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Discussion Starter #1
So yesterday I took a couple hundred mile round trip for a fish sandwich. Along the way I stopped and got some gas. It was pretty pricey so I went with regular. I've done it before when it's cool out or when high test isn't available and never had any problem. The bike has a pretty low compression ratio, so I find it kind of surprising that Vic recommends it, but they do as I recall.

Anyway, it was reasonably cool and I wasn't running it hard, but at one point I did ask it to make a quick pass and as it approached redline I could hear it start pinging. I filled her back up with Premium today. As I did I got a question that keeps coming up when I get off it. "Hey dood, who makes that Victory? It sure is a pretty bike."

"And they shall know my name is Victory, when I lay my vengeance upon them."
 

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OMG, another octane thread. That pinging is Ma Vic's way of telling you that you are a bad boy. Run too low an octane too long and you'll eventually burn holes in your piston tops. The pinging you heard tells you the gas is exploding, rather than burning, as it should. Think about the pinging you didn't hear. C'mon, you spent around $16,000+ for a toy, what's a few cents more for a tank of premium?
 

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Come on now Ricz! He saved (at the most) a dollar ... .20 cents per gallon times five gallons.;)
 

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Even though my XC takes premium, I spend less on fuel than I did putting regular in my VTX, my XC gets phenomenal mileage compared to my VTX:crzy: mid 40's to low 50's compared to low 30's to upper 30's:D
 

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I find it harder and harder to find 92+ oct and have to run the plus that is 89-90.Seems to do ok but when I find 92 or better I do fill up.
 

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I have a station right down the road that sells 100 octane racing fuel. Can't understand why my gas mileage decreases when I use. Btw, the bike absolutely runs great with it.
 

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I have a station right down the road that sells 100 octane racing fuel. Can't understand why my gas mileage decreases when I use. Btw, the bike absolutely runs great with it.
Is there ethanol or another alcohol in that racing fuel? If so, that will explain the mpg loss. Another reason for the loss might be in the name and you have been influenced to roll on more throttle. dance 1
 

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Running higher octane when you don't need to, will help you build carbon on the pistons.That is why when you run lower octane it pings. There are lots of Vic's out there running regular with no ill effects. I have to run premium now with the high compression pistons, and have to run octane boost with it when it gets over about 100 deg here.
I used to run regular when I had stock pistons and never had detonation.
Kevinx explains this way better than I can, but he is adamant that you do more harm than good by running too high of an octane rating when you really don't need it.
 

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I was curious if I could run 87 octane without detonation. It would seem you could with the rather low comp ratio, but if some of you are getting detonation, then they are obviously set up with pretty advanced timing. If you are running 87 with no det you will make more power. As for 100 oct on a stock motor and running better, it's all in your head. Your making less power and going slower!
 

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Discussion Starter #14 (Edited)
I was curious if I could run 87 octane without detonation. It would seem you could with the rather low comp ratio, but if some of you are getting detonation, then they are obviously set up with pretty advanced timing.
Must be. As I said previously, the bike runs fine on regular in normal operation. I had to do it once before because I needed fuel some place that didn't have an alternative. Only near red line did the bike protest, but protest it did.

FWIW, I've had FJRs and Goldwings that are supposedly designed to run on regular do the same thing, though they will ping just rolling on the throttle hard far before their red lines. More like when the engines are being slightly lugged.

If you are running 87 with no det you will make more power. As for 100 oct on a stock motor and running better, it's all in your head. Your making less power and going slower!
For those not in the know, higher octane means less volatile fuel. This prevents ignitions not due to the normal flame front generated from a spark plug. Igniting fuel at the wrong time in an engine cycle or causing a haphazard flame front can damage to it.

Ignition of fuel is a function of both heat and compression. Less volatile, doesn't mean that there is necessarily less energy per unit of fuel, just that it takes higher compression/temp to get it to ignite.

When the ignition timing is advanced, the flame front is produced at a time when the running compression of the engine is higher. The compression, heat from the engine, heat from the flame front can cause the flame front to change from a nice linear burn to a haphazard burn that can cause damage. That's what TorqueMonster is referring to.

One thing to note about compression ratios. The ones defined for spec sheets are static ratios i.e. the area of the cylinder at top dead center (TDC) to the area at bottom dead center. This is around 9 for our Vics but can go to 12 or 13 on some high performance bikes. A higher value is usually a pretty good indicator for the need of high octane. But one has to be careful not to conclude that the static compression ratio is equivalent to the running compression ratio. Think of adding a turbo charger. By pushing more air into the confined space at TDC, the running compression ratio will be higher for a turbo charged engine than for a naturally aspirated engine with the same static compression ratio. The same is true to a lesser extent for less dramatic mods like free flowing air-filters and exhausts.
 

