my 04.5 600 with 4 deg adv. and all the 800 bolt ons runs poorly, idle drifts, with anything above 89 octane. in my area we have 87, 89, 91, and 93 available.

 

Iwrote this for a snowmobile forum and have posted here:



Well I will try to give you a short version of this :
premium gas was and is designed to protect your engine against detonation. and it does this because of the chemical makeup of long branch tightly bonded molecules. Where regular gas has a molecular structure that has less of a bond.
The chemical composition of the fuel determines how fast the fuel will burn and if it will work well with high compression or temperatures.
fuels with weak molecular structures [regular] will break down more quickly or burn spontaneously [detonation] at lower temperatures.
Fuels with tight molecular structures [ premium] burn more slowly and take more pressure and heat to fully break down and burn.
therefore putting premium fuel in a engine not designed for high octane fuel [I e not having high compression or spark advance ] will not be able to break down the chemical bonds. And will not completely burn the fuel charge therefore produce less power.
So you see next time your at the pump buying that 115 octane racing fuel for your sled that costs five dollars a gallon. you may want to reconsider. And by the way no fuel can be over 100 octane ! It's a percentage
Run the type of fuel your manufacturer recommends !!!!!

 

zbart-
you got me curious, how can the octane rating not be more than 100? You say it is a percentage, but what is it a percentage of? I've heard that WWII fighter pilots used 140 octane or so fuel in their planes.

 

while your write up on octane is mostly correct, it is not a percentage at all. here is the answer to everyones questions

http://auto.howstuffworks.com/question90.htm

 

Well I’m not always good at this but here is a short version of how fuels are evaluated WIscrambler .

The reason a numbering system was introduced was because aircraft engines in World War One would run just fine on one batch of gasoline and would suddenly self destruct though detonation and punch holes in the pistons on the next batch of gas. Worse yet was that the fuel appeared to be the same, weigh the same and come from the same refinery!

Fuel companies tried chemical analysis and a number of other tests but were not able to weed out the batches of fuel that would produce detonation. So they produced special fuel research engines with a variable compression features to evaluate and grade fuels.
Basically these engines would have their compression raised until they produced knock and then a anti knock number would be applied called a Highest Usable Compression Ratio or HUCR
Even with the same engine given to all fuel labs, it was discovered that differing HUCR numbers would come out of the same fuel batches at different locations. So what was needed was a unvarying standard to calibrate these engines. Two pure substances were chosen as reference fuels. The high reference fuel chosen was iso-octane and the low reference fuel was heptane.
So a batch of fuel would be run on a variable compression engine and it’s HUCR numbers recorded. Then a series of runs would be made with various mixtures of iso-octane and heptane until a blend was found that produced a HUCR number identical to the fuel being tested.
At this point the fuel would be rated in relation to the PERCENTAGE of iso-octane used in the reference fuel mixture that gave the same results. For example a test fuel that had behaved the same as a mixture of 83% iso octane and 17% heptane would be called 83 octane fuels.
This is the percentage I was talking about. More about this later.

Since this time new more modern test procedures are used called the research method and motor methods. Both us the same variable compression engine but the motor method uses faster engine speed and higher inlet mixture temperature then the research method.
This is important if you’re into racing as the motor test gives Motor Octane Numbers (MON) is more severe and generally gives numbers 6 to 12 less then the research method Research Octane Numbers (RON)

So when you go to the pump what you get is a combined rating of the RON + MON / 2 which gives you a good balance between the two methods and driving conditions.

Now if you’re not bored out of your mind I will explain that NUMBERS OVER ONE HUNDRED CANNOT REFER TO PERCENTAGES OF ISO-OCTANE. They are in fact performance numbers devised to extend the scale of anti knock measurements past what is possible with pure isooctane’s and as such they are an estimate of the number. That is what I was getting at earlier, I’m not saying a C16 fuel can’t have a number higher then 100 all I stating is it’s an estimate, probably a good estimate but none the less a estimate!

The supercharge test is the test that they use to get numbers over 100. The supercharge octane number (SON) is the test that airplane fuels are given and go all the way to 300.
Since two tests are involved these fuels the F3 and F4 test these fuels are given two numbers such as 100/130.the first number being the F3 simulates a engine being supercharged at a cruising speed while the F4 is a higher supercharged engine at a richer mixture to simulate take off or during combat conditions
For example a 100/130 rating has the potential of increasing a aircraft engines performance by30% over that possible with pure iso-octane fuel.

While some companies actually blend race fuels and apply an estimated number ie; 106 most mix av gas or airplane fuel at 110/140 with a base fuel and additives then apply a rating they come up with, basically as an estimate of the blend.

I hope this was not to boring ……..but there you have it

Zbart1

 

Wow, too much info! Just want to add that gasoline looses one octane point for roughly every 45 days it exists. If you are far from a pipeline and the station you buy from isn't very busy turning over his product you are not getting what you think you are. Stale gas loses it's "potency" and gums up the fuel system with deposits.

 

Wow Zbart1 very impressive!!! Although I must say I grasp the basic's there but I would be a liar if I said I totally understand that. I have to ask are you a chemist or something??? I'm being serious here,,,not trying to be a smart *** at all. To be honest alot of it was like reading Latin to me, but I can tell you know what your talking about....Again great post,,,Kerk

 

Thanks Kerk ……..not a chemist but I’m a mechanical Engineer. We have two refineries in my town and have worked at both.

The truth is I used to race snowmobiles with turbos and Nitrous and Nitro Harleys and did a ton of research into fuels back in the day. We used to have a hell of a time with fuels under these conditions and I learned a lot from a lot of knowledgeable people and a ton of books.

 

I have a 04 600 and would like to keep out of the motor in my persuit of HP, what did you do with the timing? What is factory? What did you do and did it help.... don't spare me the details. What are the 800 bolt ons?

 

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