Gas Grade...

[Icecobra]

Ice, I get more mpg running 91 10% ethanol than I do running 87 10% ethanol, usually 1-2 mpg, I also get 14 mpg flooring it everywhere, other people running 87 usually get 13 driving normally, I can also get well over 20 on the freeway keeping a constant 65 mph, obviously octane has effected my gas mileage, and your truck WILL make more power with a higher octane fuel, that alone is worth the extra cost in my opinion

You think you do but if you actually ran a real test on it drove the exact same distance the exact same way you would find you get exactly the same. Time of day, wind, how you accelerate, how hot it is, barometric pressure will change your fuel by 10% I have done this test I know.,... 10% is not a factor from 87 to 91 octane... to get a real world test try it Myth busters style... Get a track and drive around it for 5 days using different drivers and change fuel at the half way point.... Your variable will be almost nothing for fuel type and as much as 20% based on driver...... The facts are the 87 to 91 yields the same BTU value either way.....

 

[Nick@Apollo-Optics]

You think you do but if you actually ran a real test on it drove the exact same distance the exact same way you would find you get exactly the same. Time of day, wind, how you accelerate, how hot it is, barometric pressure will change your fuel by 10% I have done this test I know.,... 10% is not a factor from 87 to 91 octane... to get a real world test try it Myth busters style... Get a track and drive around it for 5 days using different drivers and change fuel at the half way point.... Your variable will be almost nothing for fuel type and as much as 20% based on driver...... The facts are the 87 to 91 yields the same BTU value either way.....

Okay. So it has the same BTU. Then why do high performance motors use higher octane fuel?

Why do race cars use C116 fuel?

 

[Icecobra]

Okay. So it has the same BTU. Then why do high performance motors use higher octane fuel?

Why do race cars use C116 fuel?

Because of higher combustion chamber ratios... When you step it up and run 15 to 1 compression regular fuel will ignite at different rates uncontrollably. You will get one stroke it ignites 20 degrees early and the next stroke 15 degrees and so on. The octane helps control pre-ignition on high compression motors. Pre-ignition issues are why jets run kerosene not gasoline... You have to be able to control exactly when the bang happens on gasoline motors... This is where octane comes in...

 

[Cleave]

The difference is how the fuels burn rich, 91 will burn more completely than 87, which is why it burns longer and produces more horsepower but no extra torque, this also means less fuel is needed per stroke to produce the same amount of power, all fuels burn incompletely during every stroke, the difference is how much of it burns incompletely

 

[Icecobra]

What your looking for is how you get more BTU out of the fuel in the combustion chamber, you cant. One ounce will yield only x BTU, in drag racing and high compression motors you cram more fuel, BTU is increased by adding more fuel and air. At 17to1 you have doubled the amount of fuel air mixture in the combustion chamber so you double the expected BTU amount... Not by magic in fuel but simply adding more fuel... Octane allows you to compress the fuel more without the fuel going boom at the wrong time.... The higher the octane the higher the compression ratio......

---------- Post added at 02:35 PM ---------- Previous post was at 02:34 PM ----------

The difference is how the fuels burn rich, 91 will burn more completely than 87, which is why it burns longer and produces more horsepower but no extra torque, this also means less fuel is needed per stroke to produce the same amount of power, all fuels burn incompletely during every stroke, the difference is how much of it burns incompletely

Octane has zero to do with how much of the fuel burns....

---------- Post added at 02:36 PM ---------- Previous post was at 02:35 PM ----------

Fuel burns in the combustion chamber at a predicable rate based on known factors of the combustion chamber....

 

[Cleave]

It's not magic, it's efficiency, and it's why modern engines can produce 662 horsepower and get 22 mpg on the freeway

---------- Post added at 02:40 PM ---------- Previous post was at 02:38 PM ----------

No, fuel does not, every stroke of a piston produces varying amounts of power, this is due to the fact that perfect combustion is impossible and you will never get every drop of fuel to burn exactly how you want it to

 

[Nick@Apollo-Optics]

Compression ratios have to do with timing correct? So, if the computer can sense changes in the octane level and advance the timing for higher octane...wouldn't this yield more power?

