Does 100 octane make a difference???

28 replies to this topic
  • gonzo

Posted October 26, 2004 - 06:45 AM


I'm editting this post because maybe I was clear enough. If you run high octane gas and dont have the compression to burn it, it simply wont burn and you'll run rich. If you decrease the amount of gas, even though you have less to burn, it doesnt mean you can now burn it because there's less. If you dont have the compression you simply wont burn it. If you dont have enough gas you might just not get the bike to even run.

  • ncmountainman

Posted October 26, 2004 - 06:55 AM


well if the toluene mixed fuel will be denser thus requiring leaner jetting(same compression) than it only stands to reason that your making the same amount of power with less fuel,i'm no physicist but it would only make sense? :cry: well alright if you were to mix the toluene with 85 octane instead of 93 you would use more toluene to get the gas back to or exceed 93 , so with the new found denser fuel with the same octane rating you would have to lean the bike and use less fuel for the same results?

  • Rich_Rohrich

Posted October 26, 2004 - 09:55 AM


well if the toluene mixed fuel will be denser thus requiring leaner jetting

If you can vaporize it that will be the case. So in an application like a V8 Dodge with long hot intake runners and a 5500 peak rpm you'll have plenty of time and plenty of heat to vaporize even the heavy end components in pump fuel or toluene.

The intake tract is really short on the YZF, really cool (in relative terms) and the available time at 7000 + rpm just won't provide the heat needed to vaporize heavy high temp components in pump fuel or when they are added to the fuel. The end result is adding these types of heavy high temp components actually requires you to jet RICHER even though they have a higher density. I know that probably seems counter-intuitive but air/fuel ratio is ultimately determined by how much fuel by weight is available in the chamber in a usable state. Fuel that is still in a liquid state in the chamber will provide excellent piston crown cooling effects in a two-stroke (where it is really needed), but in a four-stroke it just leeches away usable heat and ends up as carbon deposits somewhere down the line in the exhaust. It won't contribute to the reaction so it it takes additional fuel to ensure enough light components make it to the chamberand can be reacted with the available oxygen.

VP Red is a poor choice for high speed water cooled singles for the same reasons. There is a big hook in the end of the distillation curve with VP Red that raises the temperatures too high for our use. While this is a liability in these engines it can provide a useful cooling effect in a high strung two-stroke. It's clear from looking at the spec sheet that VP Red was designed for small block Chevys and similar type engines. In that application it's quite good.

You'll see the opposite effect with a fuel like C12. It is readily vaporized so a higher percentage of the fuel that passes through the jets ends up in the chamber in a usable form and it allows you to LEAN out the jetting.

There is a lot of really useful info in the spec sheets that fuel companies provide, it's just a matter of looking at them with your specific application in mind. :cry:

  • beezer

Posted October 26, 2004 - 10:29 AM


I think I'll just keep getting pump premium.

But I appreciate the information!

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  • bzakk

Posted October 26, 2004 - 02:32 PM


Thanks for all the info guys I am going to stop runnin 100 and start running 91 no use in wasting my money for nothing. :cry: :cry: :cry: :cry: :cry:

  • Scooter426

Posted October 26, 2004 - 03:56 PM


I was given a race gas mix formula for a gas that is very similar to power mist race gas (this was in the mid 1990s). It included 85% 100LL aviation fuel. The remaining 15% was made up of Xylene, Toluene, and Acetone. I still have this stuff in my garage. It worked quite well. I do not remember the exact mix ratios of the X,T and A, but I believe the mix called for no more than 5% Xylene. It was a 106 octane mix, I believe, for superbike racing engines. We were told not to go for high octanes, simply because they were for lower revving car dragster motors. The superbike motors were revving to 14K-15K at the time and were high compression motors. After that came oxygenated fuels they worked dramatically better. Almost like adding Nitro.

  • SFO

Posted October 26, 2004 - 05:36 PM


Almost like adding Nitro.

Nitro what?
Methane, propane? :cry:
RR must be bored to death to be cruising fuel posts on TT. :cry:

  • FFRacing79

Posted October 26, 2004 - 05:48 PM


SFO, what's up? I used to look forward to your informative they just seem...different. Just wondering???? Tdub

  • SFO

Posted October 26, 2004 - 07:04 PM


Tryce, you looked forward to my posts?
I never would have thought as much, but I appreciate your approval.
I can only imagine how hard you bust your butt to make Marks bike run right.
I was always grateful after pitting next to him that Doug was easy on equipment.
Sorry Tryce, just feel like I am turning into a surly old man.
Watching people rehash the same misinformation their guru local wrench taught them and cling to it in the face of reality seems like everything I loathe about the mc industry.
This is totaly not personal either, only for me.
i don't have the stomach to be a national wrench or a lifer mechanic.
I am just a wannabe who got to stand on a podium once.
I apologize for my indescretion.

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