Originally Posted by mattmy99

The octane number of a fuel is measured and is defined by comparison with the mixture of iso-octane (trimethylpentane) and heptane which would have the same anti-knocking capacity as the fuel being tested. The percentage, by volume, of iso-octane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. This does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties.
Fuel with a RON of higher than 100 are possible because iso-octane is not the most knock-resistant substance available.

So in theory, a fuel with with RON98 properties is exactly that, RON98. However, they all contain different ingredients to achieve that rating. All of which perform differently in different engine.

I personally have had the most success using BP ultimate.