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Facts for Consumers
PDF Version (http://www.ftc.gov/bcp/conline/pubs/autos/octane.pdf)
http://www.ftc.gov/images/pdf_get_adobe_reader.gif (http://www.adobe.com/products/acrobat/readstep2.html)The Low-Down on High Octane Gasoline :

Are you tempted to buy a high octane gasoline for your car because you want to improve its performance?

If so, take note: the recommended gasoline for most cars is regular octane.

In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit.

It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.
Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.
What are octane ratings?
Octane ratings measure 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.
What's the right octane level for your car?
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.
How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.
Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.
Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.
Is knocking harmful?
Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.
Is all "premium" or "regular" gasoline the same?
The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

For More Information
If you're concerned about the accuracy of an octane label - or if you don't see a yellow octane sticker on a gasoline pump, write: Consumer Response Center, Federal Trade Commission, Washington, DC 20580.
The FTC works for the consumer to prevent fraudulent, deceptive and unfair business practices in the marketplace and to provide information to help consumers spot, stop and avoid them. To file a complaint (https://rn.ftc.gov/dod/wsolcq$.startup?Z_ORG_CODE=PU01) or to get free information on consumer issues (http://www.ftc.gov/ftc/consumer.htm), visit www.ftc.gov (http://www.ftc.gov/) or call toll-free, 1-877-FTC-HELP (1-877-382-4357); TTY: 1-866-653-4261. The FTC enters Internet, telemarketing, identity theft and other fraud-related complaints into Consumer Sentinel (http://www.consumer.gov/sentinel), a secure, online database available to hundreds of civil and criminal law enforcement agencies in the U.S. and abroad.



http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm (http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm)

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel

I don't agree with that statement. If your engine knocks on the recommended fuel, there is something out of factory specifications. On old points style ignition, reset your timing and it would cure it. Now ignition timing is controlled by several sensors and one or more computers.
Cars today have a knock sensor that take care of octane requirements.
Our 2000 Nissan Maxima required a minimum of 92 octane. It may have had 6 tanks of premium ran through it in the 114,000 miles while we had it. No knocks or pings, (just parking lot dings).:rolleyes:

I changed the plugs at 102,000 miles for the first time. They needed it.

excellent find tiger! a word from the goverement is the word that will convince us all...

msirach. The car may not knock, but the car may retard the timing or do other things making it run less efficiently.

I'm not trying to be negative, but I think thats what happenst.

Does anyone know the consequences of retarding timing and doing things to make your car not nock because of lower octane?

msirach. The car may not knock, but the car may retard the timing or do other things making it run less efficiently.

I'm not trying to be negative, but I think thats what happenst.

Does anyone know the consequences of retarding timing and doing things to make your car not nock because of lower octane?
Tom,

The correct reply to this is as follows:

Even a modern 2006 Chevy Corvette Z06 with 505 HP can in an (Emergency) run on 87-Octane. However it points out {Do-Not Run Wide Open Throttle}.

Almost all "Older as well as New" vehicles can Burn-87-Octane even if they recommend 91/93-Octane Gas.

As (You) pointed out in your Post above the results are:

Less Power
Decreased Ignition Timing
Another often {Missed} result of burning 87-Octane is "Increased Heat" due to the 87-Octane Gas having a much Higher {Flashpoint} for Ignition.


Just because one can get away with Burning Lower Octane Gas does not mean "You-Should". If the vehicle states to burn 91/93 Preminum Gas the Manufacture had a Very good reason to recommend using it. Manufactures Do-Not get a {Kick-Back} from the Oil Companies to recommend using higher grade gas than the vehicle actually needs. This should I think be very apparent with the price of all Fuels these days.


Hope this clears this up for anyone not more Familiar with why you {Don'T} use lower grade gas in your Vehicle than recommended.

Terry (tiger)

Intresting this comes up.

Seeing that my Civic has a 9.5:1 compression I ran some 91 thru it this summer. Honda goes to great pains to keep a boarderline high compression ratio engine on 87. They use the computer tricks and oil nozzels that spray up in the under side of the piston dome to help with cooling. And lord only knows what else.

The results where intresting IMO. On 91 it ran like a diff. car in the cool of the morning. It pulled the A/C alot better without the hord mpg hit I see on 87. About 2 mpg better over all. It was alot more peppy, quiter.

The afternoon temps in the low 100's produced bad things on 91. The car became very sluggish, A/C mpg plumited to far worse than 87 in normal running.

So it would appear that 91 would be worth looking into for winter month's usage in my car. But will never be used in the summer again. I ran about 6 or 7 tanks thru the car to come up with this seat of the pants data. It was amazing how the car reacted to the fuel change.

You experiance will differ. :)

You are right about the fuel/knock. In higher compression engines, they are more prone to ping. The lower octane fuel will actually ignite under compression before the plug fires. It was late last night when I posted and I missed the point I was trying to make.
The article says to increase octane if your car pings.
If you do that you are spending more on fuel than you need to and the change in the performance of your car that is causing the ping has not been repaired.

Psyshack, that's a really interesting result. In some ways it's completely the opposite of what I would have expected. Running really well in the morning makes sense, since cooler air reduces the potential for pinging/preignition. It would seem that you are right about that R18 wanting a higher octane fuel to help it cope with the relatively high compression ratio. But your experience in the hot afternoon is a little baffling. If the car is going to retard ignition and bog down, one would think that it would be worse on 87 than on 91. The better bulk ignition resistance of higher octane fuel ought to make up somewhat for all that extra latent energy in the hot air/fuel mixture. I wonder what's going on?

Psyshack, that's a really interesting result. In some ways it's completely the opposite of what I would have expected. Running really well in the morning makes sense, since cooler air reduces the potential for pinging/preignition. It would seem that you are right about that R18 wanting a higher octane fuel to help it cope with the relatively high compression ratio. But your experience in the hot afternoon is a little baffling. If the car is going to retard ignition and bog down, one would think that it would be worse on 87 than on 91. The better bulk ignition resistance of higher octane fuel ought to make up somewhat for all that extra latent energy in the hot air/fuel mixture. I wonder what's going on?

Brick

I dont know what was going on. It was very apprent tho. Much improved car in the mornings. Afternoon heat ,,, it drove like my old Festiva. It was like night and day.

Returning to 87 the diff. was seen in 20 miles or so. Back to normal in the cool of the morning and heat of the afternoon.

I will revist this during the winter months and see what happens.

Also will be playing with WAI durning the fall and winter months.