All other variables being equal, is it true that a lower...

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Question by EDWARD
Submitted on 8/23/2003
Related FAQ: Gasoline FAQ - Part 4 of 4
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All other variables being equal, is it true that a lower octane level gasoline will have slightly more fuel energy?

Answer by Ryan Goat
Submitted on 11/19/2003
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This is usually not true. A batch of fuel may vary from refinery to refinery and even from day to day, so there is a slight chance that regular gasoline may contain more energy than premium. That being said, energy content is measured in terms of density. Premium gasoline is more dense than regular gasoline, due to the dense additives that raise the octane level. So although it is possible to have more energy in 87 octane than 91 octane, it is very unlikely.

Answer by Eoin
Submitted on 12/27/2003
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This is not true... the additives in gasoline do not increase the energy of fuel by making them more dense. True, a denser fuel (say diesel) has more energy packed into it per unit volume than a less dense fuel. That being said... lower octane fuel ignites easier under heat and pressure than higher octane fuel. The difference lies in the compression ratio of an engine. The higher the compression ratio, the higher the octane needed to prevent pre-ignition. 87 octane may or may not have more energy packed into it than 93 octane, but the 87 will surely provide less power in a high compression engine (9 or more to 1 ratio)

Answer by Nathan
Submitted on 2/17/2004
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Lower octane fuel, by definition, burns faster. This will provide more power, if your engine has a relatively low compression ratio and no knocking.

Answer by tel
Submitted on 2/18/2005
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Generaly the higher the octane rating (or cetane rating for diesel)the more energy is available in a given amount of fuel. Changing from premium 95 RON to 98 RON should give about 2% more power in a modern engine, typically race fuels will be 100 RON or greater.

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