Advice on Octane Boost for 2002 Yamaha WR250F

[ZekeWard]

Hello:

I just bought a new bike, it's a 2002 Yamaha WR250F, (and yes I
got it started..) and the owners manual calls for 95 octane gas, now all I see out there is super unleaded 93 octane, should I use 104+ Octane Boost ?...let me know what you guys think...

thanks
ZekeWard

 

[xrsforever]

Forget this mess. Buy VP Ultimate 4,96 oct gas,best fuel for most 4 strokes and affordable.Results will make you grin

 

[SirThumper]

You wont have any problems with 93 octane pump gas.

 

[ZekeWard]

Cool, thanks for the help..I wasn't sure what to do...

ZekeWard

 

[Rich Rohrich]

Yamaha is talking about 95 RON not 95 pump octane. RON is the way many European countries display the octane at the pump. The major US companies all have premium fuels that are at least 95 RON. Keep in mind the pump octane is RON+MON / 2 . There is usually a 7-10 point difference between RON and MON so if you do some quick math you'll see you're safe.

 

[Boozer]

i was wondering how such a high compression engine like the 250F (12.5:1) can run on such a low octane fuel without detonating. is it the design of the head? i'm asking because even the best auto engines like Hondas VTEC don't run their compression ratio that high.

 

[ZekeWard]

I guess i'll stay with a good grade premium gas, like Chevron, Shell, BP
to name a few.. I also bought my wife a 2003 TTR-225 it calls for "unleaded" gas, but will it hurt it to put premium in it also ?.. That way one can of gas does both our bikes.

thanks for all the help...
Zekeward

 

[MrLuckey]

Originally posted by ZekeWard
I also bought my wife a 2003 TTR-225 it calls for "unleaded" gas, but will it hurt it to put premium in it also ?..

Premium is unleaded.

 

[woodsy]

Yea Zeke you cant buy anything but unleaded anymore. Burn premium in your WR and you will be fine!! I never had a spark nock problem with mine as long as I stayed abve 87 octane (sometimes you cant dind the good stuff at 93)!!!
Premium is best for ALL of them!!! The slower burning charectoristics of premium gas is a plus for any internal combustion engine - think about it!!!
Woodsy

 

[Rich Rohrich]

Originally posted by woodsy
The slower burning charectoristics of premium gas is a plus for any internal combustion engine - think about it!!!

Whether a fuel is premium or regular has no specific influence on it's flame speed. A fuel's laminar flame speed is a function of chemistry (specifically H/C bonding) not octane rating . Even if premium DID burn slower why exactly would that be a benefit? THINK ABOUT IT :silly:

Fast combustion limits the time available for the building blocks of detonation to form up so slowing things down is rarely a benefit.

 

[ZekeWard]

"I also bought my wife a 2003 TTR-225 it calls for "unleaded" gas, but will it hurt it to put premium in it also ?.. That way one can of gas does both our bikes."

I think the above question got misunderstood, I really want to know if my wifes TTR225 calls for "unleaded gasoline" meaning 87 octane, will it hurt the motorcycle to use 93 octane in it. That way both our motorcycles could run the same fuel. or is 93 octane not a good idea in a TTR225 ?

Thanks
Zekeward

 

[Lobster]

Rich, I've been out of school for a good 10 years now, and all that alcohol couldn't be good for memory retention, but increasing the octane in a specific fuel acts to resist combustion from sources other than the spark plug(compression, hot spots, etc) making it more difficult to ignite.

Octane reduces the ability of the fuel mixture to ignite, but it's flame speed is the same rate as lower octane fuel?

I'm not doubting you, I'm asking for clarification.

 

[biglou]

Lobster-I think I can provide a simple explanation.  Rich can go into more detail and correct any mistakes here.  Octane is resistance to "auto"ignition, which is exascerbated by heat and compression.  The actual flame speed is a result of the fuel's chemical makeup, as noted by Rich:

A fuel's laminar flame speed is a function of chemistry (specifically H/C bonding) not octane rating .

 

[Rich Rohrich]

Originally posted by Lobster
but increasing the octane in a specific fuel acts to resist combustion from sources other than the spark plug(compression, hot spots, etc) making it more difficult to ignite.

No it doesn't. The willingness of a hydrocarbon based fuel to ignite is essentially a function of it's ability to vaporize. Once it's vaporized they ALL light off pretty much the same. The difference lies in the actual burning or more correctly the reaction that takes place. Chemical reactions speed up with high temperatures. The components in higher octane fuels are less likely to have weak molecular bonds that can break easily and form active radicals. Higher octane fuel is just made up of components that are (for lack of a better term) more stout under high temperatures and high cylinder pressures. Things like lead and metalic additives like MMT tend to work as an anti-catalyst and slow/blunt the formation of the active radicals that lead to auto-ignition of the fuel and detonation. The longer it takes to react all the fuel the greater the chances are that heat will accelerate the reactions beyond what the fuel components can bear. The idea that purposely SLOWING things down in the chamber is somehow beneficial in light of the reactions taking place is pretty funny really ;)

Heat , pressure, and time tend to be the driving force in all of this. The more heat and pressure you subject the fuel to and the longer you keep the temps elevated the better and more stable the fuel you need .

