Race Gas or Super

Whichever fuel you guys decide to run, do yourself a favor and store it in glavanized metal containers....and try to keep the container at as a steady temperature as possible. Try to keep it in the shade while at the track. Fuels, whether pump gas or race fuels, are sensitive to UV rays and wide temperature changes. Race fuels are even more sensitive to UV rays. Properly stored race fuels have an almost indefinite shelf life while typical pump gas will "varnish" up in as little as 2 months.

SUNruh: What makes the VP Red the optimum fuel for the 426...and 250f? I mean, why is better than C-12 for these machines?

Actually SUNruh, I've never seen a crack pipe. If you would take the time to read instead of flap your lip you would see that I wrote of a MXA article that said to never run race gas in the 426... I could care less what you use...

I don't think you have to run race gas, but I do think it is more consistant than pump gas and easier to get the jetting straight. I'm using VP C-14 (with is what Rich recommended for the 426 SUnruh) and like it. But then again, what would I know....I'm so old and slow I could probably get good results running anything. At about $8.00 to $9.00/gallon its still cheaper than good bourbon!


I'm no gas guru but this is what I have been told. VP Red or 76 Red have the same specific gravity as premium unleaded gas. What this means is that it flows through the carb/jets the same way as pump gas allowing for minimal jetting changes.

I use 76 Red and have had to make minor jetting changes. The consistancy of the fuel is more important to me than the lead or octane issues but neither one of those hurt the bike either.

The issue is if you want to spend the extra $$$ for race gas.



i showed an ordered list with C18 being at the end. i then specifically said C18 was the best (VP Red being on the OTHER end).

looks like you MikeOK and Micheal just don't get it. never mind.

go back to the pump swill and jetting problems associated with it. have fun.

Cool SUnruh - an ordered list that runs in order of best fuels - right to left?? Guess I missed that calibration in the follow-on sentence. I "specifically said" I run only VP C-14.....I'm not sure which of us "doesn't get it!"

What's with the attitude???

This Hick learned something new today…

First off, MON is Motor Octane Number (not Measured, you dumbass Hick), the standard referred to in the manual is RON-95 (Research Octane Number, good guess you lucky Hick).

The MON index was designed to represent severe high-load conditions while the RON more accurately depicts everyday driving. When engine designers relied solely on the RON specification occasional knock-induced engine failures resulted. It was learned that not only was the RON spec. important, the MON had to be specified as well to account for how a fuel reacted to different operating conditions.

That is why the Antiknock Index in the US uses an average of the two.

The difference between the two ratings for any given fuel is called the “Octane Sensitivity” (RON-MON) and measures a fuel’s sensitivity to changes in operating conditions. Fuels with an overly high sensitivity may cause knocking despite a sufficient Antiknock Index value.

Because of this fuels in the US are supposedly held to a sensitivity of 10. If this is the case for the particular 91 Premium Unleaded you buy, this will mean it has RON of around 95 or 96.

“You truly should have known.”

Another golf clap for Hick. Your cool factor just went up a few more points! :) everyone else... "can't we all just get along?" :D


like a kid again!

00 YZ426F

01 TTR-125L (my son's)

91 CR125

83 YZ490

74 Hodaka Super Combat

Geez...I ask a simple question and.....

Oh well, now I know WHO not to ask anything.

Hey now - as you all know, the FBI scans all sites for sensitive key words, so using the words "crack pipe" could draw unwanted attention.



Holeshot's Page

If I remember correctly if it wasn't for pre ingnition the lowest octain available would produce more horsepower. The higher the octane the slower the fuel burns. Oh but remember I'm a dumbass half the time so don't qoute me on this it's just old school teachings. Jeff

I couldn't stay out of this one.

You're right, higher-octane fuels burn slower. This is why ignition maps (curves for the old guys) have to be modified when using some of this stuff.

And yes, lower octane fuels burn faster, but actually offer up less delivered power to the rear wheel, (long story). The lower octane stuff burns faster and more erratic, which is good for making bombs, but not of much benefit in a combustion chamber.

Lastly, you guys are inter-mixing the benfits of octane with oxygenation.

You can lose power from detonation as a result of running a fuel that is too low in octane, but if you exceed the octane for a particular compression ratio, you will not gain any more power.

However, you can gain power from a higher octane race fuel that has a higher level of oxygenation. Not because of the octane, but because of the oxygenation. Usually, the more expensive the race fuel, the higher the oxygenation.

Ok only half my a$$ is dumb.

Originally posted by DaveJ:

I couldn't stay out of this one.

You're right, higher-octane fuels burn slower. This is why ignition maps (curves for the old guys) have to be modified when using some of this stuff.

And yes, lower octane fuels burn faster, but actually offer up less delivered power to the rear wheel, (long story).

Sorry Dave, but now I can't stay out of this. It's a commonly held misconception that higher Octane fuel slows down the flame speed which keeps the engine from knocking. Flame speed is a function of fuel chemistry, NOT the Octane (AKI) rating. The fuel component Hydrogen/Carbon ratio along with the bonding of those components determines flame speed whether it's a high octane fuel or not. Racing fuels designed for very high rpm applications tend to have higher flame speeds than normal to help reduce burn time due to the short time available to react the fuel. High alkylate, very high octane fuels like Phillips B37 (AKI 118), and VPC2x tend to be some of the fastest burning fuels available to the average racer. Fuels that contain MTBE and/or ETBE (common race fuel oxygenates) also tend to exhibit shorter burn times as well as quicker initial pressure rise which allows the use of less ignition advance.

