Fuel additives and fuel octane rating

Modifying and improving: "Petrol, octane and additive tips"

Petrol, octane and additive tips Guide

There is an ever increasing array of fuel on offer. With the addition of a whole plethora of additives the motorist can be left wondering what is the best for his car. Which octane is best and should you use additives? Are all brands of fuel the same?

The quick answer is that all fuels and additives are not the same. We typically buy petrol by its octane rating. The octane rating or RON is solely an indicator of how resistant the fuel is to knock. (Knock is premature ignition caused by pressure within the engine)

In general most Japanese performance cars require a high RON fuel as the Japanese domestic market use a high octane fuel as standard. If you increase the compression in an engine or add a turbo for example you will certainly benefit from the extra RON.

An engine contains a knock sensor and if it detects that knock is occurring it retards the ignition timing of the offending cylinder. If you put a higher octane fuel in your car it is unlikely to cause any damage. Unless the engine is experiencing knock on a lower octane fuel you are unlikely to get any performance benefit either.

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Running an engine which requires high octane fuel on a lower octane will typically cause damage. So avoid going lower than your makers specification. High octane fuel does not mean it is more powerful or that you will get better economy.


High octane fuels in the UK typically range from 97-99 RON. Check with your local forecourt. Try a higher Octane and see if you benefit from it, if you do then this shows that the engine was not operating at peak efficiency under the lower octane.

Race fuels are also available that exceed 99 RON but should only be used in highly modified engines or engines which run high compressions such as Japanese cars and turbo cars.

All petroleum producers put additives in their fuel. These are a carefully controlled blend to enhance both the storage and use of the fuel and maintain the octane levels. Detergents added will help to keep the injectors and engine clean. This in turn means the engine is more efficient and you will get better economy.

Other additives may include bio elements such as esthers or alcohol. We are firmly opposed to the compulsory addition of bio-fuel into our regular petrol. There needs to be more research carried out as early indicators show this to be detrimental to most petrol engines.

Of all the fuel additives we have encountered the only one we can say has made a difference is REDEX. After a long run every car I have used it in shows an improvement of around 2mpg. The older the car the better the improvement.

The octane boosters usually work out more expensive than buying the higher octane fuel in the first place.

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2 Responses to “Petrol, octane and additive tips”

  1. Eva says:

    Hi, thanks for this info, speaks in my favor.. I’m hoping to take my Mazda 3, 2007 from US to Sweden but am concerned with the fuel there being 95 octane. I put 87 in it in the US. In your opinion, would the higher octane damage engine in any way?

  2. admin says:

    Higher octane fuel should do no damage, unlike using too low an octane.

    Bear in mind that the US and Swedish ratings for Octane probably use a different scale anyway so the numbers might be a lot closer than you think.