Race gas

I was wondering if anybody has heard about haveing problems running race gas in the blue beast. I have read that it was not a good idea beacuse of the harshness to the Carb seals. Also if there is a noticeable difference with the trick fuel or not. Right now i have been running 92 with octain booster in it.

Unless you hear detonation, you don't need higher octane fuel. It may actually be hurting the power. See discussion labeled "fuel information".

like he said don't run race fuel unless you need it to pervent pinging (detonation) you want to run the least octain you can get buy with. lower octain will produce more power in most cases .be sure to listen for pinging (pinging is very bad for your motor)if you hear pinging with the stock comp ratio 12.5 to 1 check your jetting you may be running to lean

I went to the mx track one day and forgot to buy gas, so I had to buy race gas at the track. I had a hell of a time with the bike dying on me when hot, and wouldn't start so save my life , I missed my second moto due to it dying on the line and they got 1 1/2 laps before the beast fired. My bike has always been a great starting bike, im sure it was due to not being jetted for race gas. The bike did run clean and throttle control was crisp but its runs strong on pump gas, I'm sure a pro can tell the differance with performance,but for me I'll put the $ 3.25 per gal. differece in my pocket and not in the tank.


Thanks for the info guys. I learn something new every day. So it is probably not worth running octain booster in the gas either?

My 426 would probably run on fermented and distilled coconut milk, if necessary (I hope Rich R. isn't reading this).

I've tried straight VP-C12, half pump/half C12 and just straight 92 octane, and haven't found a big difference for my style of riding, so I stick with 92 octane pump fuel.

This is not to say that there are no benefits running race gas (cooler operating temps, possibly), but you'll pull just as many holeshots with pump gas as race gas IMHO. But then again, I haven't tried every race fuel available.

I don't believe race gas will harm your YZF if you're inclined to experiment with different fuels (I'm sure Henry had race gas in his bike).

yzf wrote

lower octain will produce more power in most cases

Care to explain ? :)

Originally posted by Muroc:

yzf wrote Care to explain ? :)

Basically, octane rating is a measure of the fuel's resistance to detonation. Pure octane (a molecule consiting of an eight carbon atom chain with single bonds, surrounded by 18 hydrogen atoms, if I remember from chemistry) has an octane rating of 100. No magic, its just the standard. So that 92 octane you buy at the pump has 92% of the detonation resistance of pure octane. 110 octane rated fuel has 110% of that of pure octane. As you go up in elevation (like here in Colorado), the octane rating of the gas sold at the pump is less. The engines don't need the higher octane rated fuel to prevent detonation because the air is less dense up here. (Less oxygen molecules get sucked into the cylinder, hence our bikes don't put out the horsepower you sea-level guys get. Fortunately the 426 has plenty of HP to spare for a guy like me). I have been told by a reliable source (he helped develop the research octane number you hear about) that the lower octane rated fuels actually give off more energy when they burn. He says buying an octane rated fuel considerably in excess of what is needed to prevent detonation is counter-productive to developing maximum power. What high octane fuel lets you do is raise the engine's compression ratio without causing detonation (by milling the head or using a thinner head gasket, new piston, etc, probably why Doug Henrys bike used race gas). Higher compression engines make more power. Also, pump fuels are notoriously inconsistent, they are full of all kinds of additives and detergents. Just because one fuel says its 92 octane doesn't mean its the same formulation as another 92 octane rated fuel. My name is Mike, does that mean that I am the same person as any other Mike? The various effects you may see with different fuels may have nothing to do with octane rating. For example, oxygenating additives like MTBE and ethanol (mandated in various locales for pollution control) can cause problems regardless of octane rating. I avoid these fuels like the plague. I use pump gas, but I buy it in a nearby county that does not require that oxygenated fuel be sold in the pump. I have friends that run race gas in two strokes because they say it works better, my experience is that it runs richer. So if a bike is a little lean, it may help. Also, I bet the formulation is more consistent than pump gas, so I can imagine that you could get better results for that reason.

I don't think I have read or proven that excess octane will lower power. So I would be interested in the answer as well.

I'm definitely of the school that you only need as much as what is required to meet compression ratios, (or pressure differentiations…say in non-normally aspirated engines).

Keep in mind that with some engine management systems, power loss can occur when anti-denotation actions are taken, which result in lower power, (aka timing changes). This is why some autos will produce more power with higher-octane fuels.

92 pump seems to work well in the 426. In the auto-racing world, I know that race grade fuels, many of which are the same octane as pump fuels, as used for their consistency of quality. Critical for engine tuning and performance evaluations.

