What is Octane Rating?
At gas stations, you'll see two types of gasoline: "Regular" and "High-Octane."
So, what's the difference between the two?
One major difference is "octane rating."
Simply put, octane rating is an indicator of how resistant gasoline is to abnormal combustion, known as knocking.
The higher the number, the less likely unintended self-ignition will occur even in compressed high-temperature, high-pressure environments, meaning the gasoline has higher resistance to knocking.
A common misconception here is that:
"Higher octane rating = burns better"
"Higher octane rating = more energy"
This way of thinking is incorrect.
Octane rating primarily indicates the gasoline's "resistance to knocking." It is not a direct measure of power output.
What's the difference between high-octane and regular gasoline?
Automotive gasoline in Japan is classified by octane rating according to JIS standards.
Regular gasoline (Grade 2) is specified to have a research octane number (RON) of 89.0 or higher, while high-octane gasoline (Grade 1) is specified to have a RON of 96.0 or higher.
In other words, broadly speaking:
Regular is for general gasoline engines.
High-octane is for engines that require higher knock resistance.
However, the actual octane rating of gasoline sold is not necessarily the same as the minimum value specified by JIS. Specifications may vary by brand and product.
Also, some high-octane gasolines contain detergents, but it's important to check the product specifications of each oil company rather than assuming that all high-octane fuels contain the same additives. ENEOS also explains that the difference between their high-octane and regular gasoline is not just the octane rating but also the inclusion of detergents.
What exactly is knocking?
In a gasoline engine, air and gasoline are typically mixed in the cylinder, compressed, and then ignited by a spark plug.
The flame then spreads, and the engine generates power through combustion at the appropriate timing.
However, if the temperature or pressure in the combustion chamber becomes too high, the air-fuel mixture, which has not yet been reached by the normal flame front, may self-ignite unintentionally.
This can result in rapid pressure fluctuations within the combustion chamber, producing vibrations and sounds often described as a "pinging" or "rattling" noise. This is the phenomenon commonly known as knocking.
Gasoline with a higher octane rating has greater resistance to such self-ignition, making it important for compatibility with engines used in high compression ratio or high-load conditions.
Why do some engines require high-octane fuel?
Engine design dictates varying conditions within the combustion chamber, such as temperature, pressure, ignition timing, and boost pressure.
Especially in engines designed for high performance, a high compression ratio or supercharging can create more severe conditions in the combustion chamber.
Therefore, engine control is sometimes designed with high-octane gasoline, which has high knock resistance, as a premise.
In other words,
Rather than "high-octane for luxury cars,"
It's more accurate to think of it as "high-octane is necessary for that engine's design and control."
What happens if you put regular gasoline in a car designed for high-octane fuel?
This varies by vehicle model, so always check your vehicle's owner's manual for definitive information.
Many modern engines have knock sensors that detect signs of knocking and adjust ignition timing accordingly. Therefore, some vehicles may allow the use of regular gasoline in emergencies.
However, in engines originally designed for high-octane fuel, using regular gasoline may cause the ignition timing to be adjusted, potentially preventing the engine from achieving its intended performance in terms of output and fuel efficiency. Toyota also advises that for some vehicles requiring high-octane fuel, using regular gasoline may lead to knocking or reduced output.
Therefore,
Instead of thinking, "It runs, so regular is fine,"
The basic rule is to use the fuel specified by the manufacturer.
Will putting high-octane fuel in a car designed for regular gasoline make it faster?
Conversely,
Some might wonder, "If I put high-octane fuel in a car designed for regular gasoline, will it increase power?"
However, this is not necessarily the case.
If the engine is designed for regular gasoline, simply increasing the octane rating will not necessarily lead to a clear increase in output unless the engine control system actively utilizes this higher octane to modify ignition timing or boost pressure.
ENEOS also states that there's no problem with using their high-octane fuel in cars designed for regular gasoline, but that's separate from the claim that it will "definitely improve horsepower or fuel efficiency."