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Well said Saddlebag and worded so it is easily comprehended. As one who reads a lot about things others consider mundane (batteries, oil, fuels) I know those things about octane ratings and its effect. But I do have 2 questions: 1. If using an octane higher than the engine actually needs, will there still be burning and expansion of air after the piston reached BDC and starts its way up again, resulting in a loss of power? 2. If using an octane that is too low, will the expansion of the air cease before the piston attains BDC also resulting in a loss of power?
 

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Discussion Starter #16
Well said Saddlebag and worded so it is easily comprehended. As one who reads a lot about things others consider mundane (batteries, oil, fuels) I know those things about octane ratings and its effect. But I do have 2 questions: 1. If using an octane higher than the engine actually needs, will there still be burning and expansion of air after the piston reached BDC and starts its way up again, resulting in a loss of power?
I have no data to prove it, but I would think not. Again, octane is all about the temperature/compression needed to ignite the fuel, not the energy in a given cylinder full of gas nor the rate at which it is consumed.

2. If using an octane that is too low, will the expansion of the air cease before the piston attains BDC also resulting in a loss of power?
Sorry Ricz, you lost me on that one. The same amount of air pushed into the squish during the piston compression stroke will be there on the way back down following ignition. It will just be filled with by-products from the chemical reaction of the burn rather than raw fuel mist.

Anyway, as is often the case, we motorcyclists are a tinkering bunch. Some put on straight pipes, others bicycle tires, others balloon tires, others monkey bars. Its all part of the grand experiment to see what works or at least what we can tolerate in the journey to becoming a way kewl dood.

Some of us are just tight wads like the car tire guys and me. I took a chance to see if I could get away with running regular in cooler weather and found that I can if I don't push it. But since I can't guarantee that I won't want or need to push it on any given ride, my fill-ups will be comprised of high test from here on out. Unless I'm running dry and can't find any...
 

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Saddlebag, my research has me believing that octane has only to do with the rate of the burning - the higher the number, the slower the burn. The burn, or flame front, heats the compressed air, expanding it and in turn, that expanding air pushes the piston down the cylinder. Hence, my questions re using too high or too low an octane. What I expressed in question form, in post #15, is my theory of what occurs when improper octane is used. Can anyone refute it? If too low an octane is used, an incomplete expansion results, causing a loss of power compared to a proper octane. Too high an octane has the air expanding for too long a duration, possibly still expanding after the piston is on its way back up the cylinder. Resulting also in a loss of power. Does that sound reasonable?
 

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Discussion Starter #18
Saddlebag, my research has me believing that octane has only to do with the rate of the burning - the higher the number, the slower the burn.
http://www.rockettbrand.com/techsupport/documents/TechBulletins/FlameSpeedOctaneAndHpRelationships.pdf

"Octane Number: The octane number of a gasoline has little to do with how fast it burns or how much power the engine will make. Octane number is the resistance to detonation. If the octane number is high enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame
speeds and some with slow flame speeds. It depends on how they are put together. At Rockett BrandTM, we like fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline than one that has a slower flame speed."

Petroleum Proof, High-Performance Gasolines

Popular Hot Rodding Magazine, January 1998
By Scott Parkhurst

Octane is a measurement of a fuel's resistance to ignition. Ideally, the air/fuel mixture will ignite at the proper time and burn smoothly through the power stroke. The idea is that one powerful combustion of the air/fuel mixture is better than several randomly-ignited small flame fronts. When you can precisely control the point at which the fuel will ignite, maximum performance of the engine can be achieved, and power-robbing knock and ping will be eliminated. Knock and ping are a result of abnormal ignition, or multiple flame fronts colliding within the combustion chamber during the compression stroke.

http://www.nsxprime.com/FAQ/Miscellaneous/FuelAdditives.htm

"The burn rate of a fuel is a measurement of the time required for complete combustion of the air/fuel mixture. The notion that octane ratings affect the burn rate of fuel is about 180-degrees from reality; burn rate is a function of several variables, and the two are completely independent, although there is generally a correlation between octane ratings and burn rates."

Saddlebag - IOW, race gases tend to be blended to have *both* fast flame rates and high octane, because the fast flame rate provides higher performance and the high octane allows it to be used in high compression (i.e. high performance) engines without detonation. It's kind of like mixing chocolate and peanut butter. Just because they exist together in a single product that tastes great, does not mean that one has anything to do with the other.
 

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race gas

Will the 100 octane not burn up your 02 sensor's? I figured the lead in the fuel would wreak havoc on the machine.
 

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Discussion Starter #20
Will the 100 octane not burn up your 02 sensor's? I figured the lead in the fuel would wreak havoc on the machine.
As far as I know, lead damages catalytic converters. I think the elimination of lead from gas pre-dated O2 sensors in the US so there probably isn't a lot of info on it.

While I was in Italy, there were still places advertising leaded gas. Still pictures of topless girls behind the clerk too. Reminded me of USA circa 1974. Anyway, their cars must be okay with it. I doubt they are still using carbs over there.
 
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