Is it worth it to pour 98/100 octane gasoline?


"I poured 100 octane gasoline and now my car is going like a blizzard!" - have you ever heard a statement like this? Probably is. And do you believe that high-octane gasoline really has that effect on a car? The story is not black and white, so we have to try to explain it as simply as possible so as not to just add additional confusion.

Misconceptions about octane

First, let's clarify a common misconception - a higher octane number does not tell us that a fuel is "stronger", cleaner or of better quality. It doesn't mean it has a bigger one energy value, so that the car can develop more power.

What is an octane number?

The octane number tells us how much pressure gasoline can withstand before it (uncontrollably) ignites, or "detonates". In other words, an octane number indicates gasoline resistance to self-ignition when the mixture of gasoline and air begins to compress in the cylinder as the piston moves upwards. This mixture must not be ignited "on its own initiative" before the spark plug is thrown.

Can I pour 95 or 98 octane gasoline into a 100 octane car?

You are free. There will be absolutely no problem.

Can I pour 98 octane gasoline into a car that is scheduled for 100 or 95 octane?

You are free. The engine-controlled computer will recognize that you have refueled with less octane than it should and will adjust the engine performance - ie. it will protect it from the auto-ignition of the mixture in the cylinders. In this case, the engine will develop less power and torque.

Why is octane number important?

Because the mixture of gasoline and air in the cylinder must not be ignited before it is spark plug light a spark. Then the mixture starts to burn evenly and push the plunger down. From the spark comes the "front" of combustion, as the designers predicted.

However, if self-ignition occurs, ie detonating combustion before the spark plug throws a spark or at the same time, there are several points from where the "fronts" of combustion spread, so higher pressures and temperatures develop in the cylinder which have various negative effects on all parts. engine.

When the engine is running, specific "clicking", throbbing and similar sounds are usually heard.

Will my car have more power if I pour 98 or 100 octane gasoline on it?

If your car's engine is designed to run on 95-octane gasoline, there will be no increase in power, since, as we explained above, octanes do not indicate the amount of energy in the fuel. However, maybe they will...

Now nothing is clear to me anymore…

The thing is, modern engines are able to adapt to gasoline with different octane values.

So why does a 100 octane gasoline engine develop more power?

Let's take a certain amount of a mixture of air and fuel. The smaller we compress it, the more we will be able to "extract" more kinetic energy by pushing it, which pushes the wheels to turn through the connecting rod, crankshaft and some other "miracles". Physicists and mechanics probably roll their eyes at this definition, but what can we do…

Therefore, engines that have a higher compression ratio (degree of compression) can make better use of fuel energy and develop more power from the same amount of fuel compared to an engine with a lower compression ratio. Of course, not everything is so simple…

What is a compression ratio (or compression ratio)?

Compression ratio or degree of compression - this is the ratio of volume (free space) in the cylinder when the piston is at the lowest point (lower dead center) and when it is at the highest point (upper dead center). The higher the compression ratio, the more useful energy the engine can extract from the fuel - so to speak…


Will my car have more power if I fill up with 98 or 100 octane gasoline?

Modern engines can adapt to different octane values ​​of gasoline. Depending on the type of engine, ie how the valve control system, injection and ignition is constructed, as well as the ability of the computer to control the operation of the engine based on various parameters depending on the driving mode and octane value of fuel, a certain engine will be able to get more power from high-octane gasoline.

It seems complicated and it is complicated. It is impossible to say without measuring on the dynamometer how much power a certain car will develop with 95 octane gasoline, and how much with 98 and 100 octane gasoline.

This is compounded by the fact that some experts say that the engine needs to run on high-octane gasoline longer in order for the computer to become fully accustomed to it, and only then can that particular engine, based on its own capabilities, derive maximum potential from high-octane gasoline.

By the same token, if a modern 100-octane engine is filled with 95 gasoline, the computer that controls the engine will adjust its operation to protect the engine, but this will result in a drop in power and torque.

How does the engine adapt to different octane fuel values?

Since high-octane gasoline is more resistant to self-ignition (detonation), it provides the possibility of later spark ignition, ie achieving higher pressure (or compression - not compression ratio / degree, since these are two different things).

Spark plug
Spark plug

Thus, since a higher pressure is achieved in the cylinder before the fuel ignites, more efficient fuel utilization occurs.

Namely, let's say that in theory, a spark plug should throw a spark when the piston reaches the top dead center, ie when it stops and should move downwards, so that the ignited mixture of fuel and air pushes the piston with all its force. However, in practice, the mixture cannot burn instantly - the spark plug ignites the mixture in its immediate vicinity, and then the combustion front spreads from there, with an increase in pressure and temperature. Since the piston is moving at high speed, while that combustion would reach a sufficient force, the piston would already "run away" down.

