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Discussion Starter · #1 ·
In the area I live in (MD), gas comes in 87, 89, and 93 octane. I was talking with a friend of mine about the octane writeup and we got talking about what each of has to use for our vehicles (he only needs 87, I need at least 91 on mine). He said that he used to fill 89 octane but was frustrated by the huge price gap between it and 87. So he would fill up around 2/3s of his tank with 87, then do the last 1/3 with 93 since that would effectively make "89" octane, but cost considerably less. The thinking goes like this... 87 octane is equal to $n/gal, 89 octane is equal to $n+0.20/gal, and 93 octane gas is equal to $n+0.30/gal. So, instead of filling say 15 gal of 89 octane (=$n+3.00), he fills up 10 gal of 87 octane ($n) and 5 gal of 93 octane (=$n+1.50) which effectively saves him $1.50 each fillup. Sounds kind of funny doesn't it? I do admit that I've now noticed that many stations have a disproportionate price increase between 87 and 89 fuels, but not as bad with 89 and 93. In theory, this should be correct, but in practice, I'm not so sure. I suppose it is a cheaper way to get effectively 89 octane fuel, but I've never had to worry about it. However, with a truck like the Tundra, those that want slightly higher octane may be able to do that using this method because a truck will benefit most from this apparent "loophole" since the gas tank is large and the effort is more worth doing (i.e. at 24 gals, the savings will be $2.40 each time), though personally the difference isn't enough for me to make the effort if I needed to... what do you think? :D
 

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Yeah....I'm not going to put that much thought into a simple task. I get to the pump and get either 89 or 91 and fill it up. I'm not sure why I alternate between the two.
 

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I thought the owner's manual only called for 87 octane?? :confused:
 

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Jedi Ninja in Training
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That means you fill it with 87.
I have been running 87 with no ill effects.
I will be running several tanks of 91 to see if there is a mileage improvement, if there is, I will definatley be doing the math.
 

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I live in an area of Texas (Amarillo) that not only has the highest gas prices in the entire state; but the lowest octane, or regular unleaded, is only 86 octane. Figure that in and we're getting hosed.
 

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Wasting your money by putting anything other than 87 in anyway. It calls for 87, it runs on 87, buy 87. It won't run better, or get better MPG by running anything other than 87.
Problem solved.
 

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Jedi Ninja in Training
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Wasting your money by putting anything other than 87 in anyway. It calls for 87, it runs on 87, buy 87. It won't run better, or get better MPG by running anything other than 87.
Problem solved.
I call B.S.

I have proved it to myself time and time again. So unless the 5.7 motor is drastically different than any other internal combustion motor, I think higher octane will improve the mileage. If I am wrong, I only wasted around $20 bucks over 4 tanks of gas.
 

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87 for me
 

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If it calls for 87, I'd probably be using 89+ at sea level. Up here, I'll stick with 87, the small loss of compression due to thinner air and slightly lower air pressure justifies it. 87 is mid-grade here in CO for the same reasons..:tu:
 

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Discussion Starter · #13 ·
My understanding is that higher octane = more power. That may not necessarily translate into better mileage but in theory, more power means your vehicle doesn't have to work as hard to do the same speed. Also, higher octane helps avoid engine knock for anybody that is concerned about it.
My personal experience, my car has a larger engine, weighs 200lbs more (plus 80lbs more than that if you consider the weight of the driver :D ) than my wife's car and I still get better gas mileage (she gets around 22.5mpg, I get about 25.5mpg). She uses 87 octane, I use 93. Not an apples to apples comparison, I know, but both cars are within 3 months of each other in age (hers is newer than mine). Her's is a Honda, mine is an Acura (so essentially the same company). This has been true since for the last 6 years now (the cars were bought new and are just approaching 7 years in age).
Don't know if that makes or breaks the case for mileage claims with higher octane, but I've always had better mileage without question. Even on highway trips, I'm between 32-33mpg (3.2L, 260hp) and she is between 27-28mpg (3.0L, 200hp). I cruise at 75 to 80mph with a/c always on. Go a little slower with the Honda, but a/c always on as well...
 

