How much can a tank of gas affect performance??

ShadowHunter

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Aug 27, 2001
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I filled my little Eclipse with 87 octance as usual today. As I was pulling away from the gas station, she seemed a little peppier then usual, so I floored it when I was in the clear. She fvcking took off!! I've never had that car perform so well. Did the gas station mix octanes, and higher octane makes better performance? Some additive?? What could possibly transform my car like that??
 

Kenazo

Lifer
Sep 15, 2000
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a tank of gas can have huge results on your performance. IE: no gas in tank = very poor performance :)
 

ShadowHunter

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Aug 27, 2001
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<< IE: no gas in tank = very poor performance >>



BIG DUH there.

Anybody else got a serious answer for me?? I'm genuinely curious here...
 

BCYL

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Jun 7, 2000
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It really depends on what kind of car and what kind of condition it is in...

I remember a magazine did a test with a BMW, dynoing it with different octane gas, it made absolutely no performance difference...

However, some cars that requires a certain grade of fuel are known to change the timing if a lesser grade is put in, which would decrease it's performance....

 

Brutuskend

Lifer
Apr 2, 2001
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Higher Octane can def. increase performance!

I know you said your using the same Octane as usual, but it's not unknown for stations to NOT pump the gas you think your getting.

Maybe this time it WAS 87 Octane!

From time to time I stick booster in mine, and I do notice an improvment.
 

Kenazo

Lifer
Sep 15, 2000
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on a serious note. It is not really possible for so big a change to occur as soon as you started your car. unless your gastank was completely empty before you filled her up, the mix will not be that noticable. Also, the octane level really does nothing for performance unless the engine is designed for it. The benefit of 92 octane is that it ignites at higher temps, thus allowing greater compression. as for additives; where did you fill up? different companies use different additives.
 

ShadowHunter

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Aug 27, 2001
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<< on a serious note. It is not really possible for so big a change to occur as soon as you started your car. unless your gastank was completely empty before you filled her up, the mix will not be that noticable. Also, the octane level really does nothing for performance unless the engine is designed for it. The benefit of 92 octane is that it ignites at higher temps, thus allowing greater compression. as for additives; where did you fill up? different companies use different additives. >>



I was very very empty. And it did idle for a minute while I put away the receipt and crap. I filled up at the place I always do, a Shell around the corner.
 

thomsbrain

Lifer
Dec 4, 2001
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if it has fuel injection, the new gas should hit pretty quick...

edit: it probably had to do with dirty fuel injectors that got jarred/flushed clean.
 

Brutuskend

Lifer
Apr 2, 2001
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Fuel will seperate as well.

My car run's MUCH better when it's low on gas.

Part of that is it's weight when low on fuel, but part of that is that it seems the fuel that rise's to the top (and is burned last) tends to be higher Octane.
 

Kenazo

Lifer
Sep 15, 2000
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I'd be willing to bet on some junk being knocked outa the fuel injectors. Other than that, i can't see any reason for a change. Octane doesn't change performance unless it is in a car designed to be run w/ a higher compression ratio.
 

audiophan

Senior member
May 2, 2001
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if you ran your tank low, the the sludge on the bottom of your gas tank most likely would have been sucked into your injectors
they get dirty
this is bad

higher octane gas will have more of a performance increase in high compression engines than in low compression naturally aspirated bmw's
turbo in an eclipse makes it a high compression engine
this is good


this is what i gather from reading to many motor trends' and other car mag's
 

Brutuskend

Lifer
Apr 2, 2001
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Thats true for the most part, but there are exceptions.

It's a older car, carbon sometimes builds up on the tops of pistons & heads increasing the comp. ratio.

If he drives in town a lot, it's more likely to build up carbon. In a case like that Octane COULD make a differance.
 

Looney

Lifer
Jun 13, 2000
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Out of curiosity, does anybody know if my car would run better on low or high octane fuel? It's a 98 Mustang.

As for as gas, i use lower octane. I don't notice a difference between higher and lower myself.
 

Alienwho

Diamond Member
Apr 22, 2001
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I *heard* that when you run your car on empty for a while it is possible for water to condense and mix with the gas in the tank, thus giving you crappy performance, but when you fill it up it the water neutralizes more or less, thus increasing performance.
 

Tominator

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Oct 9, 1999
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<< Higher Octane can def. increase performance! >>



If that is the only variable, that is a patently false statement.

ShadowHunter either had a 'heavy foot' after the fillup or something was amiss in the engine. It had ZERO to do with the gas if the remaining gas in the tank wasn't polluted with water or impuritys that might have been impeding proper running.

There are very few differences in gas regardless of the brand. They meet a particular standard and ANY ingredient added is controlled by the Government. There are no secrets in gasoline formulation.


To simplify it, the octane rating's only effect is in it's resistance to detonation. Detonation,or pre-ignition as it is sometimes called, occurs when the fuel-air mixture in the cylinder 'explodes' instead of burns. The pressure increase in the cylinder caused by higher compression by design or carbon buildup possibly,cause the mixture to ignite before it is supposed to. Advanceing the timing too far has the same effect. You can heardetonation. It sound like someone rattleing marbles around in a coffee can when the car accelerates.

If there is no detonation and the car is in tune you are wasteing your mone on a higher octane blend.

In gasoline engines the mixture must burn at a controled rate. In diesel engines the fuel explodes by design. That is why you hear that signature rattle of a diesel.
 

Zenmervolt

Elite member
Oct 22, 2000
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<< Thats true for the most part, but there are exceptions.

It's a older car, carbon sometimes builds up on the tops of pistons & heads increasing the comp. ratio.

If he drives in town a lot, it's more likely to build up carbon. In a case like that Octane COULD make a differance.
>>

The ONLY reason that higher grade gas would help unclog things is that generally more detergents are added to the higher octane fuel. The octane rating (more accurately called the "anti-knock index") has nothing to do with performance unless your car requires it. If the car ran without spark knock when running on low octane fuel and the engine is not designed for high octane, then running premium fuel has no effect on anything other than your wallet.

ZV

EDIT: Tominator; Thank you very much, I hadn't ever given a thought to why a Diesel engine sounded that way. I should have noticed that it sounded just like detonation.