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All of that boils down to these points.

The optimum moment for combustion to be at full force is 11-14* ATDC. Spark usually happens 10-30* BTDC. Obviously, the burn rate of the fuel and your total timing advnace and more importantly (since it isn't adjustable) your compression ratio will determine what octane fuel your engine needs.

Timing in most modern motorcycles is based of a static table. You can't adjust it, the same as you can't adjust the timing in your late model car without computer modifications. Given the same timing, compression, and other variables, lower octane fuel will give you more power. Just remember that you can't always hear detonation (pinging). My car has knock sensors so the engine doesn't grenade from knock (pinging, whatever) before I finally hear it. Just because you don't hear it, or feel it doesn't mean it isn't happening.

Lower octane fuels ignite at lower temperatures. If you develop a hot spot in the engine, higher octane fuel is more likely to not pre-ignite (different from detonation) and ruin your engine VERY fast.

Most sportbikes do actually require 90 octane or higher as that is often the highest octane available California.
 

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Interesting read, I just may try and run the different fuels and see how my bike reacts. If I had a bike with 12:1 compression I don't think I'd want to try it out though.
 

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I have read for years that using a higher octane than the manufacturer recommends is a waste of money and could actually get you less power due to the fuel burning slower/less efficiently. This pretty much confirms it.

However, I had read that the addition of ethanol in gas was to absorb the moisture in your fuel tank to help prevent icing in the winter and rusting. Water doesn't mix with gas, so condensation would build up in your tank (or the tank at the station).

I'm not yet ready to get away from gas with up to 10% ethanol. I'm fairly sure that the manufacturers take into account the useage of ethanol in fuels and design the fuel systems accordingly (those with older carburated bikes may wish to consider this) due to alcohol's corrosivity of some metals.
 

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Higher octane gas doesn't give your bike more HP nor does it burn "cleaner". It just burns slower. If the manufacturer doesn't recommend high octane gas for your bike, then you're just wasting money by using it. The exception to this is if you notice pinging or knocking when using lower octane gas... in those cases they recommend going with a higher octane gas.
 

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That's a good find, I may try at least going down from 93 octane to 89 octane. Not sure if I want to rish regular unleaded though. I use 89 for the truck, it seems to work fine on the cage, we'll try and see if there's a difference on the bike.
 

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Huh... I thought this would be some quack, quasi-science article... but I put a lot of stock in what Motorcycle Performance has to say. I'll try switching.
 

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Ozy said:
Damn, the lowest octane we have over here is 95, and i have always used 98...
Over here our gases use an average of Research and Motor methods for octane rating. I believe yours use only the higher of the two, so they'll be higher numbers for the same detonation resistance.
 

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I think my bike only requires 85... I wonder how much power can be gained by tuning for 93 :)
 

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Check Your Owners Manual Before Switching!!!!!
 

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MustGoFast said:
I think my bike only requires 85... I wonder how much power can be gained by tuning for 93 :)
(talking mostly out my ass...) You'd get most of the boost by upping compression ratio. You'd probably be able to get quite a bit, but I think you'd need to do quite a bit of work - more than decking the heads and a thin gasket. But then, I'm not an engine builder, I don't play one on TV, and I didn't even sleep in a holiday inn express.
 

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Dan you are on the right track though. Actually just decking the heads with a thinner gasket might be all it takes to require it. Remember that the combustion chambers on sport bike motors are not all that large. I think you could jump the comp ratio by a half point very quickly. The other thing you could do is advance ignition time. Though how much you could get before performance suffers I do not know. When it is all said and done, is it really worth going through the work just so you could justify higher octane fuel?
 

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Only if it makes the difference between earning contingency $ and not...

Even then, you'd probably get a quicker advantage from tuning for an oxygenated race fuel. Although over a season, that would probably be more expensive than a supersport build (which shouldn't require rebuilds all that often).

'Course, if it just turns your crank (ark ark) to get a bit of power through an engine build, who am I to stop you?
 

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In my experience with cars you can actually run leaner on higher octane fuel w/ out risk of detonation and the leaner run allowed a better HP output. So I may be able to pick up HP by simply leaning it out in w/ the PC on a dyno.. but who knows.
 

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My 2002 DR650se liked low octane gas... my 2006 KTM950sm likes 91 Octane. Stalled on Petro-Canada 94... not sure if that was just a bad batch of gas, but won't bother trying anything else then that manual recommended 91
 
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