91 or 98 fuel?

[overworkedmonkey]

Guys,

Forgive me for my complete noobness and I know there are heaps of posts on the types of fuel however wanted to know if putting 91 or 98 fuel in the tank of a roadbike makes a difference. What about a mixture of fuel with ethanol? Apart from performance, is there any real benefit for putting in 98 in the tank?

[PirateJafa]

It'll make you "feel" faster. :facepalm:

[Corse1]

I go with 91 in both bikes. I notice no difference with 98. Can't see the point of paying extra for no gain. As long as the engine does not emit any "pinking" noise then from all the posts I have read on different forums the lower octane is better.

Lower octane requires less compression to ignite so is cleaner burning. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you should use. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the fuel for your engine costs more.

Using the lower octane may slightly increase fuel economy but I have never noticed the difference. You could argue that bike engines are all high performance motors so should usea higher octane.

Ethanol I avoid as I am suspicious on its effect when in contact with seals etc. I know that there is an issue with plastic fuel tanks expanding when using fuels with a high % of Ethanol.

[rastuscat]

Depends on your bike.

A BMW R1150GS sitting in my garage can run on fuel anywhere from 70 to 100 octane. The difference is the CAT plug in the ignition system. It's fuel injected, and the fuel mix can be varied. Different links in the CAT plug can vary the timing to cope with any octane rating. I get pinking if the octane is too low.

The reason is that around the world, from places like Uulan Bataar(Eastern Russia) to Dunedin, the octane rating of fuel varies so much, so the bikes are made to be able to cope. You just have to configure it to cope.

I guess you best check your manufacturer, as some are delicate. Mine isn't.

My car is one that needs high octane, but there are times when it isn't available. Like, there isn't 95 or 98 in Arthurs Pass, and if you need gas, you buy 91. I have been told that buying the higher octane actually increases your mileage, so despite costing more, it saves you money coz you use less. Might make sense.


It'll make you "feel" faster. Yeah, so does waxing your legs.

Anyway. Just my experience.

Donuts.

[Owl]

Where's the 95 option?:blink:

My bike specifies 95+ octane, so that's what I use. I've had to use 98 on the odd occasion, but to no advantage.

[Juzz976]

95 or 98 where available,

high compression motors need higher RON fuel.

the 91 95 & 98 figure is its relative resistance to knock compared to octane, not how much octane is in the fuel.

I occasionally use Force 10 from Gull, the ethanol absorbs moisture in your tank, then I go 4 a ride until its all gone and go back to 98/95.

[overworkedmonkey]

What would you recommend for a Honda CBR250RR? Tried doing a search but can't find anything specific. Whilst we are on the topic on fuel, what engine oil would you recommend? Any other suggestions would be welcome.

[MSTRS]

Rule of thumb is the higher performance an engine is, the higher the required octane petrol. I think the older, 250 performance bikes prefer 95/98.
Pinking occurs when too low an octane is used, and the engine is allowed to 'strain'. Either advance the timing or go to a higher octane.

As for oil, most 4 stroke motorcycle-specific oils should be ok. Mineral or semi-synthetic for a CBR250RR. 10-40 grade.

[SMOKEU]

What would you recommend for a Honda CBR250RR? Tried doing a search but can't find anything specific. Whilst we are on the topic on fuel, what engine oil would you recommend? Any other suggestions would be welcome.

My bike feels the same on 91 and on 98 octane fuel.

[superman]

My bike manual says 91+

Would never put in 91 though, the extra kms I get from a full tank of 95 compared to 91 actually makes 95 cheaper per kilometre. (at least in my bike... and in my car too) and I "feel" more power, though if it's just my imagination it doesn't matter because 95 is still cheaper.

Haven't tried a tank of 98 yet, because closest BP is about 30km away, Shell is only 10km away. So always just end up with 95. And that seems to work beautifully :yes:

[SMOKEU]

Would never put in 91 though, the extra kms I get from a full tank of 95 compared to 91 actually makes 95 cheaper per kilometre. (at least in my bike... and in my car too) and I "feel" more power, though if it's just my imagination it doesn't matter because 95 is still cheaper.



An engine usually produces more power on lower octane fuels because it burns faster than higher octane fuels. The exception is engines with knock sensors which change the ECU mapping when it senses detonation.

Running a nanna spec Corolla on 98 octane fuel is likely to produce less power than if it was running on 91 octane fuel.

[superman]

An engine usually produces more power on lower octane fuels because it burns faster than higher octane fuels. The exception is engines with knock sensors which change the ECU mapping when it senses detonation.

Running a nanna spec Corolla on 98 octane fuel is likely to produce less power than if it was running on 91 octane fuel.

