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Difference Between 87 and 91 Octane Gas

87 vs 91 Octane Gas

When it comes to gas, you can choose between a lower octane gas or opt for a higher octane rating. Two common octane ratings are 87 and 91. The main difference between 87 and 91 octane gas is just the additive that they add to it. They are still the same unleaded gasoline that will work on your car.

The purpose of the additive is to make the gas more resistant to pre-detonation, more commonly known as pinging or knocking. This happens because the gas can only be compressed so much before it becomes hot enough to ignite on its own without a spark from the sparkplug. The effects of pre-detonation may not be automatically felt, but prolonged occurrence can destroy the engine. It is fairly easy to detect though as it has a characteristic ping or knock sound that is not present when the engine is functioning properly.

An 87 octane gas is more prone to pre-detonation since it ignites at a lower temperature than 91 octane gas. If your engine is experiencing pre-detonation when using 87 octane gas, you may try switching to 91 octane gas to see if the problem gets resolved.

Another difference between 87 and 91 octane is the amount of power that they deliver. Because 91 octane gas does not detonate as easily, it can be compressed more than 87 octane gas. Being compressed more results in more forceful explosions that give translate to more engine torque.  But changing to 91 octane gas doesn’t automatically mean that your engine would perform better. It is still dependent on the design of the engine. Remember that the timing of the sparkplug determines when the fuel ignites. So if the engine is designed for a certain compression setting, then the engine will not compress the gas more than that.

When choosing the right gas for your vehicle, the best thing to do is to look at your user manual. If it suggests using 87 octane or 91 octane gas, then you should follow it. Using a lower octane rating creates problems with the engine. Using a higher octane rating, while it may not cause adverse effects to the engine, means that you are spending more for no reason.


  1. 87 and 91 octane gas uses different kinds of additives
  2. 91 octane gas doesn’t detonate as easily as 87 octane gas
  3. 87 octane gas is more prone to knocking than 91 octane gas
  4. 91 octane gas can deliver more power than 87 octane gas

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  1. Lovely now i understand i can use 91 in my Sentra SL, my car gives me lot more performence then 87. Owner manuel says use
    Atlest 87 octan ( research 91). i was too confused.

    • Mr Sulaiman
      Well no, it does not give you more power, unless you changed the compression as the article describes. Too many think putting in 95 instead of their model’s recommended 91 means more power, it just means more money as also described here.

      • Ok I think your manual is showing you to use 87 octane Anti-Knock Index (AKI), which is equivalent to 91 Research Octane Number (RON) used elsewhere in the world. In other words, your minimum would always be 91 ron fuel, but no advantage using 95 or higher.

  2. How to change Mobile number..

  3. I know that the octane number is a rating, but if you were to mix equal parts of 87octane and 91 octane fuel, what would the octane rating be?
    89 would seem logical, but i know that’s not the answer.

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