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What fuel!?!?...and other questions

Discussion in 'Bay Tech Clinic' started by Sarezomatic, May 22, 2007.

  1. cammokombi

    cammokombi New Member

    Messages:
    1,562
    Location:
    Melbourne Victoria
    Re Fuel additive for valves...

    I have been told that Spitfire is better than Nulon. What do the myth busters say?
     
  2. Blue76Bay

    Blue76Bay New Member

    Messages:
    26
    Location:
    Western Sydney NSW
    I remembered reading something in the Bently Manual about unleaded fuels. Check out the Fuel Injection Page 2.

    "Whether equipped wih carburetors or fuel injection, all VWs covered by this Manual are designed to operate on regular (91 octane) gasoline. Lead-free gasoline is reguired for fuel injection cars that have catalytic converters."
     
  3. syncro

    syncro Well-Known Member

    Messages:
    10,371
    Location:
    Southern Highlands
    Bentley is US fuel not third world fuel like Australia.
     
  4. cammokombi

    cammokombi New Member

    Messages:
    1,562
    Location:
    Melbourne Victoria
    Arrrrrrgh!

    [​IMG]
     
  5. Blue76Bay

    Blue76Bay New Member

    Messages:
    26
    Location:
    Western Sydney NSW
    Just out interest do you have any Web Links that discuss this? I am always keen to learn more.

    Are you saying 91 octane fuel US does not equal 91 octane fuel Australia?
     
  6. kombikid76

    kombikid76 New Member

    Messages:
    652
    Location:
    sunny sydney
    http://type2.com/bartnik/octane.htm

    "Octane has to do with the resistance of a fuel to preignition"

    "A fuel with a high octane number is more resistant to preignition than a fuel with a lower octane number. The only reason you would NEED high-octane fuel would be if you had a high-compression engine, which you don't if you have a stock VW air-cooled engine. "

    This makes sense, maybe some1 would like to look into burning temps of PULP vs ULP and post their finding... But at the moment my interpretation is exactly as stated on that site; higher RON = less likely to ping. So using PULP is a safe gaurd for an out of tune vw that might ping or run hot. In essence a reasonably well maintained stock vw should not ping under any circumstances (thats why they are still around).

    Ive run ULP in my buses for as long as ive owned them (all of 4 yrs) and ocassionaly put in some PULP but the only difference i have ever picked up is the higher resistance to pinging which could be interpreted as enabling you to squeeze a bit more power out of your bus (would need to adjust timing).

    This topic has been pretty heavily discussed on http://forums.aussieveedubbers.com go have a search, many many different opinions.
     
  7. kombikid76

    kombikid76 New Member

    Messages:
    652
    Location:
    sunny sydney
    Compression Octane Number Brake Thermal Efficiency
    Ratio Requirement ( Full Throttle )
    5:1 72 -
    6:1 81 25 %
    7:1 87 28 %
    8:1 92 30 %
    9:1 96 32 %
    10:1 100 33 %
    11:1 104 34 %
    12:1 108 35 %

    stock vw is 7.5:1 or 7:1 so im guessing between 6 and 8:1 would a reasonable assumption

    Another point i had not considered:

    7.8 What is the effect of engine deposits?

    A new engine may only require a fuel of 6-9 octane numbers lower than the
    same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to
    the formation of a mixture of organic and inorganic deposits resulting from
    both the fuel and the lubricant. They reach an equilibrium amount because
    of flaking, however dramatic changes in driving styles can also result in
    dramatic changes of the equilibrium position. When the engine starts to burn
    more oil, the octane requirement can increase again. ORIs up to 12 are not
    uncommon, depending on driving style [27,28,32,111]. The deposits produce
    the ORI by several mechanisms:-
    - they reduce the combustion chamber volume, effectively increasing the
    compression ratio.
    - they also reduce thermal conductivity, thus increasing the combustion
    chamber temperatures.
    - they catalyse undesirable pre-flame reactions that produce end gases with
    low autoignition temperatures.


    Plenty more variables that will affect the RON requirements of an engine on http://www.faqs.org/faqs/autos/gasoline-faq/part1/preamble.html

    time for bed tho, got maths lecture at 8am :-(
     
  8. Schmoburger

    Schmoburger Active Member

    Messages:
    4,382
    Location:
    Nowra/Jervis Bay area, NSW.
    Presumably an octane rating of 91 in Australia would be the same as 91 in the US tho would it not?