It's just simple chemistry really. If you look at the chemistry of explosives you can see a lot of similar reactions taking place, and it can give you some real insights into what's happening inside the combustion chamber when things go wrong.

 

[MrLuckey]

Originally posted by ZekeWard
[Bmy wifes TTR225 calls for "unleaded gasoline" meaning 87 octane, [/B]

"Unleaded gasoline" does not specifically mean 87 octane, it merely means just what the name says - 'unleaded gasoline' ie gasoline without LEAD.

Whether your local pump says 85 - Unleaded 87 Super - 89 Premium or whatever - those are ALL "unleaded gasolines"

 

[Lobster]

Sooo.....Excessive or abrupt pressure spikes coupled with localized heat before or during the combustion process can cause the fuels HC chain to break causing those evil active radicals. The active radicals can accelerate the combustion process by igniting, spiking pressure even more causing the hc chains to break down faster and produce more active radicals which in turn causes the fuel to burn faster than originally intended? Or worse lighting off on one side of the combustion chamber while the plug lights off the other side causing the flame fronts to collide and PING.

If I have a grasp on that, and the octane level makes the chain more stout, then what happens to the attached(?) octane molecules during the combustion?

I guess this is getting pretty deep as far as the original topic is concerned huh?

 

[JasonJ]

Is there any advantage to using higher octane fuel if the motor runs fine on lower octane? Gas manufactures claim increased performance and milage from additives but it seems they are aimed at fuel injectors. I have noticed differences in my bikes power and milage when using higher octane fuels wich seems to sugest higher energy density of the fuel, is this just BS? One time in particular that comes to mind on a street bike, I track my fuel by milage, and I usally use the highest octane available, I had to put 86 Octane in my bike since it was all that was available, and I ran out of gas well before I usally do mileage wise and it was all highway miles so I figured I would fair better not worse! Am I just nuts?

 

[Rich Rohrich]

Originally posted by JasonJ
Is there any advantage to using higher octane fuel if the motor runs fine on lower octane? Gas manufactures claim increased performance and milage from additives but it seems they are aimed at fuel injectors. I have noticed differences in my bikes power and milage when using higher octane fuels wich seems to sugest higher energy density of the fuel, is this just BS

With the big name fuels there is the chance that you'll find a bit less random junk (kerosene, naptha, sediment, etc) in their premium fuels. There is just as good a chance that you caught a fresher load of fuel one time and and older load the other and it reacted differently in your engine. The higher octane pump fuels often times contain additional oxygenates to boost octane which often times will account for a difference in mileage. Highly oxygenated fuels need more fuel to attain a chemically correct air fuel ratio, so mileage tends to suffer as a result.

 

[JasonJ]

Originally posted by Rich Rohrich


. Highly oxygenated fuels need more fuel to attain a chemically correct air fuel ratio, so mileage tends to suffer as a result.

I dont follow, is higher octane fuel more highly oxygenate? This last term seems to contradict what you said about higher octane haveing oxegenators and getting better milage or am I confused by the terms?

If higher octane fule gets better milage becuase it mixes better with oxegen than dose that not indicate a more even burn and better efficency and better performance?
In your opinion, how fast dose fuel degrade for instance in my plastic fuel tank. I have herd that keeping gas in your bike is a bad idea, but I often keep half a tank or so in my bike between rides of one month or so, if its been more than a month, I usally empty the tank into a can and dump it in the van.
Great info here, good reading, thanks for droping all the knowlage Rich!
This issue came up on another board where it was argued that lower octane was needed at higher elevations do to less oxegen density.

 

[Boozer]

QUOTE]Originally posted by Rich Rohrich

Highly oxygenated fuels need more fuel to attain a chemically correct air fuel ratio, so mileage tends to suffer as a result. [/QUOTE]

i am assuming that this only applies to EFI vehicles running a closed loop system. does it affect a carby fed motorbike running the original jetting? by that i mean if my bike is jetted correctly with one fuel, and i change to a different octane fuel, will my fuel consumption change because of what you said? unless the density of the fuel is different, isn't the same amount of fuel passing through the same size jet(s)? Please educate the un-educated proffessor!
Jason, is your street bike fuel injected?

 

[Rich Rohrich]

Originally posted by JasonJ


I dont follow, is higher octane fuel more highly oxygenate? This last term seems to contradict what you said about higher octane haveing oxegenators and getting better milage or am I confused by the terms?

With pump fuels it's a common practice to add additional oxygenate to attain a higher pump octane number. All else being pretty much equal the oxygenates have about 10-15% less energy (BTU/lb of fuel) than the base premium fuel. So, without correcting for the differences the engine runs a bit leaner and can conceivably make a bit less power (via overly lean jetting and lowered total energy) and have to use larger throttle openings riding the same areas which would tend to use more fuel . If you jet for the additional oxygen in the chamber by adding more fuel (either closed loop EFI or changing brass in a carb) you'll likely see a mileage decrease as well (more fuel flowing through the jets) but you'll also make additional power. Fuel efficiency and horsepower seem to be opposite sides of the same demon coin :p It can be tough to get one with out giving up the other.

