95 octane


40 replies to this topic
  • yzf_guy

Posted December 30, 2005 - 09:35 PM

#1

Hey guys I am new to this forum and to dirt bikes. I ride quads, but I wanted to start ridding dirt bikes. My question is, do you have to run 95 octane or can you run 91. The guy at the shop said to put premium in. Premium to me is 91. 95 is race gas. Just wondering because my YFZ450 used 91, but the compression was 11.1 to 1 or somewere around there. thanks, Scott

  • kawirider

Posted December 30, 2005 - 09:41 PM

#2

Your premium is only 91? Mine is 93. We have been running 93 octane in my dads WR250F for about 8 months here on 4 year old valves with no problems. The guy I bought my 450 from said he has been putting 93 octane in it for the 3 years he has owned it, and the valves have stayed in spec. I would think that 91 would work just fine.

  • blue122

Posted December 30, 2005 - 09:54 PM

#3

I run 92 in my yz250f 2005 runs better than race gas and the guys at the race track all run 92 but race gas is ok if your motor is hopt up but stock run premium.

  • Fizz

Posted December 30, 2005 - 11:22 PM

#4

i run shell V-power in my 426 .. dont know if they sell it in the states, but its 99 octan ....

i think my engine deserves the best, and its no money to save there .. it uses so little fuel anyway ....

  • uplate

Posted December 30, 2005 - 11:40 PM

#5

I have a brief education on this.A friend I used to ride with was a chemist for Chevron. It has been some years so I'll be brief. The higher octane fuel will not make a motor faster or give it more power. It only serves to support the design of the motor. In other words if you have a real high compression engine you will need higher octane fuel to prevent detonation, pinging, or worse, a complete topend meltdown. Higher octane fuel actually burns slower and can reduce the power at higher rpms, especially with these high reving fourstrokes out now. My personal experience is from racing smokers with all that exaust (power valves) valve gadgetry, is that when I used pump gas the valves would get gummed up with carbon quickly. After swithing to a good quality race gas I could go for ages before the carbon buildup was noticeable. I believe the key is to use a good race gas but don't think that 114 octane is getting you anything extra, but maybe less. Stick with about a 100 octane for a long hard pull at high revs and a cleen topend. :applause:

  • crf-f crf-r trx cbr

Posted December 31, 2005 - 08:41 AM

#6

sunoco 94 ultra :applause:

  • Dieselhound

Posted December 31, 2005 - 09:02 AM

#7

What I do is run premium pump gas in my YZ450 and other high performance engines and then if the gas has gone a bit stale from storage, (and thus lost some octane), I mix some high octane race gas in with the Premium to bring the octane back up. One of my ultralight engines was really demanding of 91 octane and if the gas had sat unused in the tank for 3 week or more, it would diesel and detonate. To fix it, I would just add about 50% race gas and then problems solved. In summary, pump premium gas works if it is fresh but if it has sat and evaporated/oxidized for a month or more, then add some race gas. (I worked for UNOCAL science and technology making experimental gasoline for 5 years. ) As mentioned in a post above, if you run substantially more octane then needed, you will be losing money and possibly power.

  • BergArabia

Posted December 31, 2005 - 10:00 AM

#8

I only ever use premium gas in my YZ or my Vmax...
I go with the protects the engine but doesn't give more power explanation and that is fine by me.. :applause:

  • flintlock28

Posted December 31, 2005 - 11:40 AM

#9

This question has been asked a thousand times but here goes again......

If you are using a STOCK engine with standard compression, than you will only need to run 91 octane to about 94 octane (using (R+M)/2 method) This is one of the most popular methods of measuring octane at your local gas station.

With STOCK, don't go below 91 octane, or over 94

If you go less than 91 than you risk "pinging" or pre-detonation which will damage your pistons, and possibly melt a hole in the piston's top.

If you go over 94 octane (with STOCK engine), than you are wasting money, AND you will get slightly LESS power. Remember higher octane has less BTU's (British Thermal Units) than lower octane. In fact MX Action magazine stated this also.

IF you go to a higher compression piston than stock...THAN you will need to use a higher octane fuel to prevent pre-ignition.

Happy motoring....

  • flintlock28

Posted December 31, 2005 - 11:42 AM

#10

Hey DIESELHOUND,

What type of ULTRALIGHT Aircraft did you have??