 

[Icecobra]

It's not magic, it's efficiency, and it's why modern engines can produce 662 horsepower and get 22 mpg on the freeway

---------- Post added at 02:40 PM ---------- Previous post was at 02:38 PM ----------

No, fuel does not, every stroke of a piston produces varying amounts of power, this is due to the fact that perfect combustion is impossible and you will never get every drop of fuel to burn exactly how you want it to

And Octane plays no part in burning efficiency of fuel..... It is determined by timing and compression... Octane helps with higher compression engines like I used to run years ago.... But today FORD and other Manufacturers try to burn as completely as possible due to more stringent EPA standards... So octane does not effect fuel efficiency or every one would require 99 Octane if it were the deciding factor in fuel burning... In fuel everything plays its part and octane helps prevent pre-ignition or fuel going boom in the combustion chamber at less than optimal time.... It is just how it works....

---------- Post added at 03:02 PM ---------- Previous post was at 02:53 PM ----------

Compression ratios have to do with timing correct? So, if the computer can sense changes in the octane level and advance the timing for higher octane...wouldn't this yield more power?

If Ford were allowed to setup timing parameters to cover a wide ratio then it could if you could get a higher compression... If it is at peak compression and Ford has to put in safety factors, if the timing would adjust far enough, if you had a sensor in the tank to determine octane and you could control external factors, such as temperature, driver, moisture content of the air, etc. The simple truth Ford set up these trucks with 9to1 compression. You can not change that factor with out adding a way to increase the amount of fuel. Hence why people with super charged engines find they get more horsepower by increasing the amount of the fuel in the combustion chamber. But have to run higher octane gas.... HAVE TO..... If you get a tuner and adjust the timing, they tell you to get 93 octane fuel to wait for it... STOP PRE-IGNITION, which we now know means the fuel ignites at the wrong time on its own, because we adjusted timing outside Fords recommended range.... So in the end Octane plays a part..... in stopping knock or ping caused by fuel being ignited by compression...

 

[Nick@Apollo-Optics]

And Octane plays no part in burning efficiency of fuel..... It is determined by timing and compression... Octane helps with higher compression engines like I used to run years ago.... But today FORD and other Manufacturers try to burn as completely as possible due to more stringent EPA standards... So octane does not effect fuel efficiency or every one would require 99 Octane if it were the deciding factor in fuel burning... In fuel everything plays its part and octane helps prevent pre-ignition or fuel going boom in the combustion chamber at less than optimal time.... It is just how it works....

---------- Post added at 03:02 PM ---------- Previous post was at 02:53 PM ----------



If Ford were allowed to setup timing parameters to cover a wide ratio then it could if you could get a higher compression... If it is at peak compression and Ford has to put in safety factors, if the timing would adjust far enough, if you had a sensor in the tank to determine octane and you could control external factors, such as temperature, driver, moisture content of the air, etc. The simple truth Ford set up these trucks with 9to1 compression. You can not change that factor with out adding a way to increase the amount of fuel. Hence why people with super charged engines find they get more horsepower by increasing the amount of the fuel in the combustion chamber. But have to run higher octane gas.... HAVE TO..... If you get a tuner and adjust the timing, they tell you to get 93 octane fuel to wait for it... STOP PRE-IGNITION, which we now know means the fuel ignites at the wrong time on its own, because we adjusted timing outside Fords recommended range.... So in the end Octane plays a part..... in stopping knock or ping caused by fuel being ignited by compression...

Interesting. I guess my last question is how does Ford claim a +10hp bump in the owner's manual going from 87 to 91 octane?

 

[Cleave]

And you think that just because the entire cylinder worth of fuel doesn't go off at the wrong time that individual drops of fuel don't as well? Every time the piston goes through a power stroke there are small amounts of misfire, higher octane fuel helps to lessen the amount of misfire because it is more stable, which is why it has to be used in higher compression ratio engines to prevent pre-ignition, this increases the usable amount of fuel in the cylinder, which means you can get more power out of each power stroke, it doesn't matter whether you're running 8:1 compression or 12:1 compression, better (more stable) fuel always helps