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While ridding in Ma & Pa Kettle country last summer I was forced to buy regular unleaded gas for my 1999 FXDS. Now I know there is no likely damage from running one or two tanks full of this stuff, but I thought it was kind of funny that I did not notice any difference in the way my motor ran. Running in hot desert country and climbing out of the Columbia River Gorge produced no strange noise or detonation. Same thing when crossing the Cascade Mountain Range into Puget Sound Country. What gives? My handbook says to run only premium unleaded, which I have except for this one time. Is the motor company not telling the truth about which gas to run and why?
 

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The company is telling the truth. Always run the premium gas. When you actually here the detonation it is really, really bad. The air density also determines how bad detonation is. Also, if you ride without a windshield you probably will not hear the pinging.

In my opinion regular gas should be 93 octane and premium 105. Gas they sell now days is not much for air cooled motors. Airplanes run at least 100 octane and their motors have the characteristics of motorcycle motors. Plus they have alot better cooling flying at 100 mph.
 

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I find it amusing that so many people know so little about octane. I think the average consensus is the higher the better. Why is that , because it cost more? Simply, octane is a retardant. The higher the octane, the harder it is to ignite. Believe it or not, a lower octane fuel is a hotter fuel. The purpose of it is to prevent pinging or pre-ignition. Don't get me wrong, pinging is very, very bad. What is happening is the compression is igniting the fuel before the piston is top dead center. That is an engine destroyer!!! On the other hand you want good clean combustion. You don't want a lot of extra additives, read alcohol, in your engine from a fuel with too much octane. Harleys are not airplane engines. They are both air cooled but airplane engines have much higher compression, thus the need for such high octane. There is a reason why you can't get the higher octane fuels in the mountains. The air pressure and oxygen content is lower so you need a hotter, read lower octane fuel. They are doing you a faver! Don't sweat it, ride your bike anywhere you want to go and buy the fuel that is available. Its just what you need. I'll close with a good rule of thumb. I got this from a gasoline engineer who worked for Harley. It works for Harleys, cars and even airplanes. Use the lowest octane you can burn without pinging. Thats usually going to be the middle grade for Evos and 93 for Twincams. Remember though that is for sea level. The rules change in the mountains.
I hope this helps.

Hoghead4ic
 

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I find it quite amusing that your penny-pinching gas buying has not caused you to change a piston yet. You are 100% correct about detonation so i cant figure out why you dont promote high octane gas. You are also correct about riding in the mountains. Living in MS though you should probably think different. With temperatures reaching 100 plus and humidity at 100%, detonation is just around the corner. I have changed a lot of pistons that detonation has totally destroyed. I dont think that sacrificing premium gas for regular is a smart thing to with a expensive motor. If you are more worried about a little carbon build up due to additives than detonation, go for the regular. Just dont complain when the ole ultra cracks a ring.

I am not familar with the new efi system on Harleys. If it has a knock sensor like automobiles, when ever there is a slight ping it automaticly retards the spark timing. When the timing is retarded you lose power. Not my ideal way of riding a motorcycle.

By the way, aircraft engines do not always run high compression. Most all of them run 8.5 to 9.5 unless they are competition motors. What compression ratio does a stock twin cam have? Detonation and valve wear is one reason why aircraft burn low lead 100 octane fuel.
 

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One more note.

I will agree with hoghead about buying gas. Buy what is available and dont sweat it. If it gets hot where you ride I would suggest runing the higher octane gas. If the Harley engineers put it in the manual they done it for a reason.
 

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The higher the octane, the harder it is to ignite.

Not so, perhaps you meant to say "the higher the octane, the slower it burns"

Other then that you are mostly correct from a chemists point of view.
What your friend failed to say is that there is detonation and then there is high speed detonation. You will never hear the latter, but it will do a number on your engine.
You can certainly tune a relatively mild engine to run on regular fuel, just like you can tune it to premium fuel. The engine will make more power on higher octane fuel, not because the fuel is any better, but because you can use more agressive settings.
Since most people have no idea what the exact state of tune of the engine is, including the factory due to mass production variances, it is cheap insurance to run premium gas. You may well find engines that apparently run fine on regular, but are they?


The other big scam in the US is that the octane number posted on the pump is the average of the research and engine octane number. There is a big difference in how you get to this average number. A fuel with a higher engine octane and a correspondingly lower research octane will be much more detonation resistant then another fuel with the same pump number achieved the other way around.

With all these variables one would be well advised to take the conservative approach.
 

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Thanks guys, lots good info. I have always used prem, the trouble is in Calif. the best octane is 91.:mad:
 

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Well, I'm in Napa (@35mi) and 91 works in my hi- compression EVO just fine. I am running the most aggressive curve available on the SE selectable module and I don't ping.

Give us a yell when the weather is good we'll get together for a ride.

manny
 

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Bigtime I suggest you read my thread again! Did I say anything about pinching pennies? I ride Harleys man, thats not exactly a penny pinching lifestyle. I don't care what gas cost. There are two Harleys in the garage and my wife and spend all our vacations on them and all our leasure time. Trust me, gas is our least expense!
Again, if you go back and read, I suggested 91 to 93 octane for most applications. I was simply responding to a fellow bro who was concerned about not being able to find it in certain areas.
And yes I live in MS but I ride several thousand miles a year in many other states and I buy whats available. Whats the alternative, staying at home? Not me brother.
Lastly, chill out. If I somehow offended you, my apologies. I just know for a fact that these bikes will last a long time without using airplane fuel.
We all want our bikes to last a long time so we want to do whats best. Buy what fuel you think is best but don't let the availablity of higher octane fuels in certain areas rob you of your joy of riding.

Have fun and ride safe,

Hoghead
 

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Thanks for all that great info guys.
So if I continue to keep using the hishest octane at the pump I will be doing my bike (96FLTCUI) a big favor in the long run ?
 

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Heh! You can always buy an octane booster and add it as you see fit. Most late model cars and trucks now have an octane sensor which adjusts the injectors to compensate for octane and altitude. Rule of thumb: If it's air-cooled run high-octane. If it's water-cooled, run what you want.
 

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So if I continue to keep using the hishest octane at the pump I will be doing my bike (96FLTCUI) a big favor in the long run ?


Maybe, maybe not. Thing is, you don't want to find out. I run the best I can find at any given time, but I set the bikes up fully knowing that at times the fuel quality may be very poor, so I don't have to worry about it.
I feel EFI bikes would be more sensitive to it, as they generally run lean on top.
Another option is to adjust your riding style when you have poor fuel in the tank.
 
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