Octane Number 101

by Stefano Nicola

Urban myth : “a humorous or horrific story or piece of information circulated as though true, especially one purporting to involve someone vaguely related or known to the teller”.

Well, if Google says so, who are we to say otherwise ?

Today my goal is to discuss an Urban myth, which, interestingly enough, is somewhat humorous and horrific at the same time : Fuel’s Octane rating.

That’s right ! That mysterious number you read when you pump some fuel in your car. The same number that, inexplicably, seems to drive up the price of fuel sky high!

What seems interesting is that most gas companies advertise higher octane rating fuel as “Premium”, “Clean”, sometimes even "Super Clean" - almost to suggest that the higher the rating the better the product you are buying is ! But what does that really mean ? Is the combustion process actually clean ? Does it make your car faster ? What does this number really do for you?

Well, let’s put it this way; this whole octane number deal is very much related to the vehicle you drive. To debunk part of the myth - it doesn’t really burn “cleaner” per say, some higher octane fuels, however, contain additives to prevent your car injectors (the devices that “spray” the air-fuel mixture in your engine’s cylinders) from getting covered in gunk (mostly carbon based).

But going back to this number - to put it simply, the Octane rating indicates the resistance of a particular fuel to “auto-ignition”, that’s right ! The higher the octane number, the harder It is to burn that fuel. Not exactly what you thought, is it ?

Most people seem to think that a higher number means that the gasoline they picked burns … faster ?

What it really does, is burn “better”, but let’s take it one step at a time.

As you probably know, the temperature in a car engine is pretty high (actually very high :199-220 degrees Fahrenheit on average), as engines get older, or are modified to deliver more power, the temperature increases further. Now, most engines are designed to “burn” the fuel at a very specific point in time. This relates to what is generally known as “engine cycle”. IF the explosion in each cylinder, which is what generates power and makes the car move, does not happen by design, the power output is affected and there is a good chance that you’ll experience what is known as “misfiring.”

Fuel Cap.jpg

Misfiring can cause several issues including unburnt fuel to exit through the exhaust. Why ? Well, when misfiring happens, the combustion within the engine does not have enough time to happen properly - thus some fuel isn't burnt and that same fuel is sent through the exhaust.

The thing is, not all cars need a high octane number; but don’t just take my word for it. Most auto manufacturers list a “suggested” rating on the fuel tank door and in your instruction manual.

Using fuel with a 95 rating on an average vehicle is as useful as building a pool on your house’s roof - expensive, and all in all, pretty useless. It won’t make your car any faster and it won’t be any “cleaner”, it’s simply not needed, and (unfortunately) it won’t be of any benefit to the environment either. So, before you choose the most expensive fuel out there, check your instruction manual.

It might just save you some money !