Which Octane are you running? School me.

[Gunz]

I've been running 91 in my raptor, but today I was told to run a higher octane by a Yamaha mechanic. I'm running stock bore and stock compression. I was totally thrown off by this. SOOOOOO, I'd like some good input from you guys on this. Also what Octane are you running in your motor and why? I would also like to know when I should jump my octane numbers. Example 87-91 at stock-11:1, 93-100 at 12:1 w/pp, 100-110 w/14:1, pp, big bore.......and so on.  I see so many people just throw race fuel in their tank, tilt their head and ride, but can't answer why they are running it except for bragging rights.


Basically I'm looking to get schooled in "Octane 101".

[tonto13]

Also want to know this! I know elevation plays a role in this to but to what extent?

[gr8ride4u2luv]

I have a good amount of mods. 11:1 CP piston and I decked the cylinder. I run 91 octane NO problems. The only thing I can think of to run a higher octane fuel is because I like the smell! 

[Sand84]

Anything more that 87 on a stock raptor is a waste.  Im pretty sure the owners manual says 87.  If i had it with me I would look..  I ran 87 on stock..  93 and 110 mixed with a 11:1, PP head and Hot cam stage 2. And now with mods in sig I run 110.. 

[1badazz_700r]

  you dont need anything more than 87 octane. Iam running VP 105(red) with mods in my sig

[Peelz]

sand and badazz are 100% corrrect. High Octane is useless with low stock compression.  Some people think Octane will boost power, but that is untrue. Higher octane is only necessary as Compression rises. I use 87 or 89, occasionally 91. Friend gave me some 105 and it made no difference, but smelled cool.

[Gunz]

These are great responses but ........ why?   

Sand...... why did you run a 93/110 mix with a 11:1, I was told a 91 would be fine. Why are running 110 now with your mods?

Badazz..... Why are you running 105 with your mods?

Peels your getting close, but I'm looking for octane to compression ratios and/or air to octane formulas..... whatever it takes to find out what and why I need a certain octane for certain mods to a motor.

  I know people use race fuel for certain mods, but I'm looking for the reason why they use 110 vs 105 vs 1000 or whatever.

Example If I did a 14:1 with a stock bore and a mild PP, lets say with a HC3 and a +2 TB, what octane should I run and why? What if I changed the valves to a + 1 and bored it out to a 105 and 12:1 piston?

See what I'm getting at? My point is I know that I'm going to need to run a higher octane with 12:1 compression or bigger, but I don't know why except for the simple reason of somebody telling me I need to. Whats the madness behind the reason.

[Colorado700R]

The four most important properties of racing fuel  from the VP Racing fuels website

You can't make a racing fuel that has the best of everything, but you can produce one that will give your particular engine the most power.  This is why we produce different fuels for different applications.  The key to getting the best racing gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine.

1.   OCTANE – This is simply the rating of a fuel's ability to resist detonation and/or preignition.  Octane is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON), and Pump Octane Numbers (R+M/2).  Pump Octane Numbers are what you see on the yellow decal at the gas stations and represents an average of RON and MON.  VP uses MON because this test method is more relevant to racing.  Most other companies use RON because it is higher, easier to come by, and sounds better in marketing messages.  Don't be fooled by high RON numbers or an average -- MON is the most important for a racing application.  However, the ability of the fuel to resist preignition is more than just a function of octane.

2.   BURNING SPEED - The speed at which fuel releases its energy.  In a high-speed internal combustion engine, there is very little time (real time - not crank rotation) for the fuel to release its energy.  Peak cylinder pressure should occur around 20° ATDC.  If the fuel is still burning after this, it is not contributing to peak cylinder pressure, which is what the rear wheels see.

3.   ENERGY VALUE - An expression of the potential in the fuel.  The energy value is measured in BTUs per pound, not per gallon. The difference is important.  The air:fuel ratio is in weight, not volume. Remember, this is the potential energy value of the fuel.  This difference will show up at any compression ratio or engine speed.

4.   COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization.  The higher the heat of vaporization, the better its effect on cooling the intake mixture.  This is of some benefit in a four-stroke engine, but can be a big gain in two-stroke engines.

[Peelz]

4.   COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization.  The higher the heat of vaporization, the better its effect on cooling the intake mixture.  This is of some benefit in a four-stroke engine, but can be a big gain in two-stroke engines.


This is why banshee guys don't shut up about race fuel. Then look at me funny when I decline to use it.

[Sand84]

These are great responses but ........ why?   

Sand...... why did you run a 93/110 mix with a 11:1, I was told a 91 would be fine. Why are running 110 now with your mods?

Badazz..... Why are you running 105 with your mods?

