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When I first got my 1100classic, I was going by the common wisdom of filling it with 91 unleaded on the advice of a couple of people, not thinking about it much. However I recently read on PCS that the stock engine works best with 87. Is this the case, and what difference does it really make? And is it a problem to mix fuel grades in the tank?
 

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octane in pump gas only determines how easily the fuel reaches combustion, it has nothing to do with how much energy it produces or how efficient the fuel is when it burns.

Generally an engine develops the most horsepower using the lowest octane fuel that will not cause detonation. Unless you have made changes to the engine (other than intake and exhaust) you should go with what the owners manual says.

Mixing doesn't hurt anything provided the mix doesn't make the overall octane too low for the engine. So it can only be an issue on engines that require higher octane.
 

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+1 on the answer and I would add. At 8.3:1 the compression in not high enough ping and or detonate with 87 Octane. At 10.6:1 as with the PCS High Compression Pistons you'd need 91 Octane and with SS Customs 11.1:1 HCPs you'd need 93 Octane. Due in both cases increased above 185psi or more cylinder pressure.
 

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This is unreal! I can't believe there is not one comment about how the higher (priced) octane fuel will give you 20% more power and gains of at least 10 mpg!

Right on, all! Use what the manual says, and use the money you save from buying the un-needed high octane fuel on more important stuff. Like chrome!
 

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Fuel

The 1100 has an 8,3 to 1 compression ratio. does not have an oxygen sensor and fuel injestion. It cannot make changes to alow for higher octane gas.

You may well see a differance on a 1300 with its 9.5 to 1 and electronic fuel control.

Dave
 

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Allow for Higher octane? The 950 is to use 87 octane per manual, same for the 1100. It's the other way around. Higher octane is just a waste of money. If you had higher compression your engine computer might be able to retard the timing to use lower octane fuel. Depending of course on programming limits. Your computer can't raise the compression of your engine. Your compression ratio determines the octane needed. Most high compression engines really don't like the "discount" stuff. LOL
 
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