The owners manual and the service techs tell you to use the highest octane available at the pump if not the tires may fall off, the battery will stop battin', the generator will stop gennin' all kinds of mean-n-nasty things will happen to you, your bike and your family!

Fearing physical andfinancial disasters reminiscent of the stock market crash of '29 I have always used high test gasoline in my 06 Street Bob. I ride kind of hard, onopen roads I'll run around 75 to 85 depending on the road and who is riding with me. In town I take off kind of fast compared to the cages around me. I've been averaging around 35 to 36 MPG using high test.

Someone posted a question about octane and feed back was everything from, "I'll use a mid grade onlyif nothing else is available and just enough to get me to a station that has high test" to "Use the lowest octane you can use as long as your bike does not ping."

The ones backing the high octane use the ownersmanual,servicemanual, service techs and the sales person to support their side.

The ones supporting lowest octane side show studies by not only service centers but studies made by collages, universities and oil companies too, supporting their side.

Well I decided, sense I'm thinking of trading my Dyna on a Deluxe I would do a little experimenting. Irode north of Sebring, Fl, about 120 miles from home, before leaving home I filled up with 92 octane, 3.4 galsat the Sunoco station just a mile from home. I rode 122 miles. Stopping at a BP station I filled up, 3.4 gals of mid-grade, 87octane.

I averaged 35.88mpg for the 92 octane.

Returning home I filled up at the Sunoco station by my house. The bike took only 3.053 gals of regular gas. 83 octane. that comes to 40.288 mpg on mid-grade with no pinging. not only did I get almost a 5 mpg increase, I really think the bike ran cooler? I have no way to verify that statement, it just didn't feel as hot on my legs riding back.

I'm getting ready to leave the house of a short, around town run today and will fill up tonight and see what kind of mileage I get and see if there is any pinging withthe regular grade of gasoline.

 

I'm trying this experiment myself. we'll see what happens but for now, I'm just going down to 89 octane. There was a good post the other day about octane ratings and compression that made a lot of sense. Think I'll go try to find it again.

 

I'll stick with premium.That is what the MOCO specifies,and only costs about a dollar more at fill-ups.
Clark

 

http://en.wikipedia.org/wiki/Octane_rating
I found the link about octane ratings. I agree with the forum members about the price issue. What's another 10 or 20 cents a gallon in a 4.8 gallon tank? I just want to know the scientific facts behind the whole issue so I can make my choices rather than popular misconception. I always thought that higher octane meant better perfomance but, I've read a few things lately that suggest lower heat, better mpg and less $$$ with a lower octane and I want to find out if it's true. As for the Harley manual recommendation, they've made it quite clear that they'll do and saywhatever it takes, to keep the EPA off their backs.

 

I have always used the cheapest gas around here (87 octane ) for my carbed 98 FLHT. The manual calls for 87 min. for carbed bikes and 91 min.for injected. Never had any problems with engine knock or pinging and on my most recent trip was getting a min. of 45 on the highway. I don't have any scientific evidence on fuel but I have always been told don't treat your vehicles to better fuel than what the manual suggests for a stock or slightly modified ride.

 

Im not sure how the MOCO programs the ECUs on theses things but, I know for sure that alot of cars
have more than one timming map in the computer.

When the engine senses some knock it will just retard some timming.
The car i was playing with actually had 4 timming maps in her!

If HD did this then one could safly run any octane with little notice of detonation.

 

I've always used premium in my bikes, but one time I put premium in my 97 Nissian Maxima that uses regular and the mileage went down. I'm afraid to try regular in my bike because my hearing is shot and I don't think that I could hear it if it pinged.

 

There's an interesting article in the Scientific American magazine this month about automotive fuels and whether or not you need premium fuel. One conclusion was that premium was a mis-nomer, there is actually more energy in regular octane gasoline. The word "premium" is an invention of the oil industry to justify having you spend another 10-20 cents a gallon. You do get a higher octane rating, but do you need it? Almost all automobiles in the last ten years or so will run very well on regular octane fuel.
Some years ago the cheaper brands of regular fuel often did not have enough injector cleaner in them to mainain the emissions standards, so the federal government changed the laws to require more cleaner in regular fuel. Your injectors will stay clean with regular octane fuel these days.
Another misconception is that one brand is superior to another. Keep an eye out when the tanker truck comes to refill the fuel station's tanks...chances are very good there is no brand name on the truck. There are only a few refineries anymore, and they supply all the fuel stations. One brand may specify more of some additive than another, but the fuel comes from the same refinery. Getting a bad tank of fuel is possible, but chances are it is not the brand's fault.
If your machine does not ping on regular fuel, it will not hurt anything to use it. If it does ping, then try mid-range. If it still pings, then use premium. If there is no pinging, there is no advantage to premium fuel, it just costs more and has less energy in it.

 

The key word is detonation compared to engine cylindercompression.If you are under 9 to1 comp.say 8.9, 8.7 to 1 you reallydon't need the higher octane. Lets look at the defininition of detonation.

1 : the action or process of detonating
2 : rapid combustion in an internal combustion engine that results in knocking
Now lets look at detonating

It's all about compression, fuel, heat,spark timing and octane. To gain more power we have to up the compression and or get more fuel air mixture in the cylinder. Here is a link that youcan go to and read about it. You really need to understand how it all works together to make the right choice onfuel octane requirementsover or under a manufacteurs recommendation and or an engine that has been modified.

All thingsin motors effect anything not stock as well, so anytime you modify even just the exhaust or intake, sparkplug heat range etc.,,,,,something changes so it's not always just the fuel, it's the AFR that comes into play as well. Study andresearch all you can on this stuff and you'll figure out what your needs in fuel is and the signs of how to look for it.

http://zhome.com/ZCMnL/PICS/detonation/detonation.html

 

John,

The TC96 has a compression ratio of 9.2:1
Sounds to me like it is right on the edge of the needs premium range. Think I may try a tank or two of regular and see what happens. Not sure how the corn oil (ethanol) will effect this though......