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Old 05-01-2013, 06:29 AM   #16
anotherguy
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All my bikes require higher octane fuel. The off roaders get fed Sunoco EXO2 which is 107 R+M/2 octane. Used to use VP but they've made it so difficult for their dealers it became hard to find consistently. The street bikes enjoy premium (91+) from Top Tier stations whenever possible.
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Old 05-01-2013, 06:54 AM   #17
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Originally Posted by RedWolf View Post
Burning something with a higher rating than the engineer designed the motor to

The Engineer tuned for. You can usually tune to run higher octane, you just have to account for the slower burn with the ignition advance. That being said, yes higher than the recommended octane level just contributes to valve/piston deposits.


The octane requirement also decreases with altitude, I could run my Speed Triple that is tuned for only 91 on 86 at 9000 feet without pinging.
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Old 05-01-2013, 08:10 AM   #18
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i get better mpg using prem. fuel

i get a couple more mpg using regular automotive grade fuel with the highest AKI rating. (93 octane)..
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Old 05-01-2013, 09:00 AM   #19
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Originally Posted by Tripped1 View Post
The Engineer tuned for. You can usually tune to run higher octane, you just have to account for the slower burn with the ignition advance.
I have never met an engineer who has tuned an engine so it can run higher octane gasoline. People tune engines for more power. Mods used to get more power make the engine more likely to detonate. Higher octane gas is more resistant to detonation, so it gets used. Higher octane gasoline does not add any power on it's own. Tuning dictates the octane rating, not the other way around. Along those lines, timing isn't changed to allow the use of higher octane gas, higher octane gas might be used to allow changing the timing.

Which leads to; higher octane gasoline does not control detonation by burning slower than lower octane gas. Slowing down the burn would make detonation even worse. Swirl is put into the intake charge to make the mixture burn faster. Dual plugs cause the mixture to burn faster. Burning the mixture faster is a good thing.

At a given temp and given pressure as seen in an engine, you've got a finite amount of time before the mixture goes bang with no help from a flame front. Call it the delay period. The mixture has to burn fast enough that there's nothing left to explode when the delay period runs out. (Unless of course you're running a diesel, in which case you want to exploit this compression ignition stuff)

Raising compression shortens this delay period, leading to issues with detonation. To avoid this, you need to burn the mixture faster or make the delay period longer. The mixture can be made to burn faster by adding another plug. Or by adding swirl to the mix, exposing the flame front to the mixture faster than just letting it burn on it's own. The delay period can be made longer by raising the octane, or by lowering the temperature. Any combination of these things (and more) help avoid detonation caused by higher compression. Point being that lowering flame speed goes counter to other mods that are done.

Slowing down the burn to avoid detonation makes no sense, detonation is not a result of the flame front moving too quickly, it's the result of the mixture being exposed to high temp and pressure for too long so it explodes. Burning quickly is good. Exploding is bad. Flame fronts do not speed up to the point of an explosion.
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Old 05-01-2013, 09:15 AM   #20
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The owner's manual says 87 octane, so I use 87 octane. I figure the engineers with doctorates at Yamaha are way smarter than me.
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Old 05-01-2013, 09:27 AM   #21
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I've never been a fan of running a higher octane than necessary. Sure, I've had engines that would call for it. Those got the higher octane. But a ho-hum engine would do just fine on ho-hum gas.

Then came ethanol. Darn it, this stuff sure changed things.

The ethanol blended gasolines degrade themselves at a remarkable rate. Not a big deal in the cars, where I go through lots of gas and refill every few days. But very much a big deal in the gas can, and in the carburetors and tanks of things that sit. It goes from a good combustable mixture to a poor burning fuel in just a few weeks. I've seen it become absolutely incombustable in just a few winter months.

The ethanol blended gasolines separate. Again, not a big deal in the car with lots of turn over, but a huge deal in gas cans and the fuel tanks of sitting gravity fed things. More than once I've found equipment not running because water was coming out of the tank, not fuel.

The ethanol blended gasolines are leaner. Again, not a big deal in the cars, or fuel injected engines. But 2-strokes, oye is this a problem!

I have found the higher octane ethanol blended gasolines seem to hold combustability longer, and it seems to help compensate for the leanness created by the ethanol.

So, using higher octane gasoline in my chainsaws, my lawn mowers, and my motorcycles gives me engines that start more easily, run a bit better, and in the case of some, produce more power (chainsaws are a good example).

So, for an added cost of about $20-40 a year, I chose to generally run higher octane fuels on those engines.
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Old 05-01-2013, 10:38 AM   #22
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Running higher octane gas than what the owner's manual is just a waste of money, and causes deposits to form in the engine.

An engine rated for 87 octane will make LESS power on higher octane gas.
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Old 05-01-2013, 12:01 PM   #23
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Quote:
Originally Posted by DesmoDog View Post
I have never met an engineer who has tuned an engine so it can run higher octane gasoline. People tune engines for more power. Mods used to get more power make the engine more likely to detonate. Higher octane gas is more resistant to detonation, so it gets used. Higher octane gasoline does not add any power on it's own. Tuning dictates the octane rating, not the other way around. Along those lines, timing isn't changed to allow the use of higher octane gas, higher octane gas might be used to allow changing the timing.
So you are saying that there is never any play that you can crank in advance and add fuel and get more power?

Really?

That is what I mean by tuning for higher fuel, yes, the mechanical events certainly dictate the minimum, there is almost always room to get a little more boom with tuning, if you are willing to go premium only.
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Old 05-01-2013, 12:56 PM   #24
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Originally Posted by Tripped1 View Post
So you are saying that there is never any play that you can crank in advance and add fuel and get more power?

Really?
Looked to me like he said he never saw them build an engine in order to run high octane fuel, but instead built an engine that needed to run high octane fuel.
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Old 05-01-2013, 08:51 PM   #25
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Originally Posted by BikeMan View Post
i get a couple more mpg using regular automotive grade fuel with the highest AKI rating. (93 octane)..
Enough more to justify the extra fuel cost? Likely not.
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Old 05-01-2013, 08:53 PM   #26
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I'm pretty sure that the only factors that determine what octane your engine needs is the compression ratio, and the material that the engine is made from.
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Old 05-01-2013, 08:58 PM   #27
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Quote:
Originally Posted by Tripped1 View Post
So you are saying that there is never any play that you can crank in advance and add fuel and get more power?
.
I'm not saying anything of the sort, and don't understand how you get that from what you quoted.
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Old 05-01-2013, 09:43 PM   #28
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I'm not saying anything of the sort, and don't understand how you get that from what you quoted.

Well that was what I was saying. Perhaps I wasn't very clear about it.
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Old 05-01-2013, 10:47 PM   #29
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Originally Posted by k-moe View Post
I'm pretty sure that the only factors that determine what octane your engine needs is the compression ratio, and the material that the engine is made from.
Basically, yes.

But, there are other factors. Some of which have been mentioned on this thread. Ignition curves, total advance, fuel delivery, gearing, weight of vehicle, cam lift and duration, etc etc.

But, for a bike in factory tune, run what the manufacturer recommends. Period.
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Old 05-02-2013, 06:02 AM   #30
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Well that was what I was saying. Perhaps I wasn't very clear about it.
Oh.... In that case, nevermind.
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