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Race Gas vs. Pump Gas

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I have been running race gas mixed equally with pump gas and have lately been hearing that it is bad for my valves. And the i've even heard that just race gas is bad for it as well. Anyone out there know if it is just talk? Please lt me know

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is the race gas leaded? if so then that actually can be good for the valves, because of the cushioning properties of the lead.

is the race gas oxygenated? if so then the valves could be harmed if you do not jet properly. As I understand it, the Oxygenated race gas runs hotter.

I am running 50/50 leaded (non oxyenated) race gas (110 octane) and 92 premium pump gas.

good luck!

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Yo might want to rephrase that answer... My 64 Nova running 12.5:1 compression really likes leaded hi octane fuel, and its a 4 stroke....

Im jsut giving u a hard time....

Stock bikes reall ydont like race gas because it is to difficult to detnoate, if you get a after market ignition system then u should run a higher octane fuel though.....

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Is anyone running VP U-$ at altitude? If so, noticable HP gains? Are you running any hotter?

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There is a common misconception (not necessarily here at TT) that higher octane fuel somehow contains more potential energy, but (at least for normal, non-oxygenated gasolines), this is not the case. A higher octane fuel is more resistant to pre-detonation and burns more slowly when it is ignited, it does not contain more potential energy than lower octane fuels. In other words, the octane number describes how quickly the fuel will burn, not how much potential energy it contains.

In general, it's been my experience that for max power, you should run only enough octane to avoid pre-detonation. As you increase the octane rating past what's required to avoid pre-detonation (assuming fixed ignition timing, etc.), you not only increase the time after TDC at which maximum force is exerted on the piston, you also decrease actual maximum force on the piston. The result can be reduced power. Even though it's tempting to go high in octane, lower is sometimes better. I'd say the octane number given in the manual should be a good guideline 😢 .

As for damaging the valves, the lead content may be a benefit, but it's unclear to me.

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Fuel topics can be interesting. 4 strokes are a bit better tolerating the slow evaporating of the pump fuel making it a fair at best fuel for your thumper..

Octane is a can of worms and some posts here are very general in terms. Race fuel that is designed for a specific lil 4 banger is going to be very good for overall performance and not necessarily peak HP in all cases.

Octane is raised in some fuels by use of different components, these can help power or like posted hinder some power..maybe....I am not sold on octane robbing power..mismatched fuel for your application..yes.

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I run VP U-4, its only 92 octane and its oxygenated, and there is noticeable HP gains at sea level.

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Fuel is an interesting topic. Dyno testing has shown my CRF250R bone stock with opened airbox and M4 pipe gained .5 Horsepower going from Amoco Ultimate to VP's U-4. (We Had to do some jetting changes to get that?!) Some friends found that to get the full bennefit from Oxygenated fuel, timming needs to be changed which I have not done yet.

I was asking some questions of my engine builder which I have attached below, some of you may find this educational. 😢

I wrote:

With the new piston having 13.5:1 compression ratio I assume Amoco Ultimate 93 is out of the equation for normal use like practice days and Ice riding, but possibly not?

VP U4 has a low Octane rating; Motor Octane of 92. I know it is measured differently than standard pump gas, but not sure what type of knock resistance that has. In your experience is it enough octane to support 13.5:1 Compression ratio?

His reply:

The octane rating of the U4 is diffiult to compare to Amoco Ultimate as the Amoco uses the (R+M) /2 method of measurement. Rating the gasolines is a lot like buying computers, where a direct comparison is made intentionally difficult by the manufacturers. 😢 That is why we have over 15 different gasolines in stock. You often simply have to test,test,test.

Combustion chamber shape, cam profile and piston dome configuration all play into determining the octane requirements along with the usual ignition timing variable.

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The octane number does not describe how quickly the fuel will burn or how much potential energy it contains, etc. It just so happens that many higher octane fuels actually burn faster than lower octane fuels, but the flame speed itself is a function of chemistry and not octane. The term octane describes the grade of gasoline and its resistance to engine knock (automatically ignite) and the only time your engine is aware of octane is when it doesn't have enough. The total energy in BTU's for a given fuel can also be a misleading. A fuel rated with more BTU's may have more energy potential, but that doesn't mean it's all usable or usable within a certain range. The distillation curve defines the temperature at which various amounts of gas is vaporized. Generally, the race fuels for our motorcycles that offer more power with improved throttle response vaporize at lower temperatures and the distillation curve of a fuel can help clue you into good fuel choices.

Here's two excellent articles concerning fuel.

http://www.ericgorr.com/techarticles/Fuel_Basics.htm

http://www.ericgorr.com/techarticle...terminology.htm

There's a great deal of excellent fuel info here on TT If you do a search for "Rich_Rohrich" here on TT and read some of his pasts posts about fuel.

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4 strokes do not like high octane leaded fuel.

Mine loves it!

My 2 cents.

Stay away from oxygenated fuels unless you really know what you are doing, you will have to re jet and adjust timing.

Use higher octane race fuels to stop detonating, go too high and you may loose a very small amount of power and waste your money. 110 octane leaded works pretty well for me. Leaded race gas may help your motor last a little longer. If your running premium pump gas and have no detonation then racing gas is not necessary but has a neat smell 😢

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Mine loves it!

My 2 cents.

Stay away from oxygenated fuels unless you really know what you are doing, you will have to re jet and adjust timing.

Use higher octane race fuels to stop detonating, go too high and you may loose a very small amount of power and waste your money. 110 octane leaded works pretty well for me. Leaded race gas may help your motor last a little longer. If your running premium pump gas and have no detonation then racing gas is not necessary but has a neat smell🤣

You may think yours loves it. A stock bike w/stock jetting runs exceptionally well on VP- U-4, which is oxygenated. A stock bike with 110 octane leaded fuel is doing more harm then good to your motor. I'm just stating facts here, whoever told you to run that gas wants to see your bike run like crap for the little while longer it will be running. All this is from experience by the way, although 110 never entered my bike, but I've seen the aftermath personally. 😢😢😢😢😢

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You may think yours loves it. A stock bike w/stock jetting runs exceptionally well on VP- U-4, which is oxygenated. A stock bike with 110 octane leaded fuel is doing more harm then good to your motor. I'm just stating facts here, whoever told you to run that gas wants to see your bike run like crap for the little while longer it will be running. All this is from experience by the way, although 110 never entered my bike, but I've seen the aftermath personally. 😢😢😢😢😢

Just curious...

What aftermath? How can a cooler burning fuel that does not detonate cause harm to an engine?

Not flaming, just asking...

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I should restate my earlier assertion. There in no direct correlation between octane rating and flame front speed. A high octane fuel does not necessarily burn more slowly than a lower octane fuel. However, most leaded race fuels do often burn more slowly than most unleaded fuels. I may be mistaken, but I think that lead additives were originally developed to combat detonation by slowing the rate at which the fuel burned. More recently, octane has been increased by developing hydrocarbon chains that have the ability to withstand pre-flame conditions without decomposing and autoigniting before the flame-front arrives. Two good references on octane requirements, etc., are:

http://www.faqs.org/faqs/autos/gasoline-faq/part3/preamble.html

and

http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html

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Just curious...

What aftermath? How can a cooler burning fuel that does not detonate cause harm to an engine?

Not flaming, just asking...

From everything I've read the VP won't detonate, even though it makes your bike run leaner, you can get away with it and it won't detonate, now I'm not saying to run your bike lean, I'm just telling you what I know about the fuel. I don't know why the higher octane fuel causes damage to 4 strokes but it does, certainly a stock 4 stroke, maybe a modded race bike could be set up for it, but not a stocker, they say it does more harm then good. The aftermath I was speaking of was a bike that broke once a week, not neccesarily due to the gas but I'm just saying. 😢😢😢😢

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When I bought my bike the guys at Shanendoah Honda said they had done extensive dyno runs with gas from 87 octane to 120, the CRF250 had only a VERY slight HP gain with the $23 per gallon elf none oxygenated fuel. Everything else really had no significant gains what so ever.

For you guys that like to mix race fuel and pump gas, you get nothing more than the nice smell , But hey , if it makes you fell faster it must be worth it!! 😢

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