Fitting Bosch Red Coils - I am confused by the wiring ... | FerrariChat

Fitting Bosch Red Coils - I am confused by the wiring ...

Discussion in '308/328' started by 348KYD, Nov 7, 2019.

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  1. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #1 348KYD, Nov 7, 2019
    Hi All,

    I have done a lot of searching but can't find the definitive answer to my confusion. (the car is an early 1978 carb car with twin dizzys and points)

    I have bought new Bosch Red coils and new external resistors in order to rule these out of my poor running diagnosis.

    My experience with ballast resisted coils is that the resistors are wired between the ignition feed and the coil, but the current stock resistors are between the negative coil terminal and the points.

    Does anyone know how I should wire in the new resistors and coils?

    Thanks, Nick.
     
  2. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #2 348KYD, Nov 8, 2019
    The more I think about it, the less sense it makes to me ...

    A ballast resisted coil has the resistor between 12v feed and coil so the coil normally operates with a reduced voltage. There is then an additional feed from the starter solenoid that gives it an unresisted feed during starting. My 308 has neither of these so I assume it is a "normal" 12v coil as standard, in which case the Bosch Reds are incorrect.

    The original resistor between the coil and the points therefore reduces voltage to the points, rather than to the coil as above - I can't see the point in this, I'm now not even sure if the module under the standard coils is a resistor ....

    Any thoughts?
     
  3. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #3 348KYD, Nov 12, 2019
    I'm chatting to myself in this thread but I'll carry on :)

    I can't reconcile the theory so I'm going the popular route of Pertronix 9MR-183 with Flamethrower II coils and ACC 4040R leads from Summit Racing, then I can remove the existing stuff that I don't understand!!
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,123
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #4 Steve Magnusson, Nov 12, 2019
    Last edited: Nov 12, 2019
    Is this a US version 1978 308GTS (even though you are in the UK)? Can't comment about the appropriateness of the Bosch Red Coils, but the additional unresisted +12V feed to the coils during starting went away on '78 US, and the ballast resistor is located between the coil and the points (as it doesn't matter which side of the coil it is on without the unresisted +12V feed for starting).
     
  5. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #5 348KYD, Nov 12, 2019
    Hi Steve, yes, it's a US car, I imported it earlier this year.

    I still can't see the point (pun not intended) of the reduced voltage to the points ...

    Cheers, Nick.
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,123
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #6 Steve Magnusson, Nov 12, 2019
    If you do an internet search on "why do I need a ballast resistor" that will get you some discussion. To do the "unresisted" starting thing, you have to have one, but, without that, it's more the coil design requiring it (to limit the current) - so you could maybe design the coil to not need one, but doing a custom coil for a small volume car doesn't make sense.

    If I may make some suggestions:

    1. In your Profile, where you have "1978 308 GTS", please change this to "1978 308 GTS (US version)" -- since your version doesn't match your location ;),

    2. If you don't have one, get a copy of the 150/78 OM for the US version. You might try contacting Maranello Concessionaires as they had a lot of the older F literature at very reasonable prices in the past. If you can't find one, give a shout, and I can put a pdf copy up on my Dropbox and post the link (but an official printed one is much better quality, and an asset for any F IMO).
     
  7. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #7 348KYD, Nov 12, 2019
    Thanks Steve, All good advice. I'll try and get the OM ....
     
  8. 348KYD

    348KYD Karting

    Jul 29, 2007
    65
    Bedfordshire, UK
    Full Name:
    Nick
    #8 348KYD, Jan 20, 2020
    For completeness, in case anyone finds this in the future ...

    I removed the original coils and resistors, and the copper core HT leads.

    I fitted the Pertronix, Flamethrower coils and suppressed leads (didn't use the 8mm ones as they didn't fit into the dizzy caps, so bought some 7mm suppressed leads instead).

    The difference is significant, timing on both banks spot on and no fluctuation at all - everything controlled from one dizzy now, feels much better.
     

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