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My nearby station is $2.79/2.89/2.99.

So homebrew 89 octane yields $2.856667 which means you save 3-4 cents/gallon.
 

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I have been running 87 with no ill effects.
I will be running several tanks of 91 to see if there is a mileage improvement, if there is, I will definatley be doing the math.

I'd definitely be interested in seeing the results of your research in this regard. Please report back when you find out something.

Thanks
BB
 

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Deliciously Blunt
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I have been running 87 with no ill effects.
I will be running several tanks of 91 to see if there is a mileage improvement, if there is, I will definatley be doing the math.

There probably won't be a mileage difference...not too sure though. Would be interesting to see.:) The engine is likely only mapped for 87 octane, and anything higher doesn't make it different/better, but it will extract another $$$ from your purse.

The Corvette is mapped for either 87 or 91 (runs best on 93) to put 89 in it is a waste, but if you put in 87, you won't get bad knocking, but you will get a decrease in ponies and torque, since it won't run as efficiently

Anyone has access to AvGas?:D
 

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A high compression ratio engine is the only reason you'd need anything higher than 87. Even still, an engine that requires 91 will usually run on 87 but igniting the gas earlier but you lose horsepower. On an engine designed to run on 87, you won't get any benefit from running higher octane.

Higher octane gas means that it can stand higher compression before it ignites from the compression. If you have a high compression engine that calls for 91, then the 87 could feasibly combust before the spark is introduced. However, most modern engines can recognize this and spark it before the compression ignites it but resulting in less power.
 

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This is going to get ugly.
:D :D


LIke just stated, octane gives you little or absolutely no power gain, if you believe this, you've fallen into the gas company's trap. It will give you minimul gains in MPG, not even close enough to get your money back on the extra dough put out at the pump. All higher octane does, is delay the ignition of the fuel in the combustion chamber. It has the exact same amount of power, just a delayed detonation.
If your truck is running bad, ie needs a tune up, then yes, you may see some gains in power and MPG, but, if you would tune it up, then the higher octane wouldn't be needed anyway.. Spark plugs are cheaper than filling up with 90+ everytime you get gas.
In short, unless your running forced induction, or have a high compression engine, don't waste the money, your computer will ultimately adjust the timing for optimum performance anyway, so it's a bust no matter what octane your running.

Stop wasting your money:eek:
Ask the turbo and S/C guys on here, they'll say the exact same thing, why run it if you don't have to.
 

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This is going to get ugly.
Hehe, you called it...

Octane is an additive to fuel that increases the temperature of combustion. The reason it is required is because as the cylinder pushes upward during the compression stroke the temperature of the air-fuel mix is raised proportional to to the increase in pressure. In some instances the temperature can be raised above the flash point of the mixture thus spontaneously combusting or pre-detonating (aka. knocking, pinging, detonation, etc.) before the cylinder reaches top dead center, and before the spark plug has a chance to fire and detonate the mixture on time. This results in catastrophically high cylinder pressures as the air-fuel mix is expanding while the piston is compressing the combustion chamber. Depending on how early the detonation occurs, and how much combusts, it can range from a minor problem resulting in poorer fuel mileage to catastrophic engine failure.

Now, the reason there are varying levels of octane are because cars come with different compression ratios. A high compression ratio is characteristic of a high performance engine which is why expensive cars usually require higher octane fuel. Higher octane does NOT mean higher power. The additional power comes from the increase in compression ratio (due to piston compression, or air compression from a turbo or supercharger).

DO NOT run higher octane in your engine than is required. You will see absolutely no increase in power or response and in some cases you may acutally lose power. Engines these days are controlled by complex computers that read internal knock sensors in the engine. If pre-detonation is sensed, it will retard timing and increase fuel (which saps power) automatically. Detonation is more likely to occur at high rpms and on very hot days, although if the wrong fuel is put in it could happen anytime :D :tu:
 
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