[NOTE: This was originally posted on May 16, 2003, on the blogger-based version of Corey's Ramblings. I'm starting to migrate entries of note over, and I was talking to a friend about this one, so I thought I'd go back and post it.]

Ever since I read the excellent overview of gasoline at cockeyed.com, and the gas prices jumped so dramatically, I've been using the lowest octane rated gasoline that I can buy, which means I'm also buying the cheapest and saving money. Hurra! Not wanting to just blindly follow someone's advice, which is what I usually do, I decided that I was going to start looking for more information on octane and whether or not it really does matter. Chevron, itself, has an article about octane which basically says that, unless you have a super fancy car, you can get away with low octane.
Apparently, higher octane gasoline was created to help older cars keep from 'knocking,' which is a problem that most newer cars don't have. Frankly, I've never heard my car 'knock,' except for the time that I slid into that guardrail, then I guess you could say there was a bit of a 'knocking' sound. My engine, though, doesn't seem to have any problem knocking (much prefering to just walk right in WAKA WAKA WAKA!).
The FTC has an article about octane which includes this great quote:
"Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. ...Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need."
Wow! Imagine that.
Further looking around led me to the always useful How Stuff Works and their article on octane. Further reading on that reveals that octane comes form the oil refining process. When the crude oil is "cracked" in a refinery, you end getting different length chains of hydrocarbon atoms. By separating these chains, you get different kinds of fuel, such as methane (one atom), butane (four atoms) and propane (three atoms). Well, continue to take longer chains of hydrocarbon atoms and you get even more kinds of fuel. They sort of ran out of cool names for the fuels, so they just relied on the standard prefixes for numbers, resulting in pentane, hexane, heptane and, the subject of our discussion, octane. Well, if you know how a car works, which I don't, then you know that one of the things a car does to the gasoline is compress it before putting the spark in to ignite it. Well, engine knocking occurs when the compression step (or "stroke" in car lingo) causes the fuel to ignite, rather than allowing it to wait for the spark from the sparkplug. This preignition is what causes the knocking. It turns out that heptane (7 atom chain) doesn't handle compression too well, so it preignites too much, causing your car engine to knock. Well, luckily, octane (8 atom chain) handles compression much better, much prefering to wait until the spark comes before it ignites. By combining heptane and octane together, you get different octane values. 87 grade fuel is 87 percent octane and 13 percent heptane, higher octane ratings work the same (92 is actually 92% octane and 8% heptane). As you can see, higher octane ratings will be more resistant to preignition through the compression stroke in your car's engine.
Most cars, apparently, are designed to run on 87 grade fuel, which means that increasing the octane rating of the gasoline you put in your car will not add any real benefit to your car. The major effect that you will get from it is a slightly lighter wallet. Of course, I always pay with a credit card at the pump, if I can, so I'm really just seeing a decrease in my bank account information.
After doing a bit of research, I've decided that I'm not going to switch back to higher octane even if the price comes down.
NOTE: Some high-performance sportscars are designed for higher octane gasoline. Make sure that you check your owner's manual for which fuel your car was designed for. You can try lower-rated gasoline and see if your car knocks. If not, then you are good to go on the money-saving track!
Disclaimer: I'm not a scientist, nor do I know anything substantial about cars. The information contained here is my own personal opinion based on research that I've done. Please check for yourself, as I'm in no way responsible for anything that may happen to your car based on your reaction to my posting here.

 

[Update: Apparently, Mary's old 1993 Chevy S-10, which has seen its share of much better days, actually does run better (read: at all) on higher octane gas. When we put 87 grade into it, the damn thing had a lot of trouble starting. I'm not saying that there is a definite correlation, as I also got it to start better for a while by replacing one of the cables to the distributor that was sparking.]