I had an ISON Mini-Max with a Rotax 277 engine..

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Dieselhound

Posted December 31, 2005 - 03:22 PM

#11

Mine was a ppg trike with a Simonini 202 cc engine. Sorry for the off-topic post.

  • gary81

Posted January 01, 2006 - 04:28 AM

#12

Higher Octane Means More Fuel .the Higher The Octail The The Cooler The Burn.intern Means More Fuel Into The Combustion Chamber, Means Bigger Bang !!!!
Also Alot Cleaner Burn ,with A Better Fuel .
Thanks Its Been Wheely Nice !

  • Matty05

Posted January 01, 2006 - 05:08 AM

#13

Higher Octane Means More Fuel

It doesn't mean more fuel, it basically means more compression before spontaneously igniting. Flintlock28 is right :applause:

octane rating is the ammount of octane % in the fuel. (octane is a hydrocarbon with 8 carbons chained together, handles compression really awesome)

  • ovrrdrive

Posted January 01, 2006 - 05:54 AM

#14

Higher Octane Means More Fuel .the Higher The Octail The The Cooler The Burn.intern Means More Fuel Into The Combustion Chamber, Means Bigger Bang !!!!
Also Alot Cleaner Burn ,with A Better Fuel .
Thanks Its Been Wheely Nice !


That is one hell of a first post there m'boy :bonk:

Of course it's almost completely wrong, but hey what are these "facts" everyone keeps talking about around here anyway?

:applause:

Try searching...

  • kawirider

Posted January 01, 2006 - 10:48 AM

#15

So I guess what you guys are saying is that premium pump gas can sit for as much as a month and it will still be okay to run in my YZ??

  • grayracer513

Posted January 01, 2006 - 10:51 AM

#16

The higher octane fuel will not make a motor faster or give it more power. It only serves to support the design of the motor. In other words if you have a real high compression engine you will need higher octane fuel to prevent detonation, pinging, or worse, a complete topend meltdown.

Quite true

Higher octane fuel actually burns slower and can reduce the power at higher rpms, especially with these high reving fourstrokes out now.

Not true.

Higher Octane Means More Fuel .the Higher The Octail The The Cooler The Burn.intern Means More Fuel Into The Combustion Chamber, Means Bigger Bang !!!!

delerium

Stick with about a 100 octane for a long hard pull at high revs and a cleen topend. :applause:

You don't need 100 octane.

Where to start? First, yzf_guy, your YZ450 had a 12.5:1 compression ratio. The manual calls for fuel with a Reasearch Octane (RON) number of 95 or higher. For any given true octane value, RON will be a higher number than Motor Octane Number (MON). Most gas pumps I'm aware of use an average of the two, as flintlock pointed out (R+M/2). Thus, a posted pump octane of 91 or 92 is high enough, and works just fine if the fuel quality is good enough in general.

Here's the important part: Octane number is a value given to the ability of a fuel to resist being ignited by heat and pressure and that's all it tells you. Some fuels burn faster and some burn slower, but octane does not measure that. Some fuels have higher or lower BTU content, but this too is not something that the octane number tells you one way or other. All it does is to tell how well a fuel resists being ignited by anything other than a spark or open flame, which is the only thing that can be allowed to ignite the fuel within the engine. High octane fuel is not, simply as a function of its octane number, harder to ignite, faster, slower, hotter, or cooler burning, or more or less powerful than lower octane fuels. Those are all separate and independent characteristics of the fuel that are controlled by other things about the fuel's chemistry. Some high octane fuels may have one or more of these attributes compared to a given low octane fuel, but not because of it's octane.

Race gas is not 95 octane, or 114, or any other number, but whatever of all the various octane numbers it is available in for different applications. Some VP fuels are available at nearly 120 octane, but U4 is 92. High performance two-strokes need octanes over 100 quite often, but modern, high revving MX four-strokes don't, in spite of their very high compression ratios, and paying for more than what you need is a waste of time and money. Race gas produces more power simply because it's better fuel than pump gas, that's all.

Bottom line is that 90% of us with an MX four stroke will never need anything more than pump premium. That is not to say that some such fuels aren't better, or cleaner burning, or more stable, or give better performance than others, because some are. But the vast majority of them are quite adequate for most of us.