Except for the specialty fuels mentioned above there is virtually no difference in flame speeds for the majority of fuels that are commonly used. Again discounting specialty fuels and oxygen bearing components the available energy of common fuels when corrected for air/fuel ratio are virtually the same as well. No power differences will be realized purely from an octane standpoint.

We do seem to agree on the value of properly oxygenated fuels.

Well, whats the deal? straight up...race gas or pump gas? lets get right to the point without all the wordy explainations....does race gas perform better than super unleaded pump gas in a 400-426? If so, will the average rider notice a difference? yes or no? All the background info is interesting but only a few have given their opinion. Sorry, I hate to read between the lines...reminds me of dating.



Your not going to get the answer you looking for. " Is race gas better for the 426 or is pump gas fine?" What you define as better others will differ it's all opinion man. What might be better performance wise could be worse reliability wise and so on and so on. Some insist not using race gas is insane and isnt good for your bike others say it's way better for performance. I say we freakin possess the most wicked machines ever made and I aint going to notice a extra 2 hp gain, and with my freakin big gun exaust I sure in hell aint gonna hear pre detination so I'm gonna do what I've been doing the past 11 yrs,pull up to the gas pump buy a pepsi and hotdog go out and pump 92 in my bike drive out to the desert and unload it and ride the freakin thing as hard as I can.Then I'm gonna go back home and with the money I save from not buying race gas I'll order a pizza and drink beer till I fall asleep and do it all over again. Because I'm not intelligent enough to hang out with scientists and I'm not rich enough to stay at home all day researchin this stuff. Jeff

Originally posted by flyinguitars:

does race gas perform better than super unleaded pump gas in a 400-426?

If you choose the right fuel, then YES race fuel will outperform pump gas.

Originally posted by flyinguitars:

If so, will the average rider notice a difference? yes or no?

It's been my experience that the "average" rider lacks the willingness, skill, or time to jet a bike sharp enough to realize the advantages or race fuel, so the answer is probably no UNLESS you spend a lot of time running over 6000 rpm. At sustained high rpm the advantages will usually be realized even without proper tuning.

The REAL advantages of race fuel in these engines has more to do with throttle response than absolute power. I'm inclined to think that at least some of the problems with guys chasing the jetting has a lot to do with the fact that current US pump fuels don't like to vaporize. When you combine short intake tracts, short rod ratios, and high rpm like the YZ/WR has you have a distinctly different fuel requirement than the average EFI equipped auto engine. Food for thought. :)


[This message has been edited by Rich Rohrich (edited 03-14-2001).]


I can't compete with that.

However, you do have to admit (I hope) that if you stayed in the area of just pump fuel, or perhaps in the low end race fuels, that in general, the higher the octane number, the slower the fuel will burn.

I would have to assume that when you get into the higher tech race fuels that burn rate or propagation is going to be greatly effected by the oxygen in the fuel. Or some of the other stuff. Right? Isn't there a difference between how fast the molecules of fuel burn to that of how easily they ignite?

If that's not true, then it was not fair of me to make the general claim that I did.

By the way, it's my vote that supreme pump gas in these bikes is all your need.


Originally posted by DaveJ:


However, you do have to admit (I hope) that if you stayed in the area of just pump fuel, or perhaps in the low end race fuels, that in general, the higher the octane number, the slower the fuel will burn.

Sorry :) Flame speed is still just a matter of chemistry. But the good part is is a complete NON-issue unless you are working in the specialty ranges.

Octane rating is really nothing more than a measure of a fuels resistance to auto-ignition. It's probably worth mentioning that if you raise the temperature of any combustible mixture high enough, it will ignite on its own. This is sometimes called the "spontaneous combustion point" or the "auto ignition temperature". Knock is a rapid uncontrolled rise in cylinder pressure caused by all or part of the fuel mixture reaching this auto-ignition temperature.

The octane rating alone WON'T tell you anything about specific gravity, energy content (BTUs), flame speed, vapor pressure, or distillation curve. A lot of the stuff that has been written over the years has just made things more confusing.

If you guys have any interest I wrote a basic fuel article for Dirt Rider in 1985 (yeah I'm old) and I re-wrote it a few years ago for Eric Gorr's website. It's at http://www.ericgorr.com/techarticles/Fuel_Basics.htm

I did a glossary of Fuel Terms to go with it as well. http://www.ericgorr.com/techarticles/fuel_terminology.htm

Just so you guys don't think I EXPECT you to take my word for it here are some references on the subject

Harold H. Schobert - The Chemistry of Hydrocarbon Fuels - Butterworth-Heinemann Ltd.

Keith Owen, Trevor Coley - Automotive Fuels Reference Book - SAE - R151

H.P. Lenz - Mixture Formation in Spark-Ignition Engines - Springer-Verlag

Jeff Hartman - Fuel Injection - Motorbooks International

Germane, Wood, Hess - Lean Combustion in Spark-Ignited Internal Combustion Engines - A Review - SAE paper 831694

Z. Warhaft - An Introduction to Thermal Fluid Engineering - Cambridge University

and Dr. Robin Tuluie's excellent article at Motorcycle Online http://www.motorcycle.com/mo/mcnuts/rt-fuel1.html

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