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Octane Question

Discussion in 'Technical and Troubleshooting Torque' started by Jastel, Jan 11, 2016.

  1. Hi guys, I have a 96 CBR900 which I have always run on Caltex 95 (Except for the time I was forced to use an Independent and had nothing but dramas) with no issues. Anyways yesterday I ran the tank empty on a run to see what range I now get and the closest servo to me gave me an option of E10 or 98..... there was no way I was using E10 so I filled with 98. After a few minutes I noticed it was popping and crackling out the exhaust on downshifts way more than usual and when I arrived at my destination I could smell a strong whiff of unburnt fuel. Same thing happened on my return home but when I opened up the throttle on the motorway it missed and farted til I backed off.
    Now I'm assuming the higher octane fuel is no good for my older engine?

    I checked the handbook (so happens they contain a wealth of useful info lol) and it says to use 91 or above.
    Now I've drained the tank and was wondering do I try 91 or just keep using Caltex 95?
    I haven't run 91 in anything for years and just assumed it all (sneakily) contains ethanol now so can anyone make a recommendation on 91 fuel?
  2. If it says 91 or above it means you can use 91. Unless you notice some significant improvement in using a higher octane I would be saving money by using the cheaper 91.

    I am a bit surprised though. I would have expected that CBR would like a higher octane, but the manufacturer should know what they are talking about.
  3. Yep, 91 is the way to go, no ethanol unless stated at the bowser.
  4. Octane is a (proportional) measure of the resistance to ignition. Higher octane is harder to ignite. This is consistent with what you experienced, although it usually doesn't make that much difference.

    Contrary to popular belief, higher octane fuel does not produce more power. What it allows is for a engine to be tuned produce higher power, without pre-ignition (pinging).

    The "cleans your engine as you drive" is pure guff, petrol is a solvent so all petrol will clean your engine.
    • Like Like x 1
  5. Yeah I would never have used it if the other option was better than E10.
  6. Wait for a hot day, find a big hill and using a high gear open the throttle and listen for the can of marbles. No marbles and the octane is fine, hear marbles and use a higher octane. I am surprised your hi performance bike, high compression did not like 98. But who knows what cleaver stuff Mr Honda has done.
  7. Ignition timing plays as big part, so even very high compression engines can run 91 if tuned for it.
  8. My bike is spec'd for 91. It runs fine on 95 but not so good on 98. If I had to put 98 in or enjoy sitting on the side of the road, I'd put in enough 98 to get me to a servo with the lower octane stuff.

    It is really pissing me off that 95 is getting harder and harder to find, replaced by the E10 scam. My bike runs fine on E10/94 btw, but it is not recommended by Yamaha so again, it is used only when I have no choice of 91 or 95.
  9. I actually struggled tonight to find 91... most had only E10 or 98 and a few also had the 95.
  10. Possible you have picked up a lot of crap out of the bottom of the tank by doing this, and created carb issues. Drain the carb bowls into a container and see if any debris comes out with the fuel.
    • Agree Agree x 3
  11. By that I mean I ran it down to reserve, there was no crap in the tank, filter or fuel valve assembly when I removed them this afternoon.
  12. I can't remember the exact year, but when I got the first of the 600 Hornets to make it to Oz, it was, by the owner's book, happy to run on 91, but I, being a curious type, tested it with 98 and 95, and found that, using 98 allowed me to travel much further on a tank of fuel than I could using 91.

    To be honest, I never could find a satisfactory explanation <shrug> but, when I was on a longish trip, I'd always use 98 for the greater range, and I avoided E10 like the plague.
  13. Unless your bike has a knock sensor, it's probably due to confirmation bias. or maybe quantum.
  14. It definitely happened.

    The bike had carbs, and I assume that there was some slight difference in the density of 98 as opposed to 91 and that slight difference made it more economical.

    Or, as you say, perhaps it was quantum.

    It was a blue bike with yellow wheels and seat..... maybe that had something to do with it. :)
    • Like Like x 1
  15. I always find I get a bit further on a tank of 98 than I do on a tank of 95. However the difference isn't worth the extra cost, so I use 95 where I can get it.
  16. I have my bike since early Dec 2015 and I've been putting in 98 Octane.. My manual says 91 or higher and I just figured the higher the octane the better? But thats just my assumption - not sure if its right or it really matters so long as its 91 or higher. Bike is a CBR250R. A tank usually lasts me week and a half and I commute into work everyday and back. Thats 52kms return everyday. So should I just use 95 or continue with 98?
  17. If a motorbike runs happily on lower octane fuel, and the manufacture, who probably knows the bike better than most. sez it's OK to use 91, then why not try it......
    try 95 too.

    As I said before, I'd avoid E10 like the plague, but many bikes will run perfectly happily on 91 (with no Ethanol).

    When I had my Triumph Street Triple, the book said 91 was OK.

    I tried 91, 95 and 98 and found no measurable difference, so it got fed 91 when I could find it, and 95 if I NEEDED fuel and the servo only had E10.
  18. #18 ibast, Jan 12, 2016
    Last edited: Jan 12, 2016
    I used to get better milage on 95 than 91 with the gsxr. My theory was that the ignition was borderline too far advanced. This was supported by the fact I would get pinging on some 91s and some hot days.

    I theorised that some bike sit on the limit in terms of compression ratio and timing and thus do benefit from a higher octane fuel.

    It all went out the window when they started makeing 95 by mixing ehtanol etc. then the differrence was more to do with brand and their blending policy.

    As to the OP it does read like you got a bad batch of 98. this is not uncommon with wet weather and/or change in season. You should consider reporting the petrol station. Department of land and environment used to be the place. not sure now.
  19. I would just say don't trust that the label on the pump is telling you the truth about what you're buying.
    Fuel retailing business is notoriously dodgy and always has been.
    • Agree Agree x 1
  20. Higher isn't better if you don't need it and may be worse. Some bikes designed for 91 run worse on 98.

    If the manual says 91 use it unless you have a good reason not to. 98 is probably just a waste of money.