ShadowDrake

Maybe if it were a diesel engine Please don't spread misinformation.

uberstang1

Just use what ford recommends, I had to switch to higher grade because the manual says 92octane for 4v

mustang gtizzle

I see a lot of people saying it's a waste or it hurts your car, but can anyone actually explain why? I've wondered about this too and I'd like to hear from someone who has a explanation from theory. It looks obvious to me that the higher quality the fuel, the better it is for your car but my ears are open to the truth.

ShadowDrake

Higher octane simple resists pre-ignition... it burns all the same once ignition has begun. Octane rating has nothing to do with quality... like I said, simply, octane = resistance to pre-ignition.

Edit: Corrected typo. And, here, to dispel myths further... because some people just remain ignorant.

Explains why unleaded fuels are never above 100 octane, and why fuels above 100 octane are leaded only.

Cornbread01

its better to run 87 unless you have some serous mod ex s/c nos or have a tune

GT_Bob

What do those octane numbers mean on the gas pumps at the station as you fill up your 'Stang? Why does it cost more for higher octane fuel? What is octane and why do some say 92 octane is better than 87 octane? These are all questions many people ask, and often time they are lead to false conclusions.

So, what is octane? Simply put, octane is a measure of gasoline's ability to resist ignition under compression. That spontaneous ignition is often referred to as "pinging" or "knocking", and those words describe well what it will sound like. The higher the octane, the more compressed the fuel can be before detonation/knocking.

However, this is not all that octane is. Going further in-depth, we come to see that octane is more than a rating, it's a hydrocarbon. Like other hydrocarbons (methane, propane, butane, and heptane), its chemical composition includes carbon atoms. The exact composition of octane consists of eight carbon atoms and eighteen hydrogen atoms, scientifically written out as C8H18. A fuel with a 100 octane (100% octane) resists detonation/knocking extremely well. Because of that, all fuels are compared to the 100% octane bench mark, and thus, an octane rating can be obtained. Transversely, heptane, another hydrocarbon, resists detonation very poorly and will spontaneously combust under even the smallest amounts of compression. This poor ability to resist combustion under compression gives heptane an octane rating of zero, and thus, makes heptane the other bench mark for determining a fuels octane rating. For example, a fuel with 89% octane would have an octane rating of 89 and a fuel with a 11% heptane will also have an octane rating of 89. However, this does not mean that the 89 octane you use to fill up your 'Stang is composed of 89% octane and 11% heptane. It just simply means that a fuel composed of 89% octane detonates under the same compression as a fuel composed of 11% heptane under the same circumstances. And as if you weren't confused already, those octane numbers at the pump don't tell you exactly what octane of fuel you are putting into your gas tank. The octane labels at gas station pumps, monitored by the United States Cost of Living Council, are actually an average of two octane ratings. This is because fuels react differently under certain circumstances. The two main circumstances being used in an engine under free-running conditions, and being used in an engine under load. These two octane ratings are derived from the motor method rating, where the engine is tested under load-bearing conditions, and a research method rating, where the engine is free-running.

Now that we know what octane is, why is it that some describe a 92 octane fuel as being more beneficial or better than an 87 octane fuel? Often times, this is a misconception. There is no real benefit to running a 92 octane in an engine that is designed for, and to work with, an 87 octane. However, depending on the engine and its configuration, you may be required to run a 92 or even higher octane rated fuel. The higher octane fuel is required for engines running higher compressions, at higher temperatures, and with more advanced ignition timing. But does this mean you can't run a 92 octane in your engine with a recommended octane of 87? No, you can, but there really isn't any benefit to it unless you have advanced your timing or are running under forced induction (supercharger, turbocharger, etc.). In fact, all you are doing is wasting money. You won't experience any increases in horsepower or torque (unless you are already experiencing detonation/knocking), it doesn't burn cleaner, and it doesn't give you better fuel economy.

So, if higher octane gasoline doesn't really benefit anyone other than allowing engines that require higher octane to run correctly, why does it cost more at the pump? Answer to this is simple. The higher the octane, the more time and money it takes to process the gasoline to achieve that higher octane. These extra refining steps don't make the fuel any better though, which is what often leads most to believe that it is better for your car to run a higher octane than needed. All that the refining companies are doing is creating a gasoline that will allow those who have cars with engines that require the higher octane to run correctly, and that is why it costs more.

We've come to the conclusion that 100 octane means that the fuel can resist spontaneous combustion extremely well, but how is it possible to have fuels with an octane rating of 100+? One method that is done in the refineries to create race and airplane fuels is to include certain additives such as tetraethyl lead that increase the engine's ability to operate under higher compressions without detonating. However, some companies have begun developing items known as "Octane Boosters" that increase the octane rating of your gasoline. These octane boosters can be purchased for relatively little money from automotive parts stores and the gas stations themselves. The only major drawback to these octane boosters is that the higher octane you are already running from the pump (such as a 92 or 93 octane), the less of an octance increase you will see.

At this point, I hope you've come to realize that you don't need or want to run a higher octane fuel than is needed. The myths about what octane is and what it does have been put to rest and the scientific truth has been shown.

mustang gtizzle

Wow GT_Bob I read your entire post and it had everything I was looking for. I'm not sure whether you wrote that yourself or if you got it from somewhere, but great job posting!

shuribob

++++1

mustang gtizzle

I didn't want to make my own thread for this so I thought I'd post here. I misplaced my owner's manual for my 2002 GT and I am forgetting what grade octane it says is required. 87? 89? If someone knows that would be great.

stang2000

DAMN, screw that, lol. Although if I had to pay the $3.89 I would. We've dropped considerably in IL. Down to $2.48 for 87 and $2.76(I get .03 cents off - $2.73)) for my 93 at Shell.