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coil on plug motorbike

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  • coil on plug motorbike

    Hi, I am trying to sort cop on my bmw s14 engine and have read much info in using motorbike cop s..without going into too much detail are there any cops that do not require a cdi unit to run them? I will happily shorten or lengthen them to suit...
    Many thanks karl

  • #2
    The most common motorcycle coil used is probably the Denso (pencil looking) coil. Within a CDI environment it works great as it is a relatively low inductance coil. In a CDI ignition system a coil acts as a pulse transformer rather than an energy storage medium as it does in an Inductive Discharge System. That's why most IDI type coils, whether OEM or performance appear to be a little bulky, this is to make provisions for the coils. Mind you, the traditional bulky appearance of a IDI based coils have been stream-lined to work a lot more efficient. And on a side note, I have found that plasma technology integrated into IDI coils has worked rather splendid.

    However, to answer your question, I am not sure motorcycle coils will work well when used as a IDI solution on a naturally aspirated engine. By that I mean as the most ideal solution, not that it won't work. This is because the coil windings are too small to offer big energy through the inductive process. Albeit, my response is based on the basic understanding of the technologies mentioned and not on any specifics of the energy needs of the ignition system as required by the operational conditions of the engine.

    I hope this response has been helpful, cheers!
    Damien King
    Technical Analyst/Engine Management Calibrator
    Stephen's Automotive Research & Development Engineering


    • #3
      What is the ECU? An SMC?


      • #4
        Hi there,

        Thanks for your replies much appreciated. I have goat a SM4 v1.09 ECU.
        My understanding was that some of the motorbike coils are not CDI?
        If so I thought we could control the dwell time through the ECU.
        I thought somebody might have done this before and could identify some particular coils that could be controlled directly for the ECU without the need for CDI...

        Many Thanks


        • #5
          Is it that the max supply voltage from the ECU is too small to give a good spark?


          • #6
            As you have an SM4 you can use an ignition module with 2 pin motorcycle coils instead of a CDI. You will need a 4 channel module.

            The spark is generated from the ignition module switching the coil primary current off. Normally, motorcycle coils have small magnetic cores, which as SARDE mentions, limit the available spark energy. However, for a naturally aspired engine the coils and ignition module should be reasonable.


            • #7
              Hi. I use Honda CBR R 600 coils(Denso 129700-4510)- you will find them on ebay, I use a 0 227 100 211 Bosch ignition module they work really great with SM4, I have a 2,5L 16V naturally aspired engine. Dwell time look at this link:


              • #8
                Thanks a lot for your advise


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