What gas rating to use?, Kind of random Options

[Chanh55]

Hey '94 GT owner, just wondering what gas rating you guys use. I've been using 87 and I think it's causing my engine to knock, so should I drive it untill its empty and start using 91?

[hioctane]

This is from http://www.toyotacelicas.com/information/c...e/gasmyths.html

Using 91+ octane gas in a celica = waste of gas unless it's boosting.

Premium Gas Myths

Many people believe that “premium” gas is the best gas. Not true. Premium simply means “premium price” for higher octane. Octane is a simple measurement for a gasoline’s ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders.

Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump. The misnomer about octane is that the higher the rating, the better or more smoothly your car will run. In fact, premium gas can be bad for your engine if it was not designed to run at a high-octane level.

Although it may seem that the term “premium” or “high octane” implies that more energy is available, premium gas does not produce more energy than regular or mid-grade fuel. The octane grades are designed to accommodate engines with different compression ratios. High compression engines, found in most performance cars, require a fuel that burns efficiently at a higher temperature. That’s what premium fuel does, it burns hot under high compression. In a normal engine, premium fuel does not burn completely, resulting in excess carbon build-up and carbon fouling of the spark plugs. The end result is a less efficient engine that requires tune-ups more frequently. Oh, yeah, did I mention it also wastes money?

The only time you might need to switch to a higher octane fuel is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars. Check your owner’s manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.