High Octane Myths – What Does That Number at the Pump Really Mean?
The truth about Regular, Plus and Super gasoline.


In the automotive world, there are many common myths, which are repeated so many times that, after a while, they eventually transform themselves into ‘facts.’ Unsurprisingly, many of these ‘facts’ have to do with gasoline, whether they be regarding fuel mileage, power possibilities or some other arcane aspect of the internal combustion engine. Gasoline can be a confusing topic, and it is easy to make assumptions about it that may seem logical, but which on closer examination, turn out not to be true. A perfect example of this practice can be seen with octane ratings.

What are octane ratings? Simply put, when you pull into the gas station and are presented with the array of different fuel grades that you can pump into your car, the numbers written above each button or nozzle indicate that particular grade’s octane rating. Typically, the range will run from 87 octane on up to 93 octane.

In the world of automobiles, it is tempting to associate higher numbers with higher quality. After all, more horsepower and more kilometres per litre are a better thing, which feeds into our perception that more impressive octane ratings also equal higher performance. Gasoline companies understand this mentality and do nothing to dissuade drivers from it, labeling 87 octane gas ‘Regular,’ and 91 or 93 octane ‘Super’ in an attempt to reinforce this way of thinking. After all, since ‘Super’ is priced higher than ‘Regular,’ it’s in their best interest to convince as many people as they can that paying a bit extra means getting better quality gas.

Unfortunately, this is where the myth of what gasoline’s octane rating really means creeps into the picture. Time and again, people will be told that high octane fuel burns cleaner or more completely, and that it will give them extra power and better fuel mileage than Regular octane gasoline because it contains more ‘energy.’ These blanket statements are simply not true. In fact, the octane rating for gasoline has nothing to do with the amount of power locked inside of it – it actually relates to just how much a fuel can be compressed before igniting. The higher the number, the less likely it is to ignite under pressure.

Why would anyone want to produce a fuel that was actually harder to ignite once inside an engine? To understand the role that octane ratings and ignition pressures play in a motor, it helps to be familiar with the term ‘knock.’ Essentially, when gasoline is sprayed into a cylinder by a fuel injector and mixed with oxygen, engine designers expect it to remain there in vapor form until it is time for the sparkplug to light it up, causing the explosion that drives the piston down to generate horsepower. The timing of this explosion is critical, as gasoline that ignites too early causes ‘knock,’ which reduces engine output and efficiency and which, in worst-case scenarios, can actually physically damage an engine.

In most engines, knock is rarely an issue because the compression ratio – that is, the pressure that the air/fuel mixture is put under in the cylinder – is low enough that Regular gasoline’s octane rating is sufficient. There is absolutely no benefit to running Premium fuel in a standard motor, since it will never be able to take advantage of that gasoline’s higher knock resistance. However, more aggressive engine management schemes, especially those found in turbocharged or supercharged vehicles, can turn up the compression to a high level, requiring much higher octane gasoline to avoid knock.

How can you know whether your car actually requires Super gasoline or whether it can get by on Regular? Almost every vehicle will list the octane rating necessary to run it safely inside the owner’s manual. Some luxury or sportscars might even place a small reminder on the gas gauge itself stating ‘Premium Unleaded fuel only’ to make sure you don’t forget.

To wrap things up: no, you won’t see a power or fuel efficiency increase by running high octane fuel in an engine that has been tuned and designed for Regular gas, nor will doing so perform any extra ‘cleaning’ inside the motor. On the flip side, running low octane fuel in an engine built for Premium can increase the risk of engine damage and will certainly impact that unit’s overall performance. The next time someone tries to pass these myths off on you, you can try explaining to them how octane ratings really work – or you can just smile and nod, pay for your gas and move on.

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Great article on gasoline and the myths surrounding it. It should be made very clear if the manufacture recommends using premium fuel that's what you should be using, that's not a myth! I would never consider damaging my engine to save 10 cents a gallon or even more. If you can't afford the premium fuel you can't afford the Infiniti/Nissan!
Gary

 

Yep...plain and simple!
Put in what we are told and our engines will love us in return.
Unfortunately, for us up here, the difference is often 10 cents a Litre more but that's still no excuse to pump regular.

 

beauty of Osiris... aggressive tune that require higher octane and econo tune that allows for low octane... That's actually were the term "econo" came from - its what a few of us at Churches called it when you can run the cheaper fuel... as it turned out a couple tests were done to determine that even with same octane the mpg was little better.

Anyway - most tunes (including TS) will require higher octane...

FWIW.

 

If you actually read the article, is states that you should follow the manufacturer recommendation. And that cars built to run on regular fuel will not BENEFIT from premium.

So what is the point of this article in a G35 forum? An excuse to run "regular" on a G35 because you didn't read the article but just the title?

 

jibber -
There is nothing in the title that infers running regular fuel in a vehicle in which premium fuel is recommended.
And yes, if you read the article you can summarize, the car engine will run at maximum designed performance but putting in a lower octane will be detrimental and putting in higher grade will not be beneficial.
The point of posting the article was to explain why. I have seen a lot of questions raised like..."is it ok to run regular when it says premium"? or "Will my car run better, go faster, get better milage, if I use 94 octane"?
I just thought it was an interesting article, well written in layman's terms so I posted it on this, a PUBLIC, forum.

 

Here's another good read.

 

Yes great, that's on page 9-3 of my manual too. Most people never take the owners manual out of the compartment. We are not here to judge and criticize them.
Where does the owners manual explain WHY you should ONLY use recommended fuel, such as the article I posted and the reason for this post?
What's next? Are you going to tell me we shouldn't ask why?
I didn't start this thread to debate over whether or not its safe to use variable octane fuels in our (or any) cars. I think you may have misunderstood the intention.

 

I've always run 93 octane in all my cars, regardless. Even if it's just a myth that it may or may not be better for the engine, for a 2-8 dollar total price difference on a fill-up, I'd rather pay extra and not take a risk of damaging the motor.
If you can afford the car, you can afford the gas to put in it.

That's just my way of thinking it.

 

All I said was here is another good read. No need to get your panties in a bunch.

 

^+1

Its not that much difference anyways

 

Great article Paul, thanks for posting

the manual says 91 is best for my ride, so thats what I use.

 

I thought it was a good article. I get so sick of people's complete ignorance around something so simple.

Also, for those who put premium in even when it's not needed, it adds up after a while. Where I live premium is usually $.20/gallon more than regular. Assuming you fill up 18 gallons, three times a month...that's almost $150 a year. It's not all that much money in the big scheme of things, but you might as well have just flushed it down the toilet.

 

+1, I agree, I wish our premium was that cheap, like I said we pay 10 cents/litre more than regular

 

Yeah, that would definitely add up. Most other places I've been are usually between $.25 and $.30 cents more per gallon.