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  • Pinging

    I'd like to know what you are all using for fuel. My '93 Seven with the 1700 Crossflow requires 93 octane, which as we know is not available in Ca. The 91 octane that is available causes pinging. I've been using octane enhancers which seem to work, but am concerned with the possible side effects (oil contamination, degrading rubber hoses, etc) . Should I be concerned? Any other suggestions, short of retarding the timing? Thanks!

  • #2
    Dave Walker's excellent book "Engine Management" cites advanced ignition timing as the sole reason for pinging (or pinking as he calls it).

    He also states that the sound stems from the pressure rising too early, resulting in pisting rattling as it goes over TDC.

    Pinking is the precursor to knocking, where a second flame front is created during combustion due to auto ignition. Knocking is dependent on, among other things, the octane level.

    Pre-ignition/Detonation is the phase following knocking, where the mixture auto ignites on its own without the aide of a spark plug.

    I could give some spectulative/experimental advice on spark plugs, but since this may be an engine killer, I will keep my mouth firmly shut.

    Retard your ignition...

    /Magnus F.


    • #3
      After consulting with an engine expert on the subject, I can post a few additional hints.

      My plug theory wasn't totally off: Try to switch to colder plugs, which will lower the overall temperature in the combustion chamber, thus preventing auto ignition. This may give you an engine that is harder to start, though. Also colder spark plugs may lead to the carbon deposits described below.

      If your engine burns oil or have been running rich, your combustion chambers may have deposits in them, whose glowing facilitates auto ignition. A very radical cleanout solution to this problem is given in the link below. Apply at your own risk. It worked fine for my old Volvo, but I will not vouch for the method at all.

      /Magnus F.


      • #4
        There's a Unocal in Pasadena (corner of Glenarm & Arroyo Pkway) that sells the 100 octane 'racing gasoline'. Supposedly there's one in Agoura at the exit of Palo Camado Rd. (before Kanan when heading North) that does so as well but I haven't personally purchased any there.

        Here's just one of the many nice descriptions I've found describing the whys and whats of octane:

        Interesting that a fluid w/ lower BTUs creates more heat energy than one w/ higher BTUs.

        It's expensive, so I mix it to get it w/ the 91 to produce my own PON (PON+PON/2). It's not really a problem in my engine so far as the compression ratio isn't that high. Yet.
        A day you don't go a hundred is a day wasted


        • #5
          Thanks for the replys! I'll try to fnd that gas station in Agoura.