If you are talking about non-oxygenated fuels, then changing from one pump grade to another shouldn't have much of an impact on economy either way. But pump fuel is totally unpreditable so your mileage may vary. (Pun intented :thumb: )

 

[JasonJ]

So it would behoove us to run the lowest octane we can in our bikes with out predetonation? I know here in Pa there was a whole debate about oxegated fuel, I tink they require it in the winter monts because of the hole in the O zone or someting, but every one coplained it made their car run like poo and it smells bad.
No my street bike is CVC carbs.
I know on my WR a few times I hve run low octane fuel I would get a rust color spooge ozing out of the carb and others have said the same thing, I just thought higher octane fuel was refined beter. Well, Im gonna stop using octane booster in my tank and see if it quits the popping and lean starting I have noticed since it got colder.

 

[Rich Rohrich]

Originally posted by JasonJ
So it would behoove us to run the lowest octane we can in our bikes with out predetonation.

NO if you are talking about pump fuel.

Here's some of my personal basic rules of thumb:

- ALL US pump fuel is TOTAL crap for use in a modern race bike. The degree of crappiness varies based on a ton of factors and vary from week to week so you'll never consistently pin them down
.
- Premium pump fuel from big name companies tends to be less crappy than the cheaper low octane stuff, so using low grade pump fuel is ASSININE IMHO.

- Pump fuels that use ethanol (alcohol) as their oxygenating agent will cause the most problems in terms of jetting, water absorption, and corrosion. Ethanol doped fuels have no business in a modern race bike.

- MTBE is not some chemical anti-christ that needs to be avoided. Regardless of what the local nit wit mechanic or knee jerk, failed out of all his science classes, clueless green freak might want to tell you.

- In almost every case 100ll Avgas is a better choice than current US alcohol based pump fuels

- Mixing 100LL Avgas with a good race gas designed for your application and rpm range is a reasonable way to save some money, and makes more sense then dumping crappy pump fuel into good race fuel.

- Mixing alcohol based pump fuels with ANYTHING in an attempt to make it BETTER is just a chemical circle jerk, and if you're that cheap or that ignorant you deserve the crummy performance and the insurmountable jetting problems that you will invariably be blessed with.


Here's some additional info on MTBE for those of you who have dozed off YET :confused:

AMA legal race fuels with MTBE generally contain about 15% by volume and subsequently have a lower energy per pound. You have to look at the big picture to see how this works in our favor.

Here's a few numbers to explain things :


Typical leaded race fuel (no oxygenates) = 18636 (BTU/lb)
Typical unleaded race fuel (with ~15% MTBE by vol) = 17876 (BTU/lb)
MTBE = 16353 (BTU/lb)

As you can see the addition of MTBE lowers the overall energy value. So on the surface it looks like the leaded race fuel with highery energy content would make more power. But we know it doesn't. HOW COME?

We have to look a little deeper and figure out the heat available in the cylinder per pound of air. If we look at the chemically correct (Stoichiometric Ratio) air/fuel ratio of our non-MTBE fuel we see it's 14.88 while the MTBE laced fuel has a Stoichiometric Ratio of 14.15 (for reference MTBE is 11.76) . So that tells us we need to add more fuel for each pound of air we ingest into the cylinder when we are using an MTBE based fuel. In this particualr example we would need to add 1.016 times more fuel with the MTBE based fuel (1.228 for pure MTBE).

So we have more fuel in the cylinder for each pound of air with our oxygenated fuel and the actual heat available in the cylinder per pound of air (or specific energy)looks like this:

Typical unleaded race fuel (~15% MTBE by vol) = 1263 BTU/lb of air
Typical leaded race fuel (no oxygenates) = 1252 BTU/lb of air

MTBE = 1391 BTU/lb of air

So as you can see even though the non-oxygenated fuel started with an advantage sitting in our fuel can once it got around to doing some real work it loses the race.

The super-fuels Nitromethane and Methanol have similar characteristics to our MTBE-fuel. Lower energy per pound but higher specific energy when you add in enough fuel to compensate for their lower stoichiometric ratios ( about 6.47 for Methanol and about 2.1 for Nitromethane). All that extra fuel adds up to lots of extra oomph.


In short, if you want to run pump fuel you are going to trade off some performance and response PERIOD. Whether or not that trade off is an issue is up to you decide.

 

[JasonJ]

Great info agian Rich, it seems the fuel equations are alot more dynamic that I for one whould have ever though. Trade off Smadeoff, in my dirt bike,,, I want MORE POWER!
I thought all av gas was leaded, is that not true?
My local Texaco sells some kind of VP race gas, Ill have to give that a tank load and see exactly what Im missing here useing 94 octane pump gas.
Well, hey look at it this way, at lest we dont have to mix oil with our gas anymore! :) LOL

 

[Rich Rohrich]

Originally posted by JasonJ
I thought all av gas was leaded, is that not true?

In the US AvGas is leaded, not sure about other places.

The lead content of AVGas (approx .56g/liter for 100LL) is still much lower than most leaded race fuels though.