The other consideration with race gas is how much oxygenation has occurred with the product. This can produce a significant amount more horsepower (about 10%) if tuned properly. The VP MX3 blend is typical of this at slightly more than $25 per gallon. That may help in the hole-shot, but I really don’t think you would see any lower lap times unless you’re doing TT stuff.

That’s my two cents.


Originally posted by DaveJ:

I don't think I have read or proven that excess octane will lower power. So I would be interested in the answer as well.

I will talk to my friend and see what the BTU per liter rating is of the various pump fuels. He indicated that in general, there is less energy per amount of fuel in the higher octane fuels. I don't know if octane additives can dilute this ratio down or not, I'll try to find out. I don't know of any dirt bikes that have anti-knock sensors that retard timing like modern cars do, so it still seems that excess octane rated fuel is just a waste of money.

I appreciate the reply Mike, but it didn't really address the question. :)

lower octain will produce more power in most cases

I talked with my source and he gave me some off the cuff answers. It has been over twenty years since he worked for Gulf Oil so he cautioned that these answers may be dated.

Apparently, there isn't really all that much octane in pump gas. There is a wide range of hydrocarbons in it, the distillation process doesn't really need to be exact. They used to add benzene (a ring type hydrocarbon) to raise octane rating. That was found to be carcinogenic, so he thinks the oil companies use xylene instead (and that or some similar aromatic compound is what you are adding with octane booster). They can also strip off the hydrogen atoms on a hydrocarbon and make the single carbon-carbon bonds into double bonds to raise octane. He didn't say this, but I imagine there is less energy in these bonds, so when you burn the hydrocarbon with oxygen into H20, CO2, CO (and who knows what else, depending on your gas and jetting) you get less energy released between the two states. Therefore, there is less expansion of your gas charge and less power is generated by the engine. He also said that diesel fuel is a good example of a fuel with a low octane rating that has a much higher energy density than gasoline (a sparkplugless diesel engine ignites by detonation, the piston compresses the fuel until detonation fires the charge, hence a low (proper) octane rating is desirable). He also said that the trend of lower energy density with increasing octane is very slight and probably would not be noticeable in our case. But I do think that a lot of dirt bike guys confuse octane rating with energy density-they aren't at all the same thing.

I think you may be confusing the rate of burn with the issue of total energy produced. Not the same thing.

The only time you would see a decrease in horsepower using higher-octane fuels is when you don’t account for the slower burn rate with adjustments to ignition and/or cam timing. Which leads us to this:

Lower octane fuels have a tendency to self ignite under pressure and burn very fast and violently. Hence detonation, and in most cases severe damage to those components in the combustion chamber.

It's really an issue of total force applied against the top of the piston over the course of the power stroke. A slower smoother force against the piston will produce more “output” (or horsepower) via the crankshaft than a faster more sudden force, (assuming the absence of inertia involved in the piston and rod).

I think this is the same reason why a slower burning gun powder will fire a bullet further than a faster burning gun powder, even though total energy (area under the curve) is the same.



A little bit of common sense married to good science will lead us to a common denominator here. The YZ426 is a high revving engine with a fairly high compression ratio which would point to a good arguement for race fuel. Throwing out the cost factor(easy for me), what you end up with is, it beneficial or not. In my opinion, the good out weighs the bad. Actually, there is no "bad" if you don't consider the relatively high cost of race such as VP C-12. Race fuel won't hurt this bike, it can only "protect" it....to a degree. Racing applications subject an engine to severe loads throughout the RPM range. Race fuels can help protect, or slow, the detrimental effects of this use(abuse). A well matched race fuel makes good sense to me. I get Sunoco standard for about $4.40 a gallon here. If I subtract the cost of Exxon supreme at about $1.64 a gallon, the Sunoco isn't all that expensive...considering the other factors. It's not like I ride the 426 , 50 miles per day.So fuel economy is a non issue. My 2 cents.

[This message has been edited by Boit (edited 12-14-2000).]

I have been into Road-Racing for a while. both as a rider and mechanic.

What I found out there is the things to look for in a "race" gas....

The "octane" level is not the issue.

You have to pile up all in all:

Ron, Mon, made of Acetylate OR Mineral, how much oxygen it contains etc.

What You also need to consider is the fact that it carries oxygen!!! This means You have to put a bigger jet in Your carb.

You simply can not switch from pump- to race gas and do nothing with Your set-up.

Remeber this gas (especially Acetylate) is much cleaner and burns better.

This gives You less emissions and a cleaner and cooler engine !

The only setback is the money.

I think this is the same reason why a slower burning gun powder will fire a bullet further than a faster burning gun powder, even though total energy (area under the curve) is the same.

