more is better .

 

So running higher octane will not hurt a thing but if a tune is not present I thought it was pointless to run higher octane and pay for premium gas? Sounds like you are offsetting the benefits of running 87 octane (stock tune)while running a more expensive gas. JMO J

 

Definatley improves performance with high octane!! Proven by experience!![sm=happybounce.gif]

 

Dude.. dont fill up with leaded gas!!! you can clog up your cats and maybe screw up some other stuff

 

+1! Yeah, what he said [sm=exactly.gif]

 

I heard that running 93 on stock tune, will actually decrease about 5hp. I dont know...its something about higher octane burning slower or something. I always did (when stock) 89 octane to stop the slight ping, but never 93 since is 6 octane higher. I dont know tho...

 

After some research it looks like I was partially wrong and partially right, I apologize for the wrong part, at any rate I found thisarticle in Wikipedia.com that explains the effects of octane rating.

Effects of octane rating
Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).
Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitues the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics.
It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.
A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content on a volume basis (per litre or per gallon). The reason for this is that ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl radical for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. Note that to a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.
In the case of alcohol fuels, like Methanol and Ethanol, since they are partially oxidized fuels they need to be run at much richer mixtures than gasoline. As a consequence the total volume of fuel burned per cycle counter balances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred max power air fuel mixture of 12.5:1, it will release approximately 19,000 BTU (about 20 MJ) of energy, where ethanol run at its preferred max power mixture of 6.5:1 will liberate approximately 24,400 BTU (25.7 MJ), and Methanol at a 4.5:1 AFR liberates about 27,650 BTU (29.1 MJ).
To account for these differences, a measure called the fuel's specific energy is sometimes used. It is defined as the energy released per air fuel ratio. For the case of gasoline compared to the alcohol fuels the specific energys are as follows:



Fuel
Net energy
Units

Gasoline
2.92
MJ/kg

Ethanol
3.00
MJ/kg

Methanol
3.08
MJ/kg
Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure, which is a function of elevation and weather conditions.
Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved.
[font=arial]Many high-performanc

 

This is stolen from www.primemover.org

The octane number assigned to a motor fuel has very little to do with the actual chemical "octanes" in the fuel and everything to do with how well the fuel resists detonation (which is directly related to the amount of energy (heat) required to get the fuel burning in the first place).

Therefore, it is possible to assign octane VALUES to fuel which contain no octanes whatsoever.


WHY DO WE CARE ABOUT OCTANE? WHAT IS PREIGNITION? WHAT IS DETONATION?

The octane value of a fuel is an empirical measure of its ability to resist detonation and, to a limited extent, preignition. Technically, octane ratings measure a fuel's ability to resist the spontaneous ignition of unburnt end-gases under controlled test conditions.

What is preignition?

Preignition occurs when the fuel/air mixture in a cylinder ignites before the spark plug fires.
It can be caused by burning contaminates (such as carbon, or a spark plug of the wrong heat range) in the cylinder or by extreme overheating.

What is detonation?

Detonation occurs when the flame-front in a cylinder does not proceed smoothly from the point of ignition (the spark plug) to the opposite side of the cylinder.
It refers to the spontaneous ignition of the entire charge in the cylinder. This ignition is often caused by the extreme pressure rise in the cylinder that occurs when the charge is first ignited (by the spark plug).


WHAT ABOUT FUELS?

There are six things to consider when comparing hydrocarbon fuels:

1. Volatility. In short, what's the fuel's propensity to vaporize. This effects the ability to easily mix the fuel with air and the fuel's tendency to vapor-lock. It also determines the pollution characteristics of the fuel where evaporative pollution is a concern.
2. Pre-ignition & knock resistance. Referred to as "Octane value." How much energy does it take to get the fuel burning - how much does it resist auto-ignition from compressive heat? Also, what is the rate of burn of the fuel (which affects the rate of pressure rise)?
3. Energy content. How much energy can be extracted from the fuel as a percentage of its volume or mass.
4. Heat of evaporation.
5. Chemical stability, neutrality, and cleanliness. What additives does the fuel contain to retard gum formation? Prevent icing? Prevent corrosion? Reduce deposits?
6. Safety
The first three factors are often confused and interrelated when, in fact, they measure three completely separate things. There is no natural collelation between them.