That is why the ignition system is adjusted so that the spark plug throws a spark before the piston reaches the top dead center. The moment of throwing the spark should be precisely determined so that the mixture burns completely, the maximum pressure is obtained which will push the piston down and at the same time avoid various negative effects.

At lower rpm the displacement of the firing angle is smaller, while at higher rpm it is greater. Otherwise, since this is a circular motion, the timing of the ignition moment, or as we call it ignition, is expressed in degrees of crankshaft rotation angles (crankshaft or ignition timing axle). So we use the term ignition angle.

The optimal ignition angle is different for petrol of different octane number, but it also depends on the engine operating mode and load. Therefore, the moment in which the spark will appear on the spark plug, ie the ignition angle, should be changed in accordance with the current conditions.

We will not go into which regimes are better for earlier pre-ignition, and for which later. We just want to have the optimal ignition timing of the mixture in the cylinder, in order to make the most efficient use of the energy of controlled combustion of that mixture, without excessive pressure or temperature accelerating wear and tear or damage to various engine parts.

Of course, the efficiency of gasoline energy utilization depends on many other factors, including the basic engine design (shape of the combustion chamber and piston head, position of the spark plug in the chamber, the ratio of width and height of the cylinder volume, number of valves,), valve control system upravljanja Depending on the engine manufacturer, there are indeed numerous variations on this theme.

Modern engines have sensors that register the occurrence of detonations. They send this information to the computer, which therefore changes the ignition angle. So, if the sensor starts to detect detonations, the moment when the mixture ignites will change in order to prevent detonation, ie self-ignition of the fuel.

Otherwise, the computer tries to constantly keep the engine on the verge of detonation in order to extract as much power (energy). Therefore, when high-octane fuel is refilled, the danger of detonation is significantly lower, so the computer will adapt to that fuel, ie change the pre-ignition angle (the moment of throwing the spark).

Is high octane fuel of better quality?

Many drivers are confused by the fact that high-octane gasoline is usually advertised as a higher quality additive fuel, which brings better performance and lower consumption, so drivers often have unrealistic expectations. In short - high-octane gasoline may or may not be of better quality in terms of lower content of various unwanted substances in it, as well as the presence of additives that have various positive effects on the engine.


Neither do the car use instructions (or are they?)

Take for example the 10 Hyundai i2008. His instructions say that unleaded gasoline with an octane value of 95 or more octane should be used. So, 95 is the minimum, and the owner is free to pour 98 or 100 octane gasoline.

However, it also says that unleaded gasoline with an octane value of 91 to 94 octane can be used, but that this will have a negative impact on engine performance. Nowhere is it specified whether and to what extent the improvement will bring high-octane gasoline, nor how much gasoline with less than 95 octane will affect the reduction of power or torque.

Does 98 or 100 octane gasoline reduce fuel consumption?

Some drivers swear they have reduced their consumption after starting using 100-octane gasoline, but just as with power and torque, no conclusion can be drawn until serious testing has been completed.

What do high-octane fuel sellers say?

One of the domestic pump chains says that their 100-octane gasoline has active components that ensure more efficient operation of the engine, improve its performance and make it more durable. An increase in engine power of up to 7%, up to 10% more powerful acceleration at high speeds and an increase in torque of up to 5% are reported.

Others only report the same or similar positive effects, but without percentages or other data.

High-octane gasoline also helps older-generation engines under certain conditions

The possibility of detonations is higher when the engine is at low revs and the driver presses the accelerator pedal harder. In such a situation, the advantage of 100 octane gasoline over 95 octane can be noticed. Of course, you should never accelerate sharply from low revs when we are in a higher gear, but the fact is that many drivers do that.

Perhaps such drivers, since they notice that high-octane fuel "erases" the consequences of their wrong driving style, although they are not aware of it at all, mostly claim that they immediately noticed a big difference in engine power when using 100 octane gasoline.

The situation is similar when the car is heavily loaded, going uphill or towing a trailer, and if it is a weaker atmospheric gasoline whose owner is not aware that he simply has to chase it at higher speeds, here is the perfect scenario for detonations in the engine. They are manifested by characteristic clicking / tapping, which is often said to knock valves.

An older engine that has some problems in operation can also react positively to gasoline with a higher octane number. However, the use of high-octane gasoline is not the solution in that case.


If your car has an older generation engine, there is no need to buy high-octane fuel. With more modern vehicles, there is no general answer as to whether it pays to use 98 or 100 octane gasoline. Some engines will be able to feel improvement in all operating conditions, some only when the car is very loaded and / or at a very low speed, and some owners will not feel any difference compared to 95 octane gasoline.

A special story is the additives that are added to high-octane gasoline by unwritten rule, as they can, over time, in some heavy-duty engines made in harsh urban conditions, can over time remove deposits from various components and thus "engine" lubrication.

Author: Dragan Romcevic

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