Burning faster doesn't mean more power though, but I guess the more likely ignitions take place the more constant the power is. The higher octane just stops rogue detonations happening since lower octanes can cause ignition through compression. Granted the difference in 7 RON isn't necessarily that large.

[steve_t]

An engine will make the most power for the fuel it is tuned for. Engines with knock sensors can advance timing to get more power until they detect knock. If the engine can advance its timing sufficiently to take advantage of a higher octane's ability to prevent knock, this will yield the most power. Higher octane fuels usually have a higher energy content per litre

[Juzz976]

So whats the RON rating of a fuel got to do with how fast it burns?

Without knowing what the fuel mixture is made of you can't make any assumptions, the only time you can say for certain lower RON will burn sooner is where ignition starts from pre-detonation not from spark.

Even the way the fuel is dispersed from the injector/jets can be dramatically changed by the additives contained in the solution even in very low concerntrations.

Flame propagation is also affected by the fuels additives, temperature, mixture ratio and pressure.

[p.dath]

What would you recommend for a Honda CBR250RR? Tried doing a search but can't find anything specific. Whilst we are on the topic on fuel, what engine oil would you recommend? Any other suggestions would be welcome.

Being an older bike with no EFI, stick with 91.

[Edbear]

An engine will make the most power for the fuel it is tuned for. Engines with knock sensors can advance timing to get more power until they detect knock. If the engine can advance its timing sufficiently to take advantage of a higher octane's ability to prevent knock, this will yield the most power. Higher octane fuels usually have a higher energy content per litre

Pretty much. It depends on what the vehicle is tuned for. Modern fuel injected motors compensate for different octane ratings and may or may not benefit from the higher. My C50T definitely seems to run better on 98 and in particular Gull's 98 blend so I use that whenever I can source it.

Unless your bike is tuned for it, probably better to go with 91. Our Nissan Pulsar also seems to run better on 98, but it's hard to tell for sure without doing a dyno test.

[YellowDog]

My bike manual says 91+

Would never put in 91 though, the extra kms I get from a full tank of 95 compared to 91 actually makes 95 cheaper per kilometre. (at least in my bike... and in my car too) and I "feel" more power, though if it's just my imagination it doesn't matter because 95 is still cheaper.

Haven't tried a tank of 98 yet, because closest BP is about 30km away, Shell is only 10km away. So always just end up with 95. And that seems to work beautifully :yes:

I agree. My bike goes about 9%-12% further on 95.

[Juzz976]

you can get 95 RON with less octane than 91 RON and the other way around.

we use RON in NZ as a standard as it does not indicate how much energy is in each litre or how quickly it will burn or even how much octane is in it.

Just how much compression it can handle without detonation compared to 100 percent octane, this is why you can get 120 RON fuel and you cannot have 1200ml of octane in 1L of fuel.

Why? so you don't buy fuel that has a high amount of octane but additives which will cause detonation at lower pressures.

[overworkedmonkey]

Quite a fair bit of info to take it. So should I stick with 91 or 98?

[SMOKEU]

Quite a fair bit of info to take it. So should I stick with 91 or 98?

If it runs fine on 91 and doesn't detonate then use 91, unless higher octane fuels make it run better or give significantly better fuel economy.

[vifferman]

I go with 91 in both bikes. I notice no difference with 98. Can't see the point of paying extra for no gain. As long as the engine does not emit any "pinking" noise then from all the posts I have read on different forums the lower octane is better.
I run 91 in winter, and alternate 91 and 98 in summer, as the VFR pinks in hot weather, especially when the fuel level's low and the pump (which is in the tank) and the engine heat it up.
I avoid running any brand of 95/96 in any vehicle, as there's too much toluene/xylene in it. It sooted up the plugs in my VFR750, and the wife's Peugeot pinks when running it, but is fine on 98, which is refined in Orstrylyer and is better fuel than our high octane crap.

[overworkedmonkey]

If it runs fine on 91 and doesn't detonate then use 91, unless higher octane fuels make it run better or give significantly better fuel economy.

When you say 'detonate' you mean? How would I know it doesn't 'detonate'? How would I measure a better run? Would that mean a greater distance? Also how do I know it isn't damaging the engine as such? Remember owning a BMW and was advised by the mechanics to use 98 as anything lower would damage the engine.

[overworkedmonkey]

I run 91 in winter, and alternate 91 and 98 in summer, as the VFR pinks in hot weather, especially when the fuel level's low and the pump (which is in the tank) and the engine heat it up.
I avoid running any brand of 95/96 in any vehicle, as there's too much toluene/xylene in it. It sooted up the plugs in my VFR750, and the wife's Peugeot pinks when running it, but is fine on 98, which is refined in Orstrylyer and is better fuel than our high octane crap.

Utterly lost and confused by the term 'pink'. What does it mean? How do I know it's occurring?

