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Discussion Starter #1
Hoping somebody has some data to back this up...

The Car: 2004 Focus SE, 5-Spd, 2.0L Zetec, Bone-Stock

The Question: I am noticing that I get about 2 more MPG out of the car when I run premium gas (93-octane) vs. regular gas (87-octane). The only way that could happen (if it is really happening) is if the knock sensor and ECU system are allowing more ignition timing with the 93-octane than with the 87-octane, particularly at low revs (say 1,500 to 2,500 RPM). I'm not talking about WOT, I'm talking just part-throttle acceleration from a stop sign.

Has anybody else noticed this? Has anybody been able to measure the ignition timing difference with different fuels?

Thanks,

Mike
 

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FoFo Lover.
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I have no hard evidence...but I've noticed the same thing.....Higher Octane better the Gas Mileage...

i just can't justify the 2-3 more MPG and spend $.30 more per gallon. lol
 

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Machinery Technician
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i make exactly the same 24MPG wether i run 87oct or 93 oct [dunno]
 

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Machinery Technician
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i've tried a couple times with the same effect. i used to always run 93oct, until gas got ridiculous. then started using 87oct and really, my car runs the same. it's made to run on 87oct anyways.
i might have to try driving more calmly for a tank and see if that helps.
 

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MyCarBreaksAlot
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You will have to do a lot more testing. That 2 mpg could have easily been from driving in a tail wind vs a head wind. There's just so many variables.

I do know however that when I run around with my hot air intake in the summer, the car bogs to no end and I get terrible mileage due to timing adjustments. I imagine that really wouldn't come in to play up where you are though, we're talking like 100 degrees ambient air.
 

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Machinery Technician
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I do know however that when I run around with my hot air intake in the summer, the car bogs to no end and I get terrible mileage due to timing adjustments. I imagine that really wouldn't come in to play up where you are though, we're talking like 100 degrees ambient air.
hmmm, i hadn't thought of that. maybe i'll get better mpg when i install the homemade cai I'm setting up. i do get a lot of bogging from heat soak with my short ram
 

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Do all the testing you want, but the car will be more efficient with 93 when compaired to 87.
 

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Yes on a zetec as well.

even thougth the Zetec is an 87 octane car the ECU will take advantage of 93, there are these things in the tune called adders... and as long as the ECU doesnt see any knock they will add timing (up to a preset amount) which will both increase power and give you a better more complete combustion.
 

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Machinery Technician
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cool thanks.. So maybe I get the same MPG, but make a little bit more power with 93oct.
 

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So, I just did some basic math. And if the MPG improvement stays consistent ... driving 1000 miles a month, there would be some annual savings going on.

I did round to whole numbers, but that's not that big of a deal really. Talking pennies difference.

12000 miles
27mpg
445 gallons
$3.50/gal regular
$1555 total

12000
30mpg
400 gallons
$3.70/gal premium
$1480 total

75 bux may not seem like a lot ... but that's out and out savings. Since its not costing you anything to run the premium gasoline, other than the added cost per gallon when you tank up, but the increase MPG reflects in over all reduced costs per mile.
 

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As you put more miles on the engine, you'll get more carbon buildup; resulting in a higher compression ratio.

With a higher compression ratio, you'll need slightly higher octane, (the knock sensor will back off the advance with the 87, giving you lower mpg with the 87)
 

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i get much better mpg with 93 oct. i can go much further on a tank of gas with it and my car runs so much smoother
 

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le kittens meow
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running higher octane isent good for your car. You can read it everywhere, not all of it burns when it gets into the chamber therefore your waisting alot of it. Im sure i can find an article about it...hopefully its alright for me to post external links here..

its the 5th and 6th questions
http://myfordfocus.com/faq/
 
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