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Thread: 91 or 98 fuel?

  1. #1
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    10th December 2010 - 09:49
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    91 or 98 fuel?

    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?

  2. #2
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    It'll make you "feel" faster.


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  3. #3
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    19th April 2007 - 10:04
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    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.

  4. #4
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    13th July 2008 - 20:48
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    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.

  5. #5
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    3rd November 2007 - 07:46
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    Where's the 95 option?

    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.
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  6. #6
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    31st July 2008 - 12:29
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    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.

  7. #7
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    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.

  8. #8
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    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.
    Do you realise how many holes there could be if people would just take the time to take the dirt out of them?

  9. #9
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    Quote Originally Posted by overworkedmonkey View Post
    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.

  10. #10
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    12th November 2010 - 10:00
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    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

  11. #11
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    Quote Originally Posted by superman View Post

    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.

  12. #12
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    Quote Originally Posted by SMOKEU View Post
    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.

  13. #13
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    19th April 2009 - 18:52
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    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

  14. #14
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    31st July 2008 - 12:29
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    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.

  15. #15
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    Quote Originally Posted by overworkedmonkey View Post
    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.

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