Posted by Mark (IP: 161.160.61.44) on August 05, 1999 at 18:03:49:
In Reply to: The Great Lie..... posted by TBR on August 05, 1999 at 15:43:58:
High Octane -- Is it Worth the Price?
What is octane?
Octane actually has two definitions.
One is chemical: Octane is a flammable hydrocarbon liquid that along with other hydrocarbons -- pentane, hexane, heptane, and many others -- is refined from crude oil and makes up the blend of chemical components called gasoline.
A second definition: Octane is a measure of a fuel's tendency to knock or ping when it is mixed with air and burned in the cylinder of an engine. This octane rating is not based on the amount of chemical octane in the gasoline. It is called octane because pure hydrocarbon octane is used as a knock standard, with a rating of 100. Gasoline, made from a blend of octane and other hydrocarbons, may have a higher or lower rating, depending on its tendency to knock.
How is octane rating determined?
Gasoline is subjected to two testing methods to establish its octane rating: one, called the motor method, runs the gasoline in an engine under load; and a second, the research method, runs the gasoline in a free running engine. The research method gives slightly higher ratings, and the octane number displayed on the pumps is an average of the two methods.
Octane facts
Knock occurs when cylinder pressures are high. It is normal for an engine to ping a little at full throttle because cylinder pressures are very high at full throttle. Engine knock, however, should not be ignored since it can result in serious damage to the engine.
High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high.
If your engine runs well and does not knock or ping on low octane gasoline, there is no advantage in switching to higher octane gasoline.
If your engine knocks or pings, it does not necessarily mean something is wrong with the gasoline. It could be a problem with the car's ignition timing or exhaust gas recirculation. On high mileage engines, a carbon build-up in the cylinders can increase cylinder pressures and cause knock.
Many of today's new cars have fuel-injected engines that need, at least periodically, to use gasoline with a detergent additive. They do not need high octane gasoline unless the auto manufacturer recommends it. Some gas stations, however, have detergent only in their high octane gasoline. If this is the only way you can get a detergent additive, you may want to buy high octane gas occasionally.
Always follow the auto manufacturer's recommendations in your owner's manual.
Octane myths
High octane gasoline improves mileage.
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that a tune-up will give you the same improvement on 87 octane gasoline.
High octane gasoline gives quicker starting.
No, it doesn't.
High octane gasoline increases power.
If your car is designed to run on 87 octane gasoline, you shouldn't notice any more power on high octane gasoline. Again, if it does make a noticeable difference, you may need a tune-up.
High octane gasoline has been refined more -- it is just a better product.
Additional refining steps are used to increase the octane; however, these additional steps do not make the gasoline any cleaner or better. They just yield a different blend of hydrocarbons that burn more slowly. The additional steps also increase the price.