What's important is not that
higher octane is always better,
but rather to
use fuel that meets the octane requirements of the engine.
Octane rating and fuel degradation are separate issues
Another common point of confusion is the idea that:
"High-octane fuel can be stored for longer periods, right?"
One of the main differences between high-octane and regular gasoline is knock resistance, but it does not indicate the long-term storability of the gasoline itself.
Gasoline's condition changes during storage due to factors like air, temperature, and moisture. High-octane fuel does not mean it won't degrade. An article from NEXT SCIENCE clearly explains this point.
"For detailed information on long-term storage of gasoline, please refer to 'Does Gasoline Degrade? Changes in Old Gasoline and Precautions for Long-Term Storage.'"
Will adding fuel additives increase octane rating?
This is another point to be careful about.
There are various types of fuel additives.
Some products aim to improve octane rating, while others are designed for cleaning injectors or combustion chambers, improving fuel stability, preventing rust, or focusing on combustion conditions.
Therefore,
"Fuel additive = something that increases octane rating"
is not always true.
If a product does not explicitly state that it has an octane-enhancing function, it should not be considered an octane booster.
NEXT SCIENCE also explains that fuel additives have different purposes, and the approach differs between cleaning products using PEA and products focusing on fuel or combustion conditions.
"For more information on types of fuel additives and their differences from PEA, please see 'What are Fuel Additives? A Clear Explanation of Effects, Types, PEA, How to Use, and How to Choose.'"
Beyond Octane Rating: The Perspective of "Combustion State"
Octane rating is a very important indicator for understanding gasoline.
However, the actual state of an engine is not determined by octane rating alone.
Fuel injection.
Intake air.
Ignition.
Combustion chamber condition.
Engine temperature.
Sensors and electronic control.
Spark plugs.
Injectors.
These various conditions combine to determine the final combustion state.
Therefore,
"The engine feels sluggish lately"
"There's an odd feeling during acceleration"
"The idling is different than before"
Even if you experience these symptoms, you cannot determine the cause based solely on octane rating. For more details, please also refer to "Causes of Poor Engine Acceleration."
Considering Gasoline from the "Combustion" Perspective
When considering regular and high-octane gasoline, the first important thing is to use the correct fuel specified for your vehicle.
Furthermore, when thinking about engine condition, there is also the perspective of:
Not just "what octane is it?"
But also, "how is the fuel currently being used burning within the engine?"
The same applies when choosing fuel additives.
Do you want to change the octane rating?
Do you want to clean the fuel system?
Do you want to consider fuel storability?
Do you want to condition the fuel or combustion state?
The product you choose will vary depending on your objective.
Summary: Octane Rating is an Indicator of "Knock Resistance"
Octane rating is an important indicator of gasoline's knock resistance.
Under Japanese JIS standards, regular gasoline has a research octane number (RON) of 89.0 or higher, and high-octane gasoline has a RON of 96.0 or higher.
However, octane rating is not a direct measure of gasoline's "power."
High-octane fuel for vehicles requiring it.
Manufacturer-specified fuel for vehicles requiring regular.
First and foremost, it is fundamental to use the fuel that the vehicle is designed for.
And when considering engine condition, it is important to take a comprehensive view that includes not only octane rating but also ignition, fuel injection, intake, combustion, friction, and electronic control.
Understanding fuel leads to understanding the engine.
Choose GERHON by fuel type
The current GERHON Fuel Conditioning range has three separate products. Choose the one that matches the fuel you use. For gasoline fuel conditioning, start with the gasoline product below.
-
View GERHON for gasoline
For vehicles and motorcycles that use gasoline. -
View GERHON for diesel
For vehicles, construction machinery, agricultural machinery and generators that use diesel fuel. -
View GERHON for kerosene
For stoves, fan heaters and boilers that use kerosene.
Check compatibility, dosage and precautions on the relevant product page before use. Do not use the kerosene product in boilers without a thermostat.