Gas: Is Higher Octane Worth The Cost? - The Definitive Answer... I Think

My SUV says 91 recommended but not required. I used regular when I first purchased the car and had the Oxygen sensors go out twice before the warranty expired. The dealer said the regular gas was causing the problem.
I have been using premium fuel for the past 4 years with no problems.

Octane ratings over the called for rating is no better for the car and generally will not increase mileage, might even have a negative effect. In general I don't believe in buying by brand either. In several places I've lived you can watch a local wholesale gas company deliver gas to a local "name brand" station, and then cross the street and deliver gas from the same tanker truck to a different "major brand" station.

One thing that will make a huge difference if you can find it is to get 100% gas and not the 10% alcohol crap. I noticed on a trip last year that some stations in a few mid-west states were adverting that their gas had no alcohol with large signs. Unfortunately, I'm unable to find that around where I live. But I have observed that when I can get a tank full of pure gasoline without alcohol that my mileage is much better. So much better, in fact, that that "up to 10% alcohol" that our government is mandating actually robs me of over 10% of the expected mileage! In other words, I would be better off just buying the 9/10 of a tank without the 1/10 alcohol and paying for a full tank of gas and letting them keep the alcohol.

Unfortunately, we don't get that option.

E10 has about 3% less intrinsic energy content than pure gasoline. Pure gas is hard to find, but is great when you can find it.

List of stations here:
http://pure-gas.org/

If you want your emission system to remain functional, you best use the fuel that the manufacturer says to use. My mechanic told me that my O2 sensor failed because of too low octane fuel.

I have made this info into a POI.

So long as this thread is resurecting, let me add some info.

1. Shell at ALL grades is Top Tier; the V-Power is just a little more and hardly worth the price. The ethanol is still there.

2. I have found locally that the PURE gas (90 octane) is Marathon (at a SHell station!) The owner has permission. Although gas prices fly around, that one never changes. It's always $3.559/gal. HOWEVER, being Marathon, it is not Top Tier. So if you want to boost the additives you have to spend a couple more dollars on Techron.

3. Many stations having an option for pure gas in that POI are off-brand stations. Therefore it is a tradeoff in many places.

Alcohol is detrimental to seals on gas powered systems. The government allows it.

Engines are tested with many grades & octane levels, so each motor is calibrated to that. If you want to use a higher grade gas do on a regular bases if you are Concerned with engine cleaner use a higher grade every 5 fill ups. This way you can see if that makes a difference. I have an European car that uses higher octane 98 in Europe but in America the engine was adapted to use 91 octane.

Thank you, it was very interesting, I was always wandering about it.

I think ethanol gas is federally mandated. When you see so-called pure-gas, it is probably racing gas with lead. Not good in modern cars. Good for old hotrods without catalytic converters.

Octane is a measure that qualifies the auto-ignition resistance of the fuel. We want gasoline to BURN completely, from the instant the spark gets the flame going, until the flame expires due to fuel being completely consumed.

What happens with knock (also known as ping, detonation) is that the temperature rise of the unburned fuel in the cylinder reaches a temperature that auto-ignites the remaining air/fuel charge and all of it instantly combusts. There is a huge difference between the normal burn where a flame front propagates away from the spark lug and the air/fuel charges burns, and when the remaining fuel load combusts all at once. That is an explosion and not a burn. Big difference.

The higher octane allows for more advanced ignition timing, compression ratio, boost pressure, etc. and that is where the power comes from. If you can run more advance, you can getter more efficient burns, and make more power. But there is the risk of ping.

Keep in mind that modern cars have knock sensors to detect ping and pull back timing. For that reason I use regular grade fuel. If you want to experience maximum horsepower that is only available at wide-open-throttle, then use high octane to reduce the possibility that the knock sensor and control system will pull timing back.

Pure gas at the station does not have lead in it, but has no ethanol added. Hence, pure gas.

I run my motorcycle on the highest octane I can find. Definitely notice the difference in power from any lower octanes.

agree with you.

The "pure gas" stations near me sell racing gas... no ethanol but leaded.

With my 2000 Honda Odyssey, the manual indicated that there was a 5HP (or maybe it was 7 or 10, not sure now) increase using Premium fuel. Since I had no way of verifying that, I chose not to spend the money.
The electronics would also automatically detect that and retune for the premium, I think based on a knock sensor.

