Its all in the computer and how it reads the emisions and the wrong octane gas actually confuses older computers when trying to calculate the emissions. and thus it changes the settings and your car runs worse.

All this talkabout flame burn and stuff is just looking for a complicated technical answer for a simple problem. Ignore all hte engineer types and but 87 gas and smile when saving the money.

Besides then you can say, "Your V8 was beat by two triangles on 87 pump gas" :D

Hey now.... where would you be without all the engineers...And I'm still sticking with NO7Yet on the compression thing. A longer hydrocarbon chain is more stable than smaller chains so it makes sense that a mixture with more or a stable substance can handle more compression.

Aaron

Well with out engineers we would be walking :D

But I said engineer types not engineers :D

But its still in the programming of the computer for emissions. Its programed for 87 octane and my putting 93 in it it has changed the numbers of the hydrocarbons hitting the O2 sensor and that diffence confuses its simple porgramming logic so it trys to compensate by adjusting the fuel flow and thus your car leans out or runs rich and thus Watson it runs worse runs worse. Ultimatly its all this burn length but how many people out side race teams measure the time of the burn in the combustion chamber???

Unless you can change the programing in the CPU you cant really begin worrying about burn times of the octane molecules. uless you like fretting over things you cant change.

I've done a lot of research on this and, as previously stated, the only difference between octane levels is the likelihood of premature ignition.

High compression engines (turbo or not) compress the fuel air mixture more than a lower compression engine. A gas mixture under high compression will, all else equal, ignite at a lower temperature than a mixture at a lower pressure. Sometimes, ignition occurs even BEFORE the spark plug generates a spark. This is called premature ignition. Premature ignition results in "pinging," "spark-knock," or whatever you want to call it - it is a direct result of the high combustion chamber pressure of some engines.

While there are a couple different ways to prevent this premature ignition, it is easiest to just use a fuel with a higher flash point. 92 octane gas has a higher flash point than 87 octane. That is the ONLY difference between the gas. They all have detergents. They all have the same addititives. The gas companies don't advertise this generally, but the only significant difference chemically is the added octane.

Regarding the burn-time of the mixture, the spark from the spark plug greatly exceeds the flash point of either gas mixture (87 or 92). Therefore, both will ignite at the same time when the spark occurs. All you are doing with higher octane is preventing the gas from igniting BEFORE the spark occurs. I don't know if 92 octane gas burns slightly slower than 87. I doubt it because once the flash point is exceeded by a large amount, then the mixture will ignite very quickly, even if it is higher octane. But even if it is slightly slower, it is negligible and won't make a difference in the performance of your car.

The bottom line is, if your car is pinging, use higher octane. If not, use what the owner's manual says. Should you use a higher octane anyway, just in case? Well, if you want to, it's probably not going to hurt your car, but it is more expensive and, at best, you will just be throwing away money.

Now, as an aside, there IS a difference between some gasolines. Specifically, no-name gas is not as good as name-brand gasoline. Even though the truck that delivers to the Exxon station will also deliver the same gas to the no-name station, the fact is that it will deliver to the Exxon station first and the gas will meet more stringent quality control criteria. This is why it's more expensive than no name gas. The truck will deliver to the no name station last and, therefore, there is a higher concentration of foreign particles in the gas. It is cheaper because the quality control is not as high. So, stay away from no-name stations. There are also differences between name-brand gas (e.g., Exxon uses more dyes in the gas), but most of these differences are probably not significant enough to worry about.

Dave

STOP THE MADNESS!!!!!!!!
 

I'll refrain from commeting on what engine SHOULD burn what octane...

What follows is an explanation of what octane is....

The octane rating of gasoline tells you the amount that the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want have happening. Lower octane gas (like "regular" 87 octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high performance engine" has a higher compression ratio and requires higher octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance". The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact. When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has 5, hexane has 6, heptane has 7 and octane has 8 carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. 87 octane gasoline is gasoline that contains 87% octane and 13% heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are: 1) the fact that lead clogs a catalytic converter and renders it inoperable within minutes, and 2) the fact that the earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans). When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jets burn kerosene, by the way).

Sniper_X
Always Tinkering :stick: