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Does the resistence of the effect electronic

Discussion in 'Technical Q&A' started by stephenofkanza, Feb 4, 2010.

  1. stephenofkanza

    stephenofkanza Formula Junior

    Mar 5, 2005
    542
    Kansas
    Full Name:
    Stephen LeRoy Sherma
    #1 stephenofkanza, Feb 4, 2010
    Last edited: Feb 4, 2010
    Do you know if the 'resistence' or lack there of has the same effect that using the correct or wrong spark plug wires on our electronic ignition.

    Hope that was clear.

    Stephen

    Mine is an 81 308 GTSi
     
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  3. Skidkid

    Skidkid F1 Veteran
    Rossa Subscribed Owner

    Aug 25, 2005
    6,654
    Campbell, CA
    Full Name:
    John Zornes
    Sorry, clear as mud

    Low resistance wires produce a hotter spark but the high frequency components of the spark throw off a LOT of RF noise. Resistor wires remove the very high frequencies (RC filter) so the rising edge is slower. This makes a slightly cooler spark and reduce the RF noise.
     
  4. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    27,114
    Austin TX
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    Brian Crall
    RF can be a real problem in the Marelli Digiplex and Microplex ignition systems. We (Collectively....the dealers, shops etc.) have had trouble with that since 1980. It is why I use nothing but Cavis or Taylor spiral wound. I have seen way too many troubles caused by other wire.
     
  5. boatr2001

    boatr2001 Karting

    Oct 3, 2006
    88
    Rockford,IL
    Follow-up question for the experts, Is the RF interference merely an annoyance, or can improper (ie. lack of) resistance actually damage the digiplex boxes?
     
  6. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    27,114
    Austin TX
    Full Name:
    Brian Crall
    No damage done it can just make the car run like crap. It can also be very intermittant.

    The cables to the ignition boxes run close enough to the secondary side of the ignition they act like antennas. We know from experience that on the 308/328/Mondial it is the cable to the diagnostic plug that picks up the interference. It was really profound when the Jofatron that the plug was designed for was plugged in.

    The TRs had serious problems sometimes just from a different brand of plug. There was a shortage in the late 80's of the correct Champion so the factory told us to source Bosch plugs locally. Sometimes after a service with those the cars just ran terrible with the different plugs from RF. We found the NGKs didn't cause it so against policy we used them. In the 355/550 days Ferrari finally switched to NGK and we never had a plug problem again.
     
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  8. boatr2001

    boatr2001 Karting

    Oct 3, 2006
    88
    Rockford,IL
    Great follow-up answer...thank-you
     
  9. smg2

    smg2 F1 World Champ
    Sponsor

    Apr 1, 2004
    12,015
    Dumpster Fire #31
    Full Name:
    SMG
    RF is the function of the EM wave. there is a resonance set up, defined with Maxwells eq. the coils discharge at high AC voltage with low amps and the skin effect is now how the EM wave travels, the resonance frequency is in the UHF range, if you wanted to get real techy you can calculate the needed wire length to match the frequency based upon it's core construction and coil windings to insure the EM wave arrives at the plug at the right time. as the time of the wave to propagate the wire is a function of the frequency, permittivity of the medium and resistance it will slow from the speed of light. doesn't sound like at those speeds it would be a big deal but given the ms/sec^2 of the TDC events it does add up. this of course is fine tuning to the Nth degree because you could then treat it like a lone transmission and calculate the node/anti-node to reduce resonance and increase efficiency.

    And don't run the coil with a lead pulled from the plug and no ground discharge, the inductance voltage on the secondary windings can't take that voltage for sustained periods. There's lots of physics in ignition systems.

    cross inductance is another issue and why the move to COP is preferred. now the resonance between all the coils need to be matched within an acceptable percentage.

    so there's the EE part of the reason. CB Radio guys should have a really good handle on this.
     

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