When you say you avoid running any brand of 95/98? What does that mean? A particular provider e.g. Shell, Gull, BP, etc

[vtec]

What would you recommend for a Honda CBR250RR? Tried doing a search but can't find anything specific. Whilst we are on the topic on fuel, what engine oil would you recommend? Any other suggestions would be welcome.

I raced my CBR250RR's on 91 octane. They ran noticeably better on the lower octane gas. From idle right through to redline. Amazing little bikes. I've won races on Taupo, Manfeild, Philip Island, Broadford on CBR250RR's with 91 octane in them. It's cheaper and they got better gas mileage too. Mine were all Jap imports too.

Pinking is onomatopoeia I believe for the noise that the engine makes when a cylinder's mix explodes before the spark plug fires and far enough before the piston reaches top dead centre that it tries to push it backwards for a little bit, thus you get a massive skyrocketing of pressure in the cylinder trying to push it backwards if only for an instant, I imagine it's quite stressful.

[overworkedmonkey]

you can get 95 RON with less octane than 91 RON and the other way around.

we use RON in NZ as a standard as it does not indicate how much energy is in each litre or how quickly it will burn or even how much octane is in it.

Just how much compression it can handle without detonation compared to 100 percent octane, this is why you can get 120 RON fuel and you cannot have 1200ml of octane in 1L of fuel.

Why? so you don't buy fuel that has a high amount of octane but additives which will cause detonation at lower pressures.

Completely lost me there. Considering I'm a complete noob to petrol, additives, compression, etc, can you explain what you mean followed by examples. Am trying to learn as much as I can.

[overworkedmonkey]

I raced my CBR250RR's on 91 octane. They ran noticeably better on the lower octane gas. From idle right through to redline. Amazing little bikes. I've won races on Taupo, Manfeild, Philip Island, Broadford on CBR250RR's with 91 octane in them. It's cheaper and they got better gas mileage too. Mine were all Jap imports too.

Pinking is onomatopoeia I believe for the noise that the engine makes when a cylinder's mix explodes before the spark plug fires and far enough before the piston reaches top dead centre that it tries to push it backwards for a little bit, thus you get a massive skyrocketing of pressure in the cylinder trying to push it backwards if only for an instant, I imagine it's quite stressful.

Why do you refer to 91 octane specifically? Is there a difference between 91 and 91 octane? Sweet. Good to know that they are mean bikes to ride.

So I presume the sounding being quite loud. When would I hear the noise? When you say cylinder's mix you mean? I know nothing about mechanics yet so forgive my ignorance. Keen to learn.

[SMOKEU]

I raced my CBR250RR's on 91 octane. They ran noticeably better on the lower octane gas. From idle right through to redline. Amazing little bikes. I've won races on Taupo, Manfeild, Philip Island, Broadford on CBR250RR's with 91 octane in them. It's cheaper and they got better gas mileage too. Mine were all Jap imports too.

Pinking is onomatopoeia I believe for the noise that the engine makes when a cylinder's mix explodes before the spark plug fires and far enough before the piston reaches top dead centre that it tries to push it backwards for a little bit, thus you get a massive skyrocketing of pressure in the cylinder trying to push it backwards if only for an instant, I imagine it's quite stressful.

I haven't noticed any difference on my CBR if I run 91 or 98. It runs mint on 91, and it doesn't sound like it detonates on 91 so I just use that to save cash.

[overworkedmonkey]

I haven't noticed any difference on my CBR if I run 91 or 98. It runs mint on 91, and it doesn't sound like it detonates on 91 so I just use that to save cash.

SMOKEU, would you mind explaining detonation or the sound of what a detonation sounds like? Maybe a Youtube video with the sound?

[EJK]

Put diesel.


It's cheaper.

[Dave-]

higher octane is more stable, so you can advance the spark further.

the end.

[Flip]

IMHO the fuels we get here in NZ are crap, and the fuel regulations have been written by the fuel industry so they can supply any old shit from any where in the world. The fuel barrons throw all the terminal flushings into 91 and the 95 can sit around for so long it is often out of specification by the time you get it, thats if it was to start with.

Pinking sounds like a hand full of marbles in an empty tin can being shaken very hard. I agree with Smokeu on this one, and thats a first. Pinking is preignition of the mixture under compression and is very very bad for a petrol motor. The octane rating is the ability of the fuel not to do this and is found by laboratory testing in test motors. Pinking is the sound of the burning fuel being compressed and the pressure and temperature reaching levels that are damaging your motor.

It amazes me how many people think octane and calorific value is the same thing. Octane is the fuels ability not to ignite under compression, thats all, however as the octane goes up the flame front speed of the fuel drops. Taken to the extreme if you run race gas in a low compression vintage motor the fuel burns too slow and is still burning as it leaves the cylinder and heats up the exhaust because of the radiant energy from the still burning fuel.