General rules:

Heavy fuels (diesel, jet): Low volatility, low knock resistance, high energy per volume
Light fuels (gasoline): High volatility, high knock resistance, low energy per volume

Note that gasoline, partially, makes up for its (relatively) low energy-per gallon by the fact that a gallon of gasoline weighs less (by about 15%) than a gallon of jet fuel.

Octane rating is in no way correlated with engine power or efficiency. There is more potential energy in a gallon of diesel fuel than a gallon of gasoline, yet the diesel fuel has a much lower octane value (more on that below).


HOW DO YOU DETERMINE OCTANE?

Ok, then, how is octane rating determined? First, you go out and get a suitable supply of the fuel which you wish to test. Then, you get yourself some heptane (made from pine sap) and some iso-octane (a petroleum derivative). Finally, you and your buddies arbitrarily, agree that iso-octane has an octane rating of 100 while heptane has an octane rating of 0.

Next, you call up Waukesha Motors and order yourself an ASTM-CFR test engine. Make sure you have about $250,000 available on your VISA before you order it. This single-cylinder wonder has a four bowl carburetor and a movable cylinder head that can vary the compression ratio between 4:1 to 18:1 while the engine is running.

You fill the ASTM-CFR full of your mystery fuel and, for automotive fuels, you run two test protocols using the ASTM. One protocol is called the motor protocol and the other the research protocol. You vary the compression ratio until the onset of knock and write down all kinds of various scientific parameters.

Next, you run your reference fuel, made up of various proportions of heptane and iso-octane through the ASTM-CFR. You keep varying the proportion of heptane to iso-octane until you get a fuel that behaves just like (knock-wise) your mystery fuel. Once you get that, you say to yourself "How much heptane did I have to add to the iso-octane to get the mixture to knock in the ASTM-CFR just like my mystery fuel?" If the answer is, say, 10% heptane to 90% iso-octane, your mystery fuel has an octane number of 90.

How do the motor and research protocol differ? Mostly in input parameters. In the motor protocol (ASTM D2700-92), the input air temp is maintained at 38C, the ignition timing varies with compression ratio between 14 and 26 degrees BTDC, and the motor is run at 900 RPM. In the research protocol (ASTM D2699-92) the input air temperature varies between 20C and 52C (depending on barometric pressure), timing is fixed at 13 degrees BTDC, and the motor is run at 600RPM.

The motor method, developed in the 1920s, was the first octane rating method devised. After its introduction, many more methods were introduced. During the 1940s through the 1960s one of those methods, the research method, was found to more closely correlate with the fuels and vehicles then available. However, in the early 1970s automobiles running on high-speed roads, such as the German Autobahn, started destroying themselves from high-speed knock. It was found that the difference in ratings between the research and motor method, known as the fuel's sensitivity was important as well. The greater the fuel's sensitivity, the worse it performed from a knock point of view in demanding, real-world, applications.

Remember, at the pumps, the results of the motor and research numbers are averaged together to get the value you see. The fuel's sensitivity is not published. Highly cracked fuels have high sensitivity while paraffinic fuels often show near zero difference between the two. While the fuel's sensitivity is not published at the pump it can be a valuable indicator as to the fuel's real world octane performance. Remember, the octane tests are conducted in a lab using a special test engine; the lower the fuel's sensitivity, the more likely it is that the fuel will, indeed, behave as expected. Generally, the closer the fuel's research rating to the published rating the more reliable the published rating. Because the motor and research methods primarily differ in terms of input parameters (the test engine is the same for both), the greater difference that a fuel exhibits between its motor and research test will be due to differences in input parameters (intake temp, timing, etc.). A fuel that has an octane rating that varies with intake parameters is said to be more "sensitive."


HOW DO YOU DETERMINE AVIATION GASOLINE OCTANE?

The octane of aviation fuel is not measured in exactly the same was as is automobile fuel.

Once again, you start with your trusty ASTM-CFR engine. First you set up the ASTM-CFR for the motor method and use that method to determine the motor rating of your fuel. You then correct that rating to the "Aviation Lean" rating using a conversion table. Below about 110 motor octane (a performance number of 110), the aviation lean and motor octane numbers will differ by only about 1 or 2 points. Above 110 motor octane the differences can be significant. Next you pull out another version of the ASTM-CFR engine. This one has a fixed compression ratio but allows you to supercharge the intake manifold. You pressurize the intake to higher and higher values until the onset of knock. Other than that, the parameters are the same as for the motor method used for automobiles. The su