Coil on Plugs ignition on a 308 with points? | FerrariChat
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Coil on Plugs ignition on a 308 with points?

Discussion in 'Technical Q&A' started by Birdman, Nov 2, 2004.

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  1. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    THE Birdman
    #1 Birdman, Nov 2, 2004
    OK, a brainstorm for all you techno gurus to consider...

    We all know the basic advantages of a coil-on-plug ignition. (High voltage delivered right to the plug without needing long wires and possibly distributors to get to there from the coils).

    So lets say I wanted to put a set on a 308, retaining the points and distributors. In such a system, I would use the distributors to "distribute" the low voltage firing signal from the points, rather than the high voltage from the coils.

    Advantages are lower wear on the points and distributor contacts, higher voltage on the plugs, therefore better performance along with much longer distributor and point life. It requires very little modification from stock also, which is attractive to many people.

    This seems too good to be true. Somebody tell me why it can't be done.

    Birdman
     
  2. DGS

    DGS Seven Time F1 World Champ
    Rossa Subscribed

    May 27, 2003
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    DGS
    #2 DGS, Nov 3, 2004
    I've heard on this forum that somebody is doing such a conversion (plug mounted coils). I haven't heard the results.

    The deep plug wells on the 3x8s seems tailor made to plug mounted coils ... BUT - if you've ever tried to hold a plug extender pulled out of a hot engine, you know that those wells get a smidge warm. The plug mounted coils developed for motorcycles sit out in the airflow. I don't know the long term effects of cooking the coils. (Chevy is starting to put plug mounted coils on their cars ... but how long does a Chevy last, anyway? ;) )

    However, you can't just trigger this kind of coil by "distributing" the points. A traditional breaker point ignition system closes the point contact while charging the coil (electromagnetically), then opens the points to fire the coil. (Technically, the coil's electromagnetic field "collapses" into a current spike on the HT side of the coil. The "condensor" simply prevents arcing on the points as they open.) The open/close period of the points is the dwell. For plug mounted coils, you'd probably have to put some electronics in to trigger it.

    But one of the advantages of individual coils is that you can eliminate the distributors (and the expensive caps and rotors). Also, a breaker point ignition doesn't really produce the kind of voltage you need for modern platinum plugs, so you're better off with an electronic (capacitive discharge) ignition system.
     
  3. boxer frank

    boxer frank Karting

    Sep 30, 2004
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    toronto canada
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    FRANK
    #3 boxer frank, Nov 3, 2004
    low voltage u want to run to save your rotor and cap won't jump the gap between your rotor and cap to fire your cop's
     
  4. jeffdavison

    jeffdavison F1 Rookie

    Jul 29, 2002
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    Jeffrey Davison
    #4 jeffdavison, Nov 3, 2004
    They sit deep in the head, not in the flow. See pic:


    JD



     
  5. Verell

    Verell F1 Veteran
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    May 5, 2001
    7,022
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    Verell Boaen
    #5 Verell, Nov 3, 2004
    A Dodge Stealth/Mitsu 3000 uses deep well coil plugs that just might fit.
    Remember thinking this when doing the major on my son's car.

    Distributor show-stopper: the distributor rotor never actually contacts the tips in the cap, just comes within a few thou so the spark can jump.

    However, there are several reliable engine control systems that can drive the coil packs (Haltech, TEC, etc.) and are already setup for V8s with software for tuning ignition advance vs RPM, manifold vacuum, etc. Then you're all electronic.
     

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