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The PO said he had been using 91 octane and it's at 12k miles. Do you see any risk in me just switching it up to 87?
 

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The manual states 87. TTP recommends 91, I believe, if you are running one of their EFI maps with the respective mods (different pipes, AI/O2 removal, aftermarket air filter, airbox baffle removed, etc).
 

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Been running 87 for years. Often 85. A tank with Seafoam once during the summer and for storage. No valve deposit issues. I imagine a dyno could discern a performance difference but me butt dyno can not.
 

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Depends on how the octane rating is calculated in your area. Here it is (ron+mon)/2. In that case my manual says 89 octane. There's no benefit in using an octane higher than what your engine is designed for because you don't have the compression to utilize the potential energy. Alternatively, using an octane below what's rated for your engine can result in preignition (knock), which can cause engine damage.
 

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I ran 91 for a long time, then switched to 89 without any issues. Though I can't prove it, I think the gas mileage is better with 91, but not enough to justify the expense. I've been forced by circumstance to use 87 a couple times with no ill effects. My bike is not stock.
 

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Depends on how the octane rating is calculated in your area. Here it is (ron+mon)/2. In that case my manual says 89 octane. There's no benefit in using an octane higher than what your engine is designed for because you don't have the compression to utilize the potential energy. Alternatively, using an octane below what's rated for your engine can result in preignition (knock), which can cause engine damage.
Just a side note- higher octane gasoline does not have higher "potential energy". In fact, it's energy content is slightly lower.
 

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Yes that's true. It has less energy per equal volume, but because it can be compressed more, you can get more usable power out of it, but only if you have the compression.
 

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The power/efficiency advantage of higher octane occurs when the engine is equipped with a knock sensor and the ECU adjusts the timing for maximum advance without knocking. Since we don't have a knock sensor on the Bonneville, any gain is lost.
 

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I have a 2012 stock Bonnie and have read all these posts about octane and decided to try it myself. I usually put in 87 and decided to try a tank of 89.
To me, it made absolutely no difference, everything was the same, idle, power, mpg... no difference that I noticed.
So, It's back to 87 for me.
 

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The knock sensor is also used to prevent engine damage. Many modern vehicles designed for 91 octane will actually go into limp mode if sufficient compensation cannot be made, limiting the RPM and speed.
 

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Yes that's true. It has less energy per equal volume, but because it can be compressed more, you can get more usable power out of it, but only if you have the compression.
Then add in ethanol and everything gets goofed up! Argh! :)
 

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I have a 2012 stock Bonnie and have read all these posts about octane and decided to try it myself. I usually put in 87 and decided to try a tank of 89.
To me, it made absolutely no difference, everything was the same, idle, power, mpg... no difference that I noticed.
So, It's back to 87 for me.
Theoretically, you should get more power out of the 87. I would think this would probably only be detectable in drag race along side the identical bike using 89 or on a dyno.
 

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Then add in ethanol and everything gets goofed up! Argh! :)
Ethanol is just ruining our fun - and making food more expensive. 8 dollars a bushel; farmers can't even afford to feed it to their animals anymore. The byproduct they now feed, distillers grains, is resulting in high mortality and lower quality meat.
 

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Ethanol is just ruining our fun - and making food more expensive. 8 dollars a bushel; farmers can't even afford to feed it to their animals anymore. The byproduct they now feed, distillers grains, is resulting in high mortality and lower quality meat.
You know what really burns me up? There are no ethanol free gas stations anywhere near me in Northern Virginia, but riding around through the Midwest this past summer, where they actually grow corn, ethanol free gas was available almost everywhere. In my opinion they ought to be stuck with having to buy that stuff! :)
 

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The Shell V Power here in Ontario is the only ethanol free gasoline. They say ethanol is more renewable, but not when you consider how mush petroleum is used un it's production.
 

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Fuel octane rating has nothing to do with power, it's the resistance to knock. Higher the octane higher the resistance. An engine designed to run on 87 will be just as good as one designed for 91.
Unless you experience knock, using a higher then recommended octane rating gets you nowhere.
 

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Am I reading that wrong? Octane shouldn't have anything to do with how many revs at a set speed. You must have been in a different gear.


Sent from my iPhone using MO Free
 

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Maybe he fitted his bike with a continuously variable transmission. :)

Fuel can't affect a rpm at a given speed in a given gear.
 
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