DaveJ, I have been sorting out my YZF for a HS so I didn't have time to respond. Per above,if the total (I assume you mean kinetic since you are talking about area under the curve) energy is the same between the two cases, there should be no difference in distance traveled, because the muzzle velocity will be the same. (The muzzle velocity will be the squareroot of two times the kinetic energy divided by the mass of the bullet). Since the kinetic energy at the muzzle can't be the same for a different distance traveled; there must be some inefficency somewhere in the burn process that delivers less kinetic energy to the bullet (hence a different area under the curve for the integral of pressure force with barrel length). Clearly not all the energy of the powder is transferred to the bullet; there is heat and friction, the sound, etc that take up some of the powder's energy. So there are ways for the faster burning powder to deliver less kinetic energy to the bullet. But this means a different area under the curve.

So I don't think that looking at the octane problem in terms of force on the piston provides much insight. One would need to have the piston force as a function of piston displacement to integrate for energy. Not easy. I suppose you could get this force function F(x) by placing a pressure transducer on the combustion chamber and recording the signal with an oscilloscope or data aquisition system.

If someone wanted to tackle this question analytically it would be best to use enthalpy relationships. Most thermodynamics texts cover this subject thoroughly.

The conservation of energy approach from fuel energy density (by looking at bond energies) provides an explanation to whether octane helps. I don't doubt that detonation will cause a problem, but I thought the premise was that the lower octane fuel was still sufficient to prevent detonation. Still, I agree with you that we really don't have a good answer to our original question.

How about this? There is a shop near my house that has a dyno, and the price is reasonable to run your bike on it. I am going to buy a 91 octane pump gas and a high octane race fuel. I will run my 426 on it with both fuels. To make sure that we account for proper jetting of the different fuels, we could run mainjets of 162, 158, and the next size down (152?). We can look at power delivered at full throttle as a function of main jet size for both fuels.

I get the added benefit of getting the ideal mainjet for my bike. Any suggestions for this experiment? What race gas should I use?


Wow...that's a lot of info.

So let’s agree on a few facts before we get too far into this.

So let's see. A higher-octane fuel will not produce any more "energy" than a lower octane fuel. Both fuels will basically produce the same amount of "heat" when ignited.

If a lower octane fuel causes an engine to detonate from compression, than "power" is lost, which can be gained back from going to a higher-octane fuel, which is more stable. Power, in this case, is lost because the early detonation is not the ideal moment for combustion to take place, (a similar effect would take place if you advanced your ignition timing).

And of course, damage is done to the piston when the fuel releases it's energy during the compression stroke - aka an opposing force.

If you had two similar engines, and both had very low compression ratios, and you ran one on high-octane fuel and the other on low octane fuel, both would have the same horsepower ratings.

Race gas, in low compression engines, will produce more horsepower because the fuel is oxygenated.

If you agree with all that, then we can get down to the issue of how "energy" can be optimally converted into "power".

Let me know and then we'll go back to the gunpowder - bullet analogy.


I don't think we can conclude that both fuels will generate the same amount of heat. It is possible that the lower octane fuel might lose more energy to heat, even if it had more energy density. If it burned faster and transfered more heat to the cylinder walls (because there was a greater temperature early in the cycle) I could see how it might develop less work and more heat. Presumably heat that stays in the gas causes the gas to expand and therefore is captured as work by the piston, while heat that is transfered to the walls just heats up your coolant. But it also seems like the cycle happens so fast that heat transfer shouldn't be that big an effect.

Also, here near Denver you can ONLY get oxygenated pump gas in the winter due to clean air mandates. But I have also heard that ethanol and MTBE (used here) can absorb water, corrode fuel systems, etc. I don't know if there is truth to these claims. Just to be safe, I have driven to a neighboring county to buy non-oxygenated fuel. I suppose I could be going to alot of trouble for nothing.

We can theorize till we are blue in the face, but I think it is going to be very hard to prove any benefits of race gas except by experiment. I feel like we are two kids debating who will win, the mongoose or the cobra. Lets put them in a pit and see who wins. What race gas do people feel makes the most difference in the 426? I am more than curious at this point, hell, if the race gas is better, I want to run it! On the other hand, if it is not, the dyno runs will eventually pay for themselves in lower fuel costs. Any other ideas on how to make the testing better?


If you want to see some significant result on the dyno, I can tell that you will be jetting up.

Oxygenated fuels needs bigger jets and will make more power.

I have my best results with Pro Racing Fuels, I did some test with pump gas,I had ELF, wicth was some better, and the MKII was a little superior to ELF. I din't have MKIV for that test, but on the track it's what feel the best in my 426.

Don't expect big difference on the dynojet type dyno, it doesn't load the engine long enough to really be a good test for the fuels.

In the US you can get Pro Racing Fuels from the guys that races jetski, or you can try the MR serie from VP for something quite close.


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