



P.S. You do NOT get more power from running higher octane fuel unless you are running insane compression or boost. It does not burn cleaner, it does not burn hotter. The only thing high octane fuel is cause it to combust later than a lower octane fuel would. Your computer will neither advance NOR retard the timing just by going up 2 points in octane. Better gas mialge is completely coincedental, and is not scientificaly probable.

The only thing high octane fuel in your little 106hp gas miser engine will do is drain your pockets of the excess money you seem to possess. Be prepared for extra fuel injection services...because the delayed ignition doesnt allow for as clean of burn, so your engine will get covered with carbon deposits on the valvetrain.

P.S.P.S. If you dont belive me look on the internet, or look in a issue of sport compact car, they already debunked the whole "octane=hp" bullcrap.
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Old 04-02-2007, 03:00 AM   #9
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[QUOTE=Kaotic Lazagna]

can anyone tell my why i was able to get better gas mileage with premium?QUOTE]

This post has gotten

I think your mpg fluctuated because of other factors. A change in temp could cause the tire pressure to change by 10% resulting in better/worse mpg. Maybe you did more city driving? More passengers = more weight, less mpg...

Bottom line, you experianced higher mpg on this tank of gas which could be indepandant of the octane rating. mpg is affected by so many factors, you may never know excatly why that tank was slightly better.

back off topic, engine knock and predetonation are two terms for the same thing...

Last edited by fu_im_from_texas; 04-02-2007 at 03:31 AM. Reason: fix quote
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Old 04-02-2007, 03:07 AM   #10
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[QUOTE=fu_im_from_texas;69779]
Quote:
Originally Posted by Kaotic Lazagna View Post

can anyone tell my why i was able to get better gas mileage with premium?QUOTE]

This post has gotten

I think your mpg fluctuated because of other factors. A change in temp could cause the tire pressure to change by 10% resulting in better/worse mpg. Maybe you did more city driving? More passengers = more weight, less mpg...

Bottom line, you experianced higher mpg on this tank of gas which could be indepandant of the octane rating. mpg is affected by so many factors, you may never know excatly why that tank was slightly better.

back off topic, engine knock and predetonation are two terms for the same thing...
not sure why either. my factors remaind the same, for the most part. the only difference is that i was driving faster and the gas itself. but i'm not willing to get another tank of premium to find out. lol...
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Old 04-02-2007, 03:31 AM   #11
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Question donno?

Quote:
Originally Posted by Kaotic Lazagna

not sure why either. my factors remaind the same, for the most part. the only difference is that i was driving faster and the gas itself. but i'm not willing to get another tank of premium to find out. lol...
one of my best tanks was 42.xx mpg...from el paso to dfw...700 miles of +80 mph...
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Old 04-02-2007, 04:13 AM   #12
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[QUOTE=fu_im_from_texas;69779]
Quote:
Originally Posted by Kaotic Lazagna

can anyone tell my why i was able to get better gas mileage with premium?QUOTE]

This post has gotten

I think your mpg fluctuated because of other factors. A change in temp could cause the tire pressure to change by 10% resulting in better/worse mpg. Maybe you did more city driving? More passengers = more weight, less mpg...

Bottom line, you experianced higher mpg on this tank of gas which could be indepandant of the octane rating. mpg is affected by so many factors, you may never know excatly why that tank was slightly better.

back off topic, engine knock and predetonation are two terms for the same thing...

It is on topic...explaining how octane works answers the question. Your better MPG was a result of another factor and is completely seperate from fuels octane.

P.S. the actual term for Predetonation is called "Pinging"...not knocking...a knock normally refers to a rod or valvetrain noise...course...predetonation, bad lifter, rod knock, piston slap...all the same thing, right?
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Old 04-02-2007, 07:01 AM   #13
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89 octane was tested to get the higher mpg rating posted on the window sticker of our car
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Old 04-02-2007, 10:57 AM   #14
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Use reg and its cheap
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Old 04-02-2007, 11:13 AM   #15
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[QUOTE=Spades;69789]
Quote:
Originally Posted by fu_im_from_texas View Post


P.S. the actual term for Predetonation is called "Pinging"...not knocking...a knock normally refers to a rod or valvetrain noise...course...predetonation, bad lifter, rod knock, piston slap...all the same thing, right?
ooops! i meant engine pinging, you are correct! but many use the terms ping and knock interchangeably. either way, higher octane prevents preignition or predetonation, as we stated, and shouldnt be used in our yarii. kaotic's higher mpg may have been cause by better drafting behind cars, a stronger tailwind, who knows! but it definitely wasnt the use of higher octane gas...and i agree that this is definitely ON TOPIC! now, if i started talking about how kaotic's choice of laundry detergent affected his mpg, that would be considered off topic...

--B
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Old 04-02-2007, 11:17 AM   #16
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Screw all of you, I'm going to make the 20 minute drive up to Ravenna and grab some 105 octane. I'll let you know what happens.
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Old 04-02-2007, 11:20 AM   #17
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Quote:
Originally Posted by Black Yaris View Post
89 octane was tested to get the higher mpg rating posted on the window sticker of our car
Where did you read that??
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Old 04-02-2007, 11:30 AM   #18
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[QUOTE=static808;69893]
Quote:
Originally Posted by Spades View Post

ooops! i meant engine pinging, you are correct! but many use the terms ping and knock interchangeably. either way, higher octane prevents preignition or predetonation, as we stated, and shouldnt be used in our yarii. kaotic's higher mpg may have been cause by better drafting behind cars, a stronger tailwind, who knows! but it definitely wasnt the use of higher octane gas...and i agree that this is definitely ON TOPIC! now, if i started talking about how kaotic's choice of laundry detergent affected his mpg, that would be considered off topic...

--B
lol...i use Tide for the most part. that was when i was gettin 36-38 mpg. then i switched to All, and i got 39 mpg. really tho...this happened...but there better be no connection or else imma go crazy!
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