Page 3 of 6 FirstFirst 12345 ... LastLast
Results 31 to 45 of 79

Thread: 91 or 98 fuel?

  1. #31
    Join Date
    30th July 2008 - 18:56
    Bike
    Road King
    Location
    In the sun.
    Posts
    2,143
    Blog Entries
    1
    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.
    Just another leather clad Tinkerbell.
    The Wanker on the Fucking Harley is going for a ride!

  2. #32
    Join Date
    13th December 2008 - 18:22
    Bike
    Your mom
    Location
    Christchurch
    Posts
    3,901
    Quote Originally Posted by overworkedmonkey View Post
    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.

  3. #33
    Join Date
    13th December 2008 - 18:22
    Bike
    Your mom
    Location
    Christchurch
    Posts
    3,901
    Quote Originally Posted by Flip View Post
    I agree with Smokeu on this one, and thats a first.
    There's a first time for everything.

  4. #34
    Join Date
    10th December 2010 - 09:49
    Bike
    None as yet
    Location
    Auckland
    Posts
    129
    Quote Originally Posted by Flip View Post
    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.


    Quote Originally Posted by SMOKEU
    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?

  5. #35
    Join Date
    13th December 2008 - 18:22
    Bike
    Your mom
    Location
    Christchurch
    Posts
    3,901
    Quote Originally Posted by overworkedmonkey View Post


    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.

  6. #36
    Join Date
    10th December 2010 - 09:49
    Bike
    None as yet
    Location
    Auckland
    Posts
    129
    Quote Originally Posted by SMOKEU View Post
    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.

  7. #37
    Join Date
    19th August 2007 - 18:49
    Bike
    GSX-R600 k8
    Location
    Palmerston Otago
    Posts
    2,176
    Quote Originally Posted by overworkedmonkey View Post
    #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 )

  8. #38
    Join Date
    13th December 2008 - 18:22
    Bike
    Your mom
    Location
    Christchurch
    Posts
    3,901
    Quote Originally Posted by overworkedmonkey View Post
    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.

  9. #39
    Join Date
    19th August 2007 - 18:49
    Bike
    GSX-R600 k8
    Location
    Palmerston Otago
    Posts
    2,176
    Quote Originally Posted by Flip View Post
    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.

  10. #40
    Join Date
    9th November 2006 - 18:42
    Bike
    Ducati V4S Streetfighter
    Location
    Orewa, Auckland
    Posts
    4,120
    Blog Entries
    1
    Quote Originally Posted by SMOKEU View Post
    My bike feels the same on 91 and on 98 octane fuel.
    Try aircraft AVGAS. WOOHOO!

    Or a Y2K bike

  11. #41
    Join Date
    10th December 2010 - 09:49
    Bike
    None as yet
    Location
    Auckland
    Posts
    129
    Quote Originally Posted by SMOKEU View Post
    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.

  12. #42
    Join Date
    8th November 2004 - 11:00
    Bike
    GSXR 750 the wanton hussy
    Location
    Not in Napier now
    Posts
    12,765
    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.
    Do you realise how many holes there could be if people would just take the time to take the dirt out of them?

  13. #43
    Join Date
    10th December 2010 - 09:49
    Bike
    None as yet
    Location
    Auckland
    Posts
    129
    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.
    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.

  14. #44
    Join Date
    13th December 2008 - 18:22
    Bike
    Your mom
    Location
    Christchurch
    Posts
    3,901
    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.

  15. #45
    Join Date
    10th December 2010 - 09:49
    Bike
    None as yet
    Location
    Auckland
    Posts
    129
    Quote Originally Posted by SMOKEU View Post
    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.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •