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Thread: 91 or 98 fuel?

  1. #46
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    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.
    ... and that's what I think.

    Or summat.


    Or maybe not...

    Dunno really....


  2. #47
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    Quote Originally Posted by vifferman View Post
    The octane rating in simplistic terms is the measure of a flammable substance's propensity to 'knock'
    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.
    Go soothingly on the grease mud, as there lurks the skid demon

  3. #48
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    Quote Originally Posted by vifferman View Post
    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.

  4. #49
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    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.
    Do you realise how many holes there could be if people would just take the time to take the dirt out of them?

  5. #50
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    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) 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?
    1990 CBR250RR - fully rebuilt and awesome!
    1999 CBR900RR - a work in progress...

  6. #51
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    Quote Originally Posted by Phreak View Post
    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) 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.

  7. #52
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    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.
    Last edited by MSTRS; 15th December 2010 at 09:28.
    Do you realise how many holes there could be if people would just take the time to take the dirt out of them?

  8. #53
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    Quote Originally Posted by MSTRS View Post
    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?

  9. #54
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    Quote Originally Posted by overworkedmonkey View Post
    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.
    Go soothingly on the grease mud, as there lurks the skid demon

  10. #55
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    Quote Originally Posted by Ocean1 View Post
    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?

  11. #56
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    Will this never end?
    Run it on 91. If it pinks under heavy load (see Ocean's post) then go up an octane.
    Do you realise how many holes there could be if people would just take the time to take the dirt out of them?

  12. #57
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    Quote Originally Posted by MSTRS View Post
    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.

  13. #58
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    Quote Originally Posted by Phreak View Post
    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)
    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.

  14. #59
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    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!)
    Last edited by Phreak; 15th December 2010 at 23:08. Reason: New information brought to light...!
    1990 CBR250RR - fully rebuilt and awesome!
    1999 CBR900RR - a work in progress...

  15. #60
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    Quote Originally Posted by Phreak View Post
    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.

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