What is the actual difference between regular and premium gasoline?

[Cluricaun]

I know that the octane rating is higher, but I don’t know what that means. Is there more actual gasoline in the premium and that’s why it’s better? Help me understand why premium is as of this morning $.20 “better” than the regular stuff that I buy.

[What Exit?]

I remember reading this article by Cecil Adams

A small quote from said:

Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug.

[Cluricaun]

Ok, I grok that. But who still get's engine knock or pings? I've not heard of that actually being a huge problem on cars since the early 80's.

[What Exit?]

Ok, I grok that. But who still get's engine knock or pings? I've not heard of that actually being a huge problem on cars since the early 80's.

Read the rest of the article and Cecil talks about that to. Sensors to prevent ping and more.

[Glazer]

Higher octane burns slower. It is easier on your engine because it delivers power over a longer time. rather than all at once. Engins tuned for premiun deliver more power by taking advantige of a longer power stroke.

[Oliveloaf]

Higher octane burns slower. It is easier on your engine because it delivers power over a longer time. rather than all at once. Engins tuned for premiun deliver more power by taking advantige of a longer power stroke.

What he said.

No engines knock or ping anymore, because the engine management system can compensate for the low-octane fuel, but the result is reduced power and
potentially lower fuel economy.

If you always ran regular in your premium-needing car, you would likely never no the difference.

That said, some brands add additional detergents and other cleaners to their premium blends. BP, Mobil, Shell and Chevron all do, I believe. This is why
some mechanics recommend using the good stuff once every few tankfuls.

[Cluricaun]

So then in premium gas more, er, gassier?

[Glazer]

No regular is more gassier (vapor).

[robby]

...That said, some brands add additional detergents and other cleaners to their premium blends. BP, Mobil, Shell and Chevron all do, I believe. This is why some mechanics recommend using the good stuff once every few tankfuls.

This is a myth. Federal regulations require that detergents and other additives must be added to all grades of gasoline, and in practice, there is absolutely no difference between the additives added to lower-octane fuels and higher-octane fuels.

The octane rating of a fuel is a measure of only one thing--how hot the fuel can get before it ignites. In chemical terms, a higher octane rating corresponds to higher activation energies. High-compression engines compress the fuel-air mixture to a greater extent than lower-compression engines, so a higher octane rating may be necessary to prevent pre-ignition of the fuel before the spark plug ignites the fuel.

There is no significant difference in burn rate or power between the different grades of fuel.

The reason that higher-octane fuels cost more is simply because it takes additional steps in the refinery (e.g. increasing the branching of the hydrocarbons) to increase the octane rating.

If your engine does not require a higher-octane fuel, it is a complete waste of money. Unnecessarily "treating" your engine to higher grades of gasoline is simply "treating" the oil company to more of your money.

Great info here:
Car Talk: Premium vs. Regular FAQ

[Cluricaun]

I get it now, thanks robby.

[Scumpup]

...That said, some brands add additional detergents and other cleaners to their premium blends. BP, Mobil, Shell and Chevron all do, I believe. This is why some mechanics recommend using the good stuff once every few tankfuls.

This is a myth. Federal regulations require that detergents and other additives must be added to all grades of gasoline, and in practice, there is absolutely no difference between the additives added to lower-octane fuels and higher-octane fuels.

The folks over at Car Talk disagree with you. Whether or not the additional additives are necessary seems to be questionable, but the higher grades of gas from the tier 2 makers do contain additional additives.