More on this subject:

http://www.faqs.org/...line-faq/part3/

  • Dieselhound

Posted January 01, 2006 - 11:27 AM

#17

GrayRacer is a truly informative guy and I would only like to add a couple of things: When a manufacturer says to run no less than 95 octane, they are not referring to the US method of measuring it. European 95 octane is frequently equivalent to US 91 octane because we average two different methods of measuring it and Euro uses only the one method. As pointed out earlier, the US uses Research+Motor divided by 2.
Many European and Asian countries only use the Reasearch method. A sample of gasoline might test out at 91 octane here and 95 octane in Euro.

For a little history on octane, when gasoline was first distilled from crude and used in engines, they needed a way to measure the resistance to pre-ignition. (ignition without spark). They chose pure ISO-octane, (which is an 8 carbon molecule) ran it in an engine with adjustable compression and assigned it a number of 100. From this they generated a scale. Any fuel testing worse than ISO-octane would be given a number less than 100 and any fuel testing better would be given a number higher.

In simple terms, the higher the number, the harder the fuel is to ignite.

One time in the lab, I made some fuel that was so high octane, (above 120, that my Hodaka wombat engine couldn't ignite it at all and wouldn't start.)

The test engines in the knock-lab could run it because they run real hot spark and wide spark gaps.

As a side note, some super-high compression race engines running on super high octane fuel need to run super big spark-plug gaps and a huge spark voltage/current just to ignite the stuff.

  • Dieselhound

Posted January 01, 2006 - 11:55 AM

#18

So I guess what you guys are saying is that premium pump gas can sit for as much as a month and it will still be okay to run in my YZ??


The best way to look at gasoline is to compare it with beer or soda. Left out, exposed to air and sunlight, it goes flat, loses it's fizz.
The soda has lost it's carbonation and the gas has lost it's light ends.

Light ends are the light molecules.

When gas loses its light molecules, it loses some of it's octane rating.

How quickly gas loses octane is related to how badly it is stored.

Worst case would be to put the gasoline in a clear plastic open container and leave it in the sun. It could go bad within days.

The sun's heat would evaporate the light ends and the UV rays would oxidize the remaining fuel.

As it oxidizes, it turns brown, much like a newspaper left in the sun.

If you have ever drained old gas out of a bike that was long in storage, you have seen the brown, oxidized gas. The octane of this crap would be below 80.

If gas is stored in a tightly sealed container and not exposed to sunlight or heat, it can last 3 or more months without losing much octane.

In average storage conditions, (plastic jug in someone's dark garage), I would give it 3 months, but in a motorcycle fuel tank with free-vent open, then I would give it less.

You can always drain the suspect fuel that it down a few octane and run it in you car or offer it to the poor teenager on your block.

I pour it in the miss's car when she isn't looking.

  • grayracer513

Posted January 01, 2006 - 12:26 PM

#19

In simple terms, the higher the number, the harder the fuel is to ignite.

Sorry, that's still wrong. 115 octane race gas is no more difficult to ignite with a spark than the cheapest regular 87 is, and in fact, it may be easier. What gives rise to this misconception is that some of the fuel components used to raise octane to very high levels, even though they will actually ignite fairly easily, will not continue to burn completely without a certain amount of heat support from the surrounding metals, or from compression. It's something like the gunpowder for high caliber rifles; packed behind a heavy bullet, it goes bang, but out in the open it will burn very slowly, and may not completely burn without the extra pressure and heat. But this, once again, is unrelated to the actual octane number of the fuel. A lot of car mechanics will experience this with customers burning summer blended premiums in low compression cars because they imagine it gives them more power. because of the fuel quality, the car will develop a "starts, but stalls immediately" symptom when the weather changes that is curable just by using winter blend regular.

I did mention the RON vs. MON vs. averaging question in my post, and the history of octane ratings is covered in detail in the link I posted.

  • holeshot

Posted January 01, 2006 - 01:24 PM

#20

My '00 426 owners manual called for 95 octane RON. The octane rating for gas at your local station is rated by RON + MON/2 (MON being the lower number), which translates to 91 or 92 octane at the pump in north America.

Just put the highest octane you can get at the pump and you'll be fine. If you're fanatical about things (and have lots of spare $), then there's nothing stopping you from trying race gas.





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