Peels your getting close, but I'm looking for octane to compression ratios and/or air to octane formulas..... whatever it takes to find out what and why I need a certain octane for certain mods to a motor.

  I know people use race fuel for certain mods, but I'm looking for the reason why they use 110 vs 105 vs 1000 or whatever.

Example If I did a 14:1 with a stock bore and a mild PP, lets say with a HC3 and a +2 TB, what octane should I run and why? What if I changed the valves to a + 1 and bored it out to a 105 and 12:1 piston?

See what I'm getting at? My point is I know that I'm going to need to run a higher octane with 12:1 compression or bigger, but I don't know why except for the simple reason of somebody telling me I need to. Whats the madness behind the reason.

I ran mixed with the 11:1 cause it kept the motor alittle cooler and it smelled good ..  I'm running 110 now do to my compression.

If you do that stockbore build u talked about it would need 110 depending on elevation .. 

[Kenny]

These are great responses but ........ why?   

Sand...... why did you run a 93/110 mix with a 11:1, I was told a 91 would be fine. Why are running 110 now with your mods?

Badazz..... Why are you running 105 with your mods?

Peels your getting close, but I'm looking for octane to compression ratios and/or air to octane formulas..... whatever it takes to find out what and why I need a certain octane for certain mods to a motor.

  I know people use race fuel for certain mods, but I'm looking for the reason why they use 110 vs 105 vs 1000 or whatever.

Example If I did a 14:1 with a stock bore and a mild PP, lets say with a HC3 and a +2 TB, what octane should I run and why? What if I changed the valves to a + 1 and bored it out to a 105 and 12:1 piston?

See what I'm getting at? My point is I know that I'm going to need to run a higher octane with 12:1 compression or bigger, but I don't know why except for the simple reason of somebody telling me I need to. Whats the madness behind the reason.

You are gonna hate me for this answer........ The larger bore will normally require a little more timing to offset a slower burning rate due to the larger area, that in return, will require more octane for the increased spark lead time. Boring the engine can increase heat transfer which will need less.

Adding larger intake valves can increase dynamic compression due to more charge getting into the chamber, increasing the tendency for detonation....more octane......unless you improve the mixture quality along with quantity=less spark lead......less octane. An 11:1 piston with a big dome and loose quench may need more octane than 12:1 flattop with extremely tight quench. Crevice volume around the piston crown has an effect.
This list could go on forever. Add the fact that octane boosting chemicals lose effectiveness over time.

Hell, 93 octane could have better knock tendencies than 100 octane if the 93 is fresh, but the 100 has been in storage for a year. No two gas brands seem to have the same vaporization point, or anything else for that matter. Now we can put oxygenated vs non-oxygenated into the mix. Condition, or effectiveness of the rings change the requirement depending on how much oil may be getting into the mix, and the level of detergent in that oil.....

You are gonna find some generalizations that are okay, like cooler chamber temps, higher elevation, and tighter quench reduce octane requirements. Some of them are totally wrong. For example; Tighter lobe centers bleed off compression therefore reduce octane requirements. This is partially true if you only ride at part throttle, but at full throttle the increase in dynamic compression makes the problem worse.

We have a general set of guidelines due to experience with this particular engine and that experience lets us know what to expect (within reason). I want to see you stay in a fairly safe zone for pump gas. You will make more power and have better throttle response with a lower compression engine with proper timing lead than you would get with a higher compression engine with compromised timing curves for compatibility with low octane.

I know this sucks to hear, but it is gonna be trial and error on each application when running at the limits. Engine builders have a pretty good grasp on what works best on their builds because of this trial and error testing.

This question kind of ranks up there with "How far is up?" 

[NaturalRaptor]

Excellent info as always everyone! 

[fire raptor]

So this is why I do not modify my Raptor engine. Where I ride I have bought gas out of drums behind a shack or out of the back of a pickup truck parked on the side of the road with Se Vende Gasolina sign in the window. With the low compression of the stock engine and no mods we can burn 181 rum if needed.So you boys get over to the Auction and spend some $$ for a good cause.

[Gunz]

I wanted to see if there was any difference of running 87 to 110 in my raptor today. I ran 1 gallon of 87 through my tank. Then I ran a gallon of 91 through it. Next I ran a gallon of 101 through it. Last but not least a gallon of 110. After running through all of these octanes I was convinced I literally wasted $34 of my hard earned money. I tested these fuels on trails, wide open dunes and drag racing. The drag races were the best proof. I raced the same bike on each run with the same driver on the same track and pulled 4 lengths every time. The only positive result I had was the smell. Race fuel = Smelly good.

[Krandall]

mmmmmmm 110.