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post #1 of 9 (permalink) Old 11-11-2007, 07:46 AM Thread Starter
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Better gas?

This may be an common knowledge to most of you. If you use higher grade gas in your bike, does it perform better? Ive been riding on and off for a year now. I never noticed a difference in my car when I use a higher grade, but I have in my bike recently. I had previously used regular unleaded gas (87) until a week ago when I threw some high grade in there (93). Once I used it, i noticed my bike performed better, sounded better, smoother acceleration and more.

My question, is this common with all sportbikes? I have a PCIII installed so is the change even more obvious because of that? I just want to understand the mechanics a little better
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post #2 of 9 (permalink) Old 11-11-2007, 08:10 AM
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1st, its all depends on what the bike manufacturer recomends.
2nd, with a pc3, it depends on what the map is tuned for. reguardless if its a custom map or one from some where else (ex. someone elses map, dyno-jets map from their website.

i run premium only in my bike. if i can find 94, i run that, otherwise its 93 (mostly the only premium grade locally). fasterbusa runs cheap grade fuel in his busa, but thats what the busa recommends.


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post #3 of 9 (permalink) Old 11-11-2007, 08:59 AM
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ya, i just use which ever gas my bike likes. with the regular stuff (86-87) i get some ticking but it will go away with the mid-grade. so mid grade it is.
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post #4 of 9 (permalink) Old 11-12-2007, 05:49 AM
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The lower octane gas has more energy than higher octane, but higher octane cools the cylinder more than low octane gas. If the cylinders get too hot, you risk pre ignition/detonation, which either sounds like a tapping/knocking noise, or in worst case scenario, like your engine is trying to fall apart. In either case you are looking at some engine damage. As long as there is no knock, you want to go with the lowest octane rating the bike will run smoothly with, since you'll get more power out of it. Anything higher than what the enigne needs is a waste. PC3 controls ignition timing (I think) which has an effect on what octane the engine needs to run smoothly. Maps ussually extract more power by advancing ignition a touch, taking advantage of higher grade gasoline.

Some cars have anti knock sensors, and the ability to advance/retard timing. These vehicle will take advantage of higher grade gas to advance the timing and provide more power/better milage. If the car does no have these features, than anything over regular is a complete waste.

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post #5 of 9 (permalink) Old 11-12-2007, 08:35 AM
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Well...........................sort of. Octane rating relates to the ability to avoid detonation and knocking. The energy content isn't really any different (at least not significantly) between octane grades, but high octane gas does burn slower, so it will not be as efficient in an engine that can use a lower octane.

Generally, using a higher octane gas than is required will result in a reduction of power, and an increased potential for fouling. A point or two isn't going to make a difference, but if you run 110 octane race fuel in a stock engine, you're going to foul your plugs and measurably reduce your power. What the 110 octane does for you, is to allow you to use a higher than stock compression (and to some degree, more advanced ignition timing) without destroying your engine.

In terms of engine safety, there is a minimum octane that you need to avoid detonation. In terms of engine performance and life, there is an optimum octane - which is the minimum required for your engine.
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post #6 of 9 (permalink) Old 11-12-2007, 08:57 AM
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Higher octane fuel is richer in light alcohols (methanol, ethanol and such) which have less btu's/liter. By itself, this would hardly have a noticable effect. However, these substances have a higher enthalpy of vaporization, meaning it takes more energy for them to boil. They boil upon entering the cylinder, due to the vaccum created by the piston going down, however they take more energy in the process, cooling down the cylinder. This is especially pronounced on methanol power dragsters, where the engine temperature is actually cooler at the end of the run than it is in the beginning.
This has advantages or disadvantage. On one hand the cooling of the cylinder allows the engine to run harder, due to boost, ignition advance, or whatever. Thats where the resistance to detonation comes from. On the other hand, if the cylinder is colder, more of the energy of combustion goes to heat it up, leaving less to push the piston down, which robs power. This effect is considerably more apperrent than the btu's/liter difference

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post #7 of 9 (permalink) Old 11-12-2007, 12:49 PM
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Alcohol is a separate issue - yes it will boost octane and it is sometimes used for such in small amounts, but normally it's added as an oxygenating agent as a replacement to MTBE in most places. Normally the alcohol admixture is across the board for all octane ratings. Aside from boosters, octane in gasoline is controlled by the ratio of octane (the principal hydrocarbon in gasoline) and heptane. In fact, by definition octane (the number) is the percentage of octane in an octane/heptane gasoline blend.

But I agree with your points - alcohol dilutes the energy content of gasoline, and causes it to burn cooler.
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post #8 of 9 (permalink) Old 11-28-2007, 03:32 AM
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How about going -1 down up front, will my MPG improve or suffer?
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post #9 of 9 (permalink) Old 11-28-2007, 04:24 AM
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Originally posted by loneryder
How about going -1 down up front, will my MPG improve or suffer?

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