[MNBoxster]

@Steven Choi,



Sorry to tell you but, Octane rating and Energy Content (Calorific Value) are two totally different things.

The Gas you're buying is a waste of money as any percieved power increase is merely a Placebo Effect. Also, mixing various Octane rated fuels rarely works because these have different densities and don't easily mix. Park your car for just an hour and the various fuels separate.

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites, it has nothing to do with how much energy it contains.

When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can severly damage an engine because the pressure built-up from this explosion creates a shock wave that can actually shatter internal components. 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 or it will knock. 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." Using a higher rated gasoline than your engine calls for is wasted because the engine never reaches a compression which might trigger knock. You should use the lowest Octane fuel which your engine can smoothly run on without knocking.

Gasoline is what is called a Aliphatic Hydrocarbon meaning that it is composed only of Carbon and Hydrogen molecules arranged in chains of varying lengths. These different lengths display different properties when burned.

The primary components of Gasoline are: Heptane and Octane. These are molecules of Carbon and Hydrogen and get their names from the number of Carbon Atoms chained together in the molecules (7 for Heptane and 8 for Octane).

Heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane, on the other hand, handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent 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.

In Simple terms, the octane rating of a fuel is determined by running it through a very special Test Engine costing in excess of $300,000. This Test Engine is a single cylinder engine in which the cylinder volume can be varied to create different pressures (variable compression). Two fuel sources drive this engine. One is pure Heptane, while the other is pure Octane (or an Octane mixed with other Hydrocarbons). These fuels are simultaneously introduced at varying combinations until knock is induced in the engine. Then, the ratio of Heptane to Octane is recorded and this is the Octane rating.

So, the Octane Rating is the % of Octane contained in the fuel. For example: Octane makes up 87% of the fuel in 87 Octane gas while Heptane makes up approx 13% and so on.

To prevent fouling, lower emissions and types of emissions and to promote smooth burning, other HydroCarbons are also used such as an additive named MTBE.

MTBE is short for methyl tertiary butyl ether, a fairly simple molecule that is created from methanol. MTBE gets added to gasoline for two reasons:
First, it boosts the octane rating, Second, it is an oxygenate, meaning that it adds oxygen to the reaction when it burns. Ideally, an oxygenate also reduces the amount of unburned hydrocarbons and carbon monoxide in the exhaust. Gasoline can contain as much as 10 percent to 15 percent MTBE, substituting it for Iso-Octane.

Now the bad news, because most Gasolines use Hydrocarbon Molecules with roughly the same Carbon to Hydrogen ratios, the Calorific Values (Energy Content) are pretty much the same. Some additives, such as Toluene can increase power, but these are restricted by Law as to the amount the fuel can contain because of their toxicity or polluting qualities.

Also, using very high Octane rated fuels in a modern engine can confuse the ECU which is set for specific parameters. Thus, if it reads a Sulpher, Oxygen or CO² content in it's sampling which is outside it's parameters, it can actually reduce HP or Torque by limiting fuel, advancing/retarding the timing or intake air.

All you're really doing is probably polluting the air more and spending more money. The best thing you can do is stick to the Octane Ratings suggested by the Manufacturer and buy the fuel from the busiest Station you can to insure both it's freshness (yes - gasoline ages and Octane can drop as much as 2-3 points) and it's purity (because busier Stations empty their tanks on a more regular basis reducing the amount of corrosion, contaminates and moisture the gasoline absorbes). Hope this helps...

Happy Motoring!...Jim'99