The calorific value of 91,95 and 98 is almost exactly the same, they are so close it is impossible to distinguish them from each other by any practical laboratory calorific method.

Some motors have a pinking sensor, my Harley hasa sensor in the rear (hotter) cylinder head that detects the ultrasonic noise of the preignition and backs off the ignition. I am not sure how many other bikes would have this but I doubt a 250 would.

I haven't ever noticed any difference between any of the fuels available here in any of my bikes, I just buy what ever is cheapest and use the money to wear out more tires.

[SMOKEU]

SMOKEU, would you mind explaining detonation or the sound of what a detonation sounds like? Maybe a Youtube video with the sound?

I don't know much about engines, but what I can tell you is that a diesel engine does not have spark plugs. A diesel engine relies on the heat from the compressed air to ignite the fuel - a diesel engine compresses air inside the cylinders to an extremely high temperature before injecting fuel into the engine, and the heat from all the compression ignites the fuel. As you compress air, it heats up.

A petrol engine relies on spark plugs to ignite the air/fuel mix. No spark = no go. Detonation/pinking/pinging/dieseling usually occurs when the heat of the compression ignites the fuel before the spark plugs get a chance to ignite it. This is extremely undesirable in a petrol engine, and often leads to temperatures inside the engine to far exceed the design limits of the engine. In bad cases, this can result in melted pistons.

Detonation can occur due to using a fuel octane which is too low, therefore burning from the heat of the compression. It can also occur due to excessive intake temperatures, which may result from high boost pressures or inadequate intercooling in the case of engines which have forced induction. Incorrect valve timing can also cause detonation.

[SMOKEU]

I agree with Smokeu on this one, and thats a first.

There's a first time for everything.

[overworkedmonkey]

IMHO the fuels we get here in NZ are crap, and the fuel regulations have been written by the fuel industry so they can supply any old shit from any where in the world. The fuel barrons throw all the terminal flushings into 91 and the 95 can sit around for so long it is often out of specification by the time you get it, thats if it was to start with.

Pinking sounds like a hand full of marbles in an empty tin can being shaken very hard. I agree with Smokeu on this one, and thats a first. Pinking is preignition of the mixture under compression and is very very bad for a petrol motor. The octane rating is the ability of the fuel not to do this and is found by laboratory testing in test motors. Pinking is the sound of the burning fuel being compressed and the pressure and temperature reaching levels that are damaging your motor.

It amazes me how many people think octane and calorific value is the same thing. Octane is the fuels ability not to ignite under compression, thats all, however as the octane goes up the flame front speed of the fuel drops. Taken to the extreme if you run race gas in a low compression vintage motor the fuel burns too slow and is still burning as it leaves the cylinder and heats up the exhaust because of the radiant energy from the still burning fuel.

The calorific value of 91,95 and 98 is almost exactly the same, they are so close it is impossible to distinguish them from each other by any practical laboratory calorific method.

Some motors have a pinking sensor, my Harley hasa sensor in the rear (hotter) cylinder head that detects the ultrasonic noise of the preignition and backs off the ignition. I am not sure how many other bikes would have this but I doubt a 250 would.

I haven't ever noticed any difference between any of the fuels available here in any of my bikes, I just buy what ever is cheapest and use the money to wear out more tires.

Thanks Flip.

#1 When you say compression, what compression are you referring to?

#2 Does fuelling with a higher octane value mean that the fuel will not ignite under compression? Does also mean I should stick with 95 or 98?

#3 First time I have heard of calorific value. Never seen it mentioned anywhere at the fuel pump.



I don't know much about engines, but what I can tell you is that a diesel engine does not have spark plugs. A diesel engine relies on the heat from the compressed air to ignite the fuel - a diesel engine compresses air inside the cylinders to an extremely high temperature before injecting fuel into the engine, and the heat from all the compression ignites the fuel. As you compress air, it heats up.

A petrol engine relies on spark plugs to ignite the air/fuel mix. No spark = no go. Detonation/pinking/pinging/dieseling usually occurs when the heat of the compression ignites the fuel before the spark plugs get a chance to ignite it. This is extremely undesirable in a petrol engine, and often leads to temperatures inside the engine to far exceed the design limits of the engine. In bad cases, this can result in melted pistons.

Detonation can occur due to using a fuel octane which is too low, therefore burning from the heat of the compression. It can also occur due to excessive intake temperatures, which may result from high boost pressures or inadequate intercooling in the case of engines which have forced induction. Incorrect valve timing can also cause detonation.

Thanks SMOKEU. You mention that pinking occurs when ther heat of the compression ignites the fuel before the spark plugs do. How would you avoid this?

