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04-02-2007, 12:28 AM | #1 |
Drives: '14 GT86, '08 Vitz Join Date: Dec 2006
Location: Central Valley, CA
Posts: 9,873
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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?????? |
04-02-2007, 12:35 AM | #2 |
The Beautification of Car
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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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04-02-2007, 01:04 AM | #3 |
MPG is the new cool
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Manual says regular (87 octane) gas, wallet says regular gas, car get regular gas...
-Peter
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04-02-2007, 01:10 AM | #4 |
The Beautification of Car
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04-02-2007, 01:18 AM | #5 |
Engineer/Artist/House-Dad
Drives: 2006 Toyota Sienna XLE Join Date: Aug 2006
Location: California
Posts: 419
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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!
--B
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04-02-2007, 01:12 AM | #6 |
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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04-02-2007, 01:34 AM | #7 |
That's what I meant to say...errr
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04-02-2007, 02:24 AM | #8 |
The Hated One
Drives: 07 White Manual Sedan Join Date: Sep 2006
Location: Oregon,USA
Posts: 390
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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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04-02-2007, 03:00 AM | #9 |
[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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04-02-2007, 03:07 AM | #10 | |
Drives: '14 GT86, '08 Vitz Join Date: Dec 2006
Location: Central Valley, CA
Posts: 9,873
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[QUOTE=fu_im_from_texas;69779]
Quote:
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04-02-2007, 03:31 AM | #11 | |
donno?
Quote:
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04-04-2007, 09:51 AM | #12 |
Drives: 2007 Yaris Liftback Join Date: Sep 2006
Location: Chicago
Posts: 129
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04-04-2007, 12:39 PM | #13 |
Drives: '14 GT86, '08 Vitz Join Date: Dec 2006
Location: Central Valley, CA
Posts: 9,873
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06-22-2007, 04:44 PM | #14 | |
Mr Attitude
Drives: Blazing Blue 5 Spd Join Date: Jun 2007
Location: Hillsboro
Posts: 302
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[QUOTE=Kaotic Lazagna;69781]
Quote:
If you get 10% better gas mileage with premium, as some have stated (36mpg with regular, 40mpg with premium, etc), then you will be driving as far on 10 gallons or premium as you would be on 11 gallons of regular... Stop me if I'm losing anyone... Gas is now above $3 a gallon around my area. You are saving .80 cents if you see 10% better mileage with premium... I'm thinking this is along the lines of the placebo effect, you believe your more expensive purchase is going to help you, so it does... Also, how much do you all drive if an extra $2.20 a tank for premium is breaking your wallet? If you drive 10,000 miles a year at 40 mpg, that is about 23 fillups. That is $50 a YEAR... Sorry for the ramble...but if you believe that premium is helping you, buy it. Scientifically, there is no benefit to running premium in these cars... |
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06-22-2007, 06:37 PM | #15 |
Clean and (dis)Functional
Drives: Yaris 2dr--Black Betty Join Date: Mar 2007
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[QUOTE=jdium;101220]Don't understand how you can say that! Scientifically, under load the higher octane allows more timing advance before knock (in a 10.5:1 compression ratio car) which is more efficient, using less fuel for the power needed....not under load I agree with you.
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06-23-2007, 04:06 AM | #16 | |
Mr Attitude
Drives: Blazing Blue 5 Spd Join Date: Jun 2007
Location: Hillsboro
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[QUOTE=churp;101248]
Quote:
If what you say is true, why don't the Toyota engineers tell us to use premium? |
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04-02-2007, 04:13 AM | #17 | |
The Hated One
Drives: 07 White Manual Sedan Join Date: Sep 2006
Location: Oregon,USA
Posts: 390
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[QUOTE=fu_im_from_texas;69779]
Quote:
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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04-02-2007, 11:13 AM | #18 | |
Engineer/Artist/House-Dad
Drives: 2006 Toyota Sienna XLE Join Date: Aug 2006
Location: California
Posts: 419
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[QUOTE=Spades;69789]
Quote:
--B
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