I have read that some cars with premium fuel recommendations will also accept regular and retune, some will not.

Since I no longer have a heavy foot, my little 4 banger is all I need, though sometimes it can't seem to get out of its own way.

If your car does not require the higher octane, don't waste your money. While most newer cars not requiring a higher octane will see a slight increase in mpg with the higher octane, the added cost will more than offset it and it is a loss situation. However, when there was a gas shortage in parts of GA a few years ago, I ran premium just to get that little bit better mileage since I could not depend on when I would be able to get gas again. As soon as it became plentiful again, I went back to the regular stuff.

And that HP increase will only occur at WOT, wide-open-throttle. It will still take 22 hp to propel your car at 65 MPH, not matter what fuel you use.

Then, I imagine it's marked as leaded, as it's the law.

Shell, Chevron, Esso, etc. all sell pure gas here when you buy premium. The only one that doesn't is Husky.

Isn't some degree of ethanol required to be blended into gasoline by Federal Law?

Around here in the northeast, I see signage on the pumps stating that the gasoline contains 10% ethanol.

The only gasoline that is available without ethanol is off-highway, or racing gasoline, and it contains lead.

I can't find any data for on-highway gasoline without ethanol from Shell, Chevron, Esso, etc.

If you put leaded fuel in your car, the catalytic converters are rendered useless.

I doubt Shell, Chevron, Esso, etc. sell on-highway unleaded fuel without ethanol, of any grade. I can't find anything about that on their websites.

If you see "pure-gas" at a station, and the price is exorbitant, it is racing gasoline, and it contains lead.

My 1998 Nissan says premium recommended, when not available, regular can be used.

I ran it 19 years on regular, there is no 02 sensor failure as a result, that's just silly.

The knock sensor did need to be replaced when the car was 15--it threw a code. At this time, I immediately switched to premium, until the sensor was replaced (it's almost a given that one cuts their hand doing this job due to its placement).

I understand this debate will never go away, just like the "should I use synthetic motor oil" and "how do I calculate mpgs" types of threads. But I would say take a step back, and understand what octane measures. It does not measure the "goodness" of the gasoline, rather predetonation.

Was my Nissan harmed by using regular for 19 years? No. Does it produce the 190 HP/ 205 ft. lbs. as spec'd in the brochure, no. Those numbers are produced when using 91 octane.

Here in Canada they do. Regular is 10%, mid-grade is 5%, and premium is 0%.

Truly though, I prefer Spinal Tap brand. It goes to 11.

The thing is, ping is a function of several things.

Weather, temperature, humidity, pressure, load, knock sensor, ignition timing (a biggie), throttle setting, ...

I run regular even though the owners manual says otherwise. Never a fuel related issue in hundreds of thousands of miles, and through several cars.

If it is going to be extremely hot, atmospheric humidity goes up, air density goes down, and the car loses power. The car can be a dog on hills in the extreme heat. So I might treat the car to premium if the weather will be extremely hot. This should allow the control system to advance timing and get a little power back.

I had a 2008 Honda GoldWing 6 cyl. 1800 that clearly stated 87 gas. When traveling through the north western United States I occasionally filled with hig octane 0 ethanol gas. No increase in performance and negligible increase in mileage. The engine is very underdressed, low compression, producing just 120 horsepower.

My 2014 BMW K1600GT is an inline 6 cyl., 10.5:1 compression producing 160 HP from the smaller motor. It clearly states at the filler use 89 minimum. Filling the occasional tank with super (91) did nothing for performance and since I only did it when the price was the same or lower than midgrade didn't cost more.

My BMW K1200GT is an inline 4 cyl., 12:1 compression producing 155 HP from the much smaller motor. Clearly written at the filler, 94 octane required, reduced performance and gas mileage if 91 is used.

With the exception of Shell 91, every 91 gas I've tried runs terrible. Just touching the throttle cause the whole bike to shake unless you're well into the power band. Unfortunately, the reduced performance also means less top end so very difficult to have any fun. Eso 93+ is the best gas I've found but it's almost impossible to find.

Use what the manufacturer tells you. They built and tested it and really should know