Now you also mention that detonation occurs when the fuel octane is too low. That does mean that we should always stick to higher octane fuel.

When do high boost pressures occur as well as inadequate cooling? What's forced induction?

[SMOKEU]

Thanks SMOKEU. You mention that pinking occurs when ther heat of the compression ignites the fuel before the spark plugs do. How would you avoid this?

Now you also mention that detonation occurs when the fuel octane is too low. That does mean that we should always stick to higher octane fuel.

When do high boost pressures occur as well as inadequate cooling? What's forced induction?

1. Don't run a WRX on 91 octane fuel.

2. Same as number 1.

3. Turbo/supercharger.

[overworkedmonkey]

1. Don't run a WRX on 91 octane fuel.

2. Same as number 1.

3. Turbo/supercharger.

Take that these don't apply to a CBRR 250 and 91 octane would be safe to use.

[dipshit]

#3 First time I have heard of calorific value. Never seen it mentioned anywhere at the fuel pump.

It's similar to 'British thermal units' ( BTU )

[SMOKEU]

Take that these don't apply to a CBRR 250 and 91 octane would be safe to use.

Exactly. If a CBR250 runs fine on 91 octane fuel, and does not make any funny noises compared to if you were running 95/98, then use 91.

[dipshit]

however as the octane goes up the flame front speed of the fuel drops.

Do you have any references to back that up..??

There are some that say that this is a widespread misconception and in fact octane levels and flame front propagation speeds aren't related.

[Toaster]

My bike feels the same on 91 and on 98 octane fuel.

Try aircraft AVGAS. WOOHOO!

Or a Y2K bike :innocent:

[overworkedmonkey]

Exactly. If a CBR250 runs fine on 91 octane fuel, and does not make any funny noises compared to if you were running 95/98, then use 91.

Sweet. I take it the sound will be audible enough for me to know. Now if it does start making noises, would I need to drain the tank? I also take it 91 does not include an ethanol mix.

[MSTRS]

All this fecking stress and angst over octane.
V-tec already told you...he ran 91 in his CBR250RR race bike, and had excellent results. What more do you need to know?

As for ethanol - I believe Gull is the only servo with it present in their petrol. Some vehicles are not recommended to use their Force 10 (10% ethanol) but only because of possible damage to rubber seals in the fuel system. If you can't be sure - just don't use Gull.

[overworkedmonkey]

All this fecking stress and angst over octane.
V-tec already told you...he ran 91 in his CBR250RR race bike, and had excellent results. What more do you need to know?

As for ethanol - I believe Gull is the only servo with it present in their petrol. Some vehicles are not recommended to use their Force 10 (10% ethanol) but only because of possible damage to rubber seals in the fuel system. If you can't be sure - just don't use Gull.

No stress mate. None at all. It's good to know what works and doesn't as well as the reasons behind it. I am not one to follow blindly without asking questions and along the way I have learnt heaps.

[SMOKEU]

I've heard from many CBR250 owners who say their bikes have more power on 91 than 98 so stick with 91. You might as well try 91 and 98 and see what works best for your bike.

[overworkedmonkey]

I've heard from many CBR250 owners who say their bikes have more power on 91 than 98 so stick with 91. You might as well try 91 and 98 and see what works best for your bike.

Thanks SMOKEU. Will give it a go and will keep the forum posted with the results.

[vifferman]

Rather than answer your many questions about things like calorific value, octane, etc., why don't you use Google? The answers are out there.
But while I'm here, the calorific value refers to the amount of energy produced when something is burned. This is done in a controlled (laboratory) environment (as is working out the octane rating). The calories (now kilojoules) are the same thing you see on food packets, and the test is the same: a measure quantity of food (or fuel) is burned in a special device called a bomb calorimeter and the heat produced is measured, maths is applied, and the result is a figure in calories (imperial) or kilojoules (metric).

one thing you won't find (but some replies to this thread have answered it) is about why not to use 95/96 petrol. It's because the Big4 petrol companies here own and run the refinery. In the process of refining the oil into various products, they end up with some that are of limited usefulness, like xylene, tolunene, etc. Some of this can be used for the manufacturing process of paints, plastics, etc., and the rest the bung in our fuel, a relatively cheap and shitty way to boost the octane rating. Too much toluene, xylene etc. leads to sooty engines, and nasty carcinogenic fumes (mind you, petrol is carcnogenic anyway). The octane rating in simplistic terms is the measure of a flammable substance's propensity to 'knock' or ignite before you really want it to, in a relatively uncontrolled manner. This pre-ignition causes the engine to make a knocking sound, also called pinking. This is really bad for the engine.

