Spark plug show and tell - extended duration of wide open throttle

Discussion in 'General Questions' started by Fabian, May 11, 2014.

  1. Fabian

    Fabian Well-Known Member

    I've brought this thread to fruition to see what people are doing with their fuel mixture settings as described by the firing end of the spark plug after prolonged periods of wide open throttle; with the engine working at your chosen rpm band, and chosen oil/fuel ratio and chosen fuel octane number (in your specific location) and chosen cylinder head and chosen CDI & ignition curve settings and chosen jet size, and the approximate height above sea level where the long distance wide open throttle run took place and the air temperature and air humidity at the time, and the cylinder head temperature and exhaust gas temperature if you have that information.

    My photos represents prolonged periods of wide open throttle between 3,500 and 3,800 rpm, using Australian (lower eastern states) 98 octane fuel and 25:1 oil/fuel ratio and a CR Machine Manufacturing low compression straight plug billet cylinder head and a Jaguar CDI using jumper settings selected for the most advanced ignition curve.
    I am running a No 77 jet in the NT carburettor with atmospheric conditions at the time being an 18 degree (65 degrees Fahrenheit) day with 59% humidity and approx 120 meters elevation above sea level.
    The cylinder head temperature was 140 degrees Celsius (266 degrees Fahrenheit) and the exhaust gas temperature (read from an onboard KOSO EGT sensor and gauge) was 370 degrees Celsius (700 degrees Fahrenheit).

    The flash pic shows more detail of the firing end.


    Last edited: May 11, 2014

  2. sactownie

    sactownie Member

    98 octane????? Oh I forgot you are in Australia 98 octane there is the same as the 93 here in the US Nice looking plug though, the exact color you want it
  3. Fabian

    Fabian Well-Known Member

    It's as close as what could be described as the perfect plug colour, which is representative of the carburation being tuned to perfection.