    Australian fuel may be dirtier depending upon the supplier or individual stations, and may go off within a shorter space of time, however I would think that the moment you put a 91 RON fuel in the tank, it would have the same combustion characteristics as any other fresh 91 RON fuel whether it be sold in ENgland, US, Australia or Nigeria... as octane ratings are a constant. :)
     
  9. paul

    paul Member

    Messages:
    217
    Location:
    Epping, Melbourne
    Click here for the difinitive answer on fuel and the VW AC engine:)
    The Short answer is there are two ways of measuring octane rating and of course Aus and the US both use diferent methods so no.... US 91 MON octane does not equal Aus 91 RON octane :rolleyes: Those crazy yanks.....go figure.
    Paul.
     
  10. LOSTY

    LOSTY New Member

    Messages:
    44
    Location:
    Melbourne
    Both specs of fuel are sold in Australia from time to time , our local spec is based on Europe's , we also ship in fuel from Singapore which is made to US spec , The early Fuel sold at the Safeway (Woolworths) servo's was nearly all US spec sourced mainly from overseas but now its a mix of both like all other servo's here are selling
     
  11. syncro

    syncro Well-Known Member

    Messages:
    10,371
    Location:
    Southern Highlands
    No it is not.
     
  12. syncro

    syncro Well-Known Member

    Messages:
    10,371
    Location:
    Southern Highlands
    Read point 2 of my post, not point 3.
    Air cooled engines have a different set of problems.
    If it is pinging, it is very very bad.
    I wouldn't even use 91 RON third world garbage in my lawnmower.
     
    Last edited: May 24, 2007
  13. cammokombi

    cammokombi New Member

    Messages:
    1,562
    Location:
    Melbourne Victoria
    Petrol question

    I always carry 80 ltres of petrol in jerry cans. Does petrol go off? How long will it store?
     
  14. Van Housing

    Van Housing Well-Known Member

    Messages:
    10,434
    Location:
    Yarraville Vic
    I think petrol goes off the same way fireworks go off.. with a stray spark... :D

    Petrol is a mix of relatively stable hydrocarbons - unless the fuel is contaminated, or there is an input of energy to break chemical bonds (eg a flame), it shouldn't have anything with which it can react so shouldn't "go off". (ie it should last "for ages")
     
  15. paul

    paul Member

    Messages:
    217
    Location:
    Epping, Melbourne
    Unleaded fuel will go off fairly quickly if exposed to air (ie in your vented fuel tank) to the point of turning in to brown tar like crud if left for a very long time(we are talking lots of years here), but it should keep well in sealed jerry cans as there is nowhere for the volatiles to go.
    Paul
     
  16. kombikid76

    kombikid76 New Member

    Messages:
    652
    Location:
    sunny sydney
    "excessive heat caused by low octane fuel"

    Yea, i didnt quite understand that... From what ive read (all 30 mins on the web of it) havent come across anything saying lower octane fuels burn hotter only that octane rating is essentially the fuels resistance to pre-ignition for wat eva reason.

    I can see that pinging would cause excess heat but other than that im lost...

    *searches for enlightenment*

    ;-)
     
  17. syncro

    syncro Well-Known Member

    Messages:
    10,371
    Location:
    Southern Highlands
    It is really only a problem with air cooled engines. They can't get the heat away from the valve as quick as a watercooled head. Then you also get pinging from the hot spots.
     
  18. kombikid76

    kombikid76 New Member

    Messages:
    652
    Location:
    sunny sydney
    yea i get that; but i cant see how the octane rating of the fuel effects the build up of heat... nowhere have i seen anything suggesting that lower octane fuels burn hotter... only that they are more likely to ping which will send combustion soaring.

    hence the fuel grade you need to run is totally dependant on the combustion characteristics of your engine such as A/F mixture, timing advance, combustion chamber hot spots and most importantly compression ratio. So i would see this as meaning use the lowest possible octane value fuel that your engine can run without pinging under any circumstances. So if your using ULP and your engine isnt pinging then you dont need to run PULP....?
     
    Last edited: May 24, 2007
  19. syncro

    syncro Well-Known Member

    Messages:
    10,371
    Location:
    Southern Highlands
    Yes, that's the pinging problem but not the burning valves.

    A few of the people I work with have had knock sensor failures causing their engines to ping. This would mean that they should be using higher octane fuel. Two were Falcons one was a Subaru which were supposed to be designed for 91.

    It can never hurt to go for a higher octane, but it can be expensive to go lower.
     
  20. kombikid76

    kombikid76 New Member

    Messages:
    652
    Location:
    sunny sydney
    without the knock sensor yea, but knock sensors are designed to run the engine at its optimum for the available fuel grade being used....


    So why does lower octane fuel cause the valves to burn?
    (interested not having a dig)
     

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