[Ocean1]

The octane rating in simplistic terms is the measure of a flammable substance's propensity to 'knock'

:yes: I once bought one of the very few knock rate test engines in the country, had adjustable fookin' everything. Inneresting to play with but I never found a commercial use for it and i think eventually the scrap dude got it.

[overworkedmonkey]

Rather than answer your many questions about things like calorific value, octane, etc., why don't you use Google? The answers are out there.
But while I'm here, the calorific value refers to the amount of energy produced when something is burned. This is done in a controlled (laboratory) environment (as is working out the octane rating). The calories (now kilojoules) are the same thing you see on food packets, and the test is the same: a measure quantity of food (or fuel) is burned in a special device called a bomb calorimeter and the heat produced is measured, maths is applied, and the result is a figure in calories (imperial) or kilojoules (metric).

one thing you won't find (but some replies to this thread have answered it) is about why not to use 95/96 petrol. It's because the Big4 petrol companies here own and run the refinery. In the process of refining the oil into various products, they end up with some that are of limited usefulness, like xylene, tolunene, etc. Some of this can be used for the manufacturing process of paints, plastics, etc., and the rest the bung in our fuel, a relatively cheap and shitty way to boost the octane rating. Too much toluene, xylene etc. leads to sooty engines, and nasty carcinogenic fumes (mind you, petrol is carcnogenic anyway). The octane rating in simplistic terms is the measure of a flammable substance's propensity to 'knock' or ignite before you really want it to, in a relatively uncontrolled manner. This pre-ignition causes the engine to make a knocking sound, also called pinking. This is really bad for the engine.

Thanks Vifferman. Did Google some of the queries I had however have no idea how the relate to a CBRR 250. Based on what you are suggesting is I should stay away from 95/96 and I assume that 91/98 are absolutely fine. Some have also suggested I stay away from ethanol blendings as the rubber seals may disintegrate. I also take it that the higher the octane rating, the lower the propensity for it to pre-ignite. Now seeing that I have picked up along the way with the many questions I have, a CBRR250 would have to have its spark plugs ignite the fuel and it is a possibility that a lower octane fuel like 91 MAY pre-ignite however based on the many suggestions, 91 is safe to use to elongate the life of the bike. Please feel free to correct me.

[MSTRS]

And still it goes on....
FFS - a CBR250RR is not something special (well, perhaps, but you should know what I mean) when compared to any/all other bikes.
The best advise as always is to use the lowest octane fuel your engine is happy with. V-Tec raced very successfully on 91. In fact, Japanese engines have been designed to use low/er octane unleaded petrol since well before your bike was built.
Some suggest that they get more distance out of a tank of 98, offsetting the extra per-litre price. This is anedotal, rather than scientific. Whatever, it is unlikely to cause any issues.
You choose. 91 or 98. The thing about 91 is that every gassy has it.

[Phreak]

I've used 91, 95, and 98 in my CBR250RR, with no noticable difference at all. I talked to some guys in Australia (Honda JDM CBR forums) (http://cbr250.com/forum/forum-4.html) about it, and they reckon that 98 will create more carbon deposits, whilst 91 and 95 are both fine. So I use 91 when I pull into a gas station that has 91 or 98, and 95 when that's available. IIRC, when I used to work at a gas station, 95 has better properties to prevent knocking, but I don't know that much about it.

End of the day, my preference is 95. Plus, the mobil just up the road from me at the moment has the best prices on gas that I've seen on the whole North Shore, so that makes the decision easy - for 95, that is.

One thing to take into consideration is though, what gas was your bike last tuned on...? Being a carby engine, if it was tuned on 91, it'll probably run best on 91, don't you think?

[overworkedmonkey]

I've used 91, 95, and 98 in my CBR250RR, with no noticable difference at all. I talked to some guys in Australia (Honda JDM CBR forums) (http://cbr250.com/forum/forum-4.html) about it, and they reckon that 98 will create more carbon deposits, whilst 91 and 95 are both fine. So I use 91 when I pull into a gas station that has 91 or 98, and 95 when that's available. IIRC, when I used to work at a gas station, 95 has better properties to prevent knocking, but I don't know that much about it.

End of the day, my preference is 95. Plus, the mobil just up the road from me at the moment has the best prices on gas that I've seen on the whole North Shore, so that makes the decision easy - for 95, that is.

One thing to take into consideration is though, what gas was your bike last tuned on...? Being a carby engine, if it was tuned on 91, it'll probably run best on 91, don't you think?

Thanks mate. Good to know what works best. Seeing that I don't know what it was last tuned on, is there a way to find out? I'll give each of the different fuels a go however be good to get an idea.

[MSTRS]

Carb settings may have an effect. BUT ignition timing is the big one. Higher octane needs more advance.
Since the spark must happen at a particular point BTDC, relative to the fuel being used, changing the fuel necessitates changing this spark point to suit. To get the maximum power and efficiency from an engine, the ignited gases must reach their full expansion, coupled with the maximum amount of compression being applied to those gases, which is just as the piston reaches the very top of it's stroke.
Low octane burns faster, so spark point must be closer to TDC.
In the case of an engine that has it's timing set for 98 (say), if you run 91 the fuel/air mix has finished burning before the piston reaches the top, which is why you get the knock or pinking - the expanding gases are trying to force the piston back down before the rotation of the crank will allow it. It has little or nothing to do with what's been called the 'diesel effect'. Incidently, diesels do have plugs...they glow to provide the heat source for ignition, which can only happen at or above a certain pressure.

[overworkedmonkey]

Carb settings may have an effect. BUT ignition timing is the big one. Higher octane needs more advance.
Since the spark must happen at a particular point BTDC, relative to the fuel being used, changing the fuel necessitates changing this spark point to suit. To get the maximum power and efficiency from an engine, the ignited gases must reach their full expansion, coupled with the maximum amount of compression being applied to those gases, which is just as the piston reaches the very top of it's stroke.
Low octane burns faster, so spark point must be closer to TDC.
In the case of an engine that has it's timing set for 98 (say), if you run 91 the fuel/air mix has finished burning before the piston reaches the top, which is why you get the knock or pinking - the expanding gases are trying to force the piston back down before the rotation of the crank will allow it. It has little or nothing to do with what's been called the 'diesel effect'. Incidently, diesels do have plugs...they glow to provide the heat source for ignition, which can only happen at or above a certain pressure.

So the type of fuel does matter based on your tuning. The next question is how do I find out what it has been tuned for?

[Ocean1]

So the type of fuel does matter based on your tuning. The next question is how do I find out what it has been tuned for?

Bung some 91 in, hook third gear at about 2k and wack the throttle wide open.

Listen carefully.

Seriously.

[overworkedmonkey]

Bung some 91 in, hook third gear at about 2k and wack the throttle wide open.

Listen carefully.

Seriously.

You mean to mix it in with what I already have in it or after?

[MSTRS]

:facepalm: Will this never end?
Run it on 91. If it pinks under heavy load (see Ocean's post) then go up an octane.

[TimeOut]

All this fecking stress and angst over octane.
V-tec already told you...he ran 91 in his CBR250RR race bike, and had excellent results. What more do you need to know?

As for ethanol - I believe Gull is the only servo with it present in their petrol. Some vehicles are not recommended to use their Force 10 (10% ethanol) but only because of possible damage to rubber seals in the fuel system. If you can't be sure - just don't use Gull.

Mobil has E10 at a lot of Wellington stations.

[SMOKEU]

I've used 91, 95, and 98 in my CBR250RR, with no noticable difference at all. I talked to some guys in Australia (Honda JDM CBR forums) (http://cbr250.com/forum/forum-4.html)

I wouldn't listen to anything those muppets on that CBR250 forum.

I also don't notice any difference on my MC19 if I run it on 91, 95, 98 or a mix of homebrew jungle juice.

[Phreak]

Lol those 'muppets' tend to behave a lot like the muppets on KB most of the time!

As in, some advice is good, others needs to be taken with a pinch of salt (or a kilo!) - just like some of the advice on this forum!

Besides, I have learnt a lot from asking the right questions of the right people, some of whom don't reside here in Kiwi-land.

(Maybe you don't like them cause they flame you for your posts...? Just a theory... Or maybe it's cause they BANNED you!)

[SMOKEU]

Lol those 'muppets' tend to behave a lot like the muppets on KB most of the time!

As in, some advice is good, others needs to be taken with a pinch of salt (or a kilo!) - just like some of the advice on this forum!

Besides, I have learnt a lot from asking the right questions of the right people, some of whom don't reside here in Kiwi-land.

(Maybe you don't like them cause they flame you for your posts...? Just a theory... Or maybe it's cause they BANNED you!)

Many of those people on the CBR250 forums seemed to have some sort of urine fetish. Don't ask me why. Yes, they banned me for "racist comments". I have to access the site through a proxy server now because my IP address has been banned from that site.

[Banditbandit]

There's a first time for everything.

:facepalm:

[SMOKEU]

:facepalm:

Are you alright there sir?

[Max Preload]

As long as the engine does not emit any "pinking" noise then from all the posts I have read on different forums the lower octane is better.You won't hear the most deadly (to engines) detonation noise... at higher rpm.

[Max Preload]

So whats the RON rating of a fuel got to do with how fast it burns?Lower RON fuel burns faster. That is to say, the rate of propogation of the flame front is higher. The peak cylinder pressure is reached sooner.

[MSTRS]

Which is what I was saying in post 52

[rok-the-boat]

Re: BMW R1150GS
From the Wiki, speaking of upgrades from the previous 1100GS: An anti-knock sensor adjustment change allowed the adventure version to run on lower quality gasoline as well.

From here: https://en.wikipedia.org/wiki/BMW_R1150GS

So, sounds like the electronics can detect and adjust via the ignition/fuel injection.

[Owl]

Wow nice dredge.

Anyway while I'm here, what's wrong with 95?

[TripleGee]

I Have a 1993 Kawasaki ZZR 400, what fuel should I be using? according to the specs it has a 12.8:1 compression ratio. and I'm using BP 98
but not all BP stations have 98 at there pumps
It's also in bad need of a tune but no bike shop around seems to be able to get it right and is running way to rich... I did a run up north to
Whangarei from west Auckland, 182kms to my destination and at 171kms I had to switch over to reserve. I use to get 230kms!!
So before I take it to someone else to try and tune, I want to put in the right fuel to start with.. Would 91 be sufficient? or 95?
Cheers

[layton]

I Have a 1993 Kawasaki ZZR 400, what fuel should I be using? according to the specs it has a 12.8:1 compression ratio. and I'm using BP 98
but not all BP stations have 98 at there pumps
It's also in bad need of a tune but no bike shop around seems to be able to get it right and is running way to rich... I did a run up north to
Whangarei from west Auckland, 182kms to my destination and at 171kms I had to switch over to reserve. I use to get 230kms!!
So before I take it to someone else to try and tune, I want to put in the right fuel to start with.. Would 91 be sufficient? or 95?
Cheers

I get 200km from a tank of gas with a rsv aprlia mille

[AllanB]

With the compression I'm thinking 95. 98 is fine too if BP is local. Bet you don't notice any difference between the two.

Mind you I bet the compression is south of the original figure by now.

[Yokomama]

I’m a huge nerd when it comes to economy and fuel types. I have a huge spreadsheet for the car but I’ve not got round to starting one for the bike.
My manual says I can use 91 or above (honda spada), as well as ethano fuel up to 10%, but NOT methanol (because everyone with a 250 has an abundance of that).

Anyway so far:

Mobil 95: 8.63L, 211km.
= 4.1L/100km
= 24.45km/L

Gull 91:
207km, 9.69L.
= 4.68L/100km
= 21.36km/L

Mobil 95: 199km, 8.71L
= 4.38L/100km
= 22.85km/L

The result I have for 98 is no good cuz it pretty much spat the dummy so I won’t post them.

[Scubbo]

fark the cbr is a boat compared to those, im getting ~ 11 KM/L ._. and trying to be sensible most of the time :wari:

[FJRider]

fark the cbr is a boat compared to those, im getting ~ 11 KM/L ._. and trying to be sensible most of the time :wari:

My FJ averages 14 km/L on most trips.

[TripleGee]

AllenB. No I don't notice any difference at all between 95 and 98 so I am thinking of going back to 95. But if I can, I wouldn't mind using 91 if my bike could handle it ok...

[TripleGee]

Yokohama.... These are the figures i use to get...

Gull 98 Bio Fuel :- 230km to 16 litres

BP 98 :- was similar at 229km to 16 litres

Caltex 95, Z 95 were the same at 220km to 16 litres

G.A.S. 95 :- 180km to 16 Litres and bike ran like a piece of S###

Discovered that I shouldn't have been using Gull Bio 98 due to the ethanol. And have been told this may have screwed up the jets in the carbs..
So I may have to get new kits for all four Carbs..

[Yokomama]

Ethanol attracts water
Water doesn’t like lots of metals
Lots of metals rust when they come in contact with water
= why gull 98 isn’t ideal in lots of cars and bikes.

[Jeeper]

Ethanol can play havoc on some types of rubber seals as well. Hence best to avoid unless bike manufacturer says it's safe to use.

[speedpro]

I'm not sure why but my scooter runs better on Gull 98.

As for flame speed, whatever the speed is in a still mixture it is too slow for anything but the slowest of really old engines. The squish causes high velocity gas to be ejected into the combustion chamber which causes turbulence and the fuel to be burnt in a short enough time to be useful. There are other methods of promoting the necessary turbulence. The useful feature of higher octane fuel is that it resists detonation of the yet to be burnt portions of fuel/air. This allows the use of higher combustion chamber pressures, either compression or boost, which then allows greater expansion of the burnt and heated gas and therefore more work extracted. Work extracted = torque. Detonation is violent and strips away the boundary layer of gas protecting the combustion chamber and piston from the searing temperature of the burning gas. If it happens often enough the alloy temperature is quickly raised to the point where it is weak and can be damaged by further detonation.

[pritch]

Some Mobil stations were using ethanol too. To answer your original question 95 should be OK.