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what's with Marelli BK3A coils?

Discussion in 'Technical Q&A' started by Ferraripilot, Jul 25, 2009.

  1. Ferraripilot

    Ferraripilot F1 World Champ
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    May 10, 2006
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    I was reading an Alfa Romeo book the other day and the author mentioned the Marelli BK3A coil as the greatest canister style coil ever. Their resistance is a very low at .8 ohms. Ohms are definitely not the end all factor when it comes to coils. My Bosch Red coil (super coil) has 2.1 ohms resistance and there is a positive difference in how my engine runs with this coil compared to that of say the stock Marelli coils which register at 1.1 ohms resistance.

    I called GT car parts and they agreed that the BK3A coils are fabulous, so fabulous that they are very difficult to get and when they do have them they go for about $400 a pop! What is the deal people?
     
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  3. sammyb

    sammyb Formula 3

    Jun 23, 2006
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    Ummm...I call B.S.. I'm sure they're fine, but I'd guess they're really no better or worse than any modern coil with similar specs.
     
  4. Ferraripilot

    Ferraripilot F1 World Champ
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    ebay item 370239265858

    what the heck is so special about these coils that they bring $479, or even have the guts to ask that much! for an ignition coil! someone tell me. wow
     
  5. staatsof

    staatsof Seven Time F1 World Champ
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    I don't know either but I just replaced the Mareli coils on my 71 Espada with a pair of new Pertronix for $70 and it made very noticeable difference.
    Of course they were pretty old. Maybe this price is just for an original looking coil for show? I can just paint mine, slap a Marelli label on them, use the old brackets and resistors and it will be darn hard to tell the difference.

    Bob S.
     
  6. alhbln

    alhbln Formula 3
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    #5 alhbln, Aug 8, 2010
    Last edited by a moderator: Sep 7, 2017
    (Reactivating an old thread) The prices you see with dealers and on ebay seem to be based on the fact that the coil was used in Ferraris and Lamborghinins and is not available anymore except as NOS.

    I hate to destroy a myth :) but the BK 3A is nothing special or exotic regarding the electrical parameters or spark output.
    The BK 3A was Marelli's product name, the actual coil is a BZR201R which is the successor of the more easily to source BZR 201A. Both the BK 3A and the BZR201A share the same electrical parameters and winding ratio, such as 1.6-1.8Ω primary resistance and a 72:1 ratio. (The bottom label mentions that you need to use a 0.8Ω ballast resistor, so maybe that was mixed up with the primary resistance by the author of the Alfa Romeo book).

    If you need to replace a BK 3A, either use a BRZ201A (thats the one with the large golden Superpotente sticker at the bottom) or a Bosch Red coil (coil 0 221 119 030). The Bosch Red has a winding ratio of 82:1, so the output voltage would even be ~10% higher than with the BK 3A.

    Regards,
    Adrian
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  8. Ferraripilot

    Ferraripilot F1 World Champ
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    I use the BOsch red coils and they are fantastic. Thanks for the clarification! Most appreciated
     
  9. parkerfe

    parkerfe F1 World Champ

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    I replaced my MM ignition and coil with MSD including a black Blaster coil, put a MM coil sticker on it and it looks just like the OEM MM coil and performs better.
     
  10. hutchGTB

    hutchGTB Rookie

    Nov 10, 2010
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  11. f355spider

    f355spider F1 World Champ
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    Interesting, when I had the Crane Cams electronic ignition installed on my (USA) 78 308GTS, the technician used Bosch blue coils, and it worked beautifully, with quick, clean starts everytime. He had done literally dozens of these conversions on 308s, 246's and many V12 Ferraris.

    What are the primary differences between the Bosch blue and red coils?
     
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  13. alhbln

    alhbln Formula 3
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    The Bosch Blue coil has a 50:1 ratio and just 15-18kv secondary output, it does not require an external resistor as the primary wiring is around 3.6 ohm. This is the coil with the lowest output from the Bosch range, it will work well with a low compression four cylinder engine but i wouldn't recommend it for a sports car. With a points setup use the Bosch Red coil instead.
     
  14. f355spider

    f355spider F1 World Champ
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    I guess my question is whether the blue coil was appropriate with the Crane Cams electronic ignition conversion, which removed the points...I would assume so.
     
  15. BigTex

    BigTex Seven Time F1 World Champ
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    It's interesting to me that on all those older oil filled coils they ALL say not to mount horizontally.......well......Ferrari did!

    I used the solid potted high vibration MSD units last time I purchased, it's labeled "any orientation" mounting wise.....
     
  16. alhbln

    alhbln Formula 3
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    The blue coil will work with all the Crane points conversions (XR-i/XR600/XR3000) but its not an ideal setup for a Ferrari due to the blue coils low output. By using a coil with a higher winding ratio such as the Red Bosch coil or Marelli BZR 201A you will see a more complete combustion, especially at higher revs and less fouling of your spark plugs.
     
  17. alberto

    alberto Formula 3
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    Excellent posts/information.

    My guess is that the BK3A coil commands the price they do just because of the cosmetics; they retain the OEM look.

    So even for electronic ignition conversions you would recommend the Bosch red coils?

    Is there a coil that maintains the vintage look, is not ridiculously expensive and has good performance?
     
  18. alhbln

    alhbln Formula 3
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    I would recommend the Bosch Red coil only for points based ignitions as well as for electronic conversions which expect a coil for points based setups (Crane XR, Pertronix Ignitor, Lumenition, Superformance Dinoplex Replica etc).
    High power electronic transistor ignitions such as the Bosch 137/139 system which handle 8A at the primary side of the coil require a special high performance coil, though.
    The same goes for capacitive ignitions (Dinoplex, MSD 6, Crane Hi-6, Mallory Hyfire) which need a special 'transformer' coil to step up the capacitive discharge.

    By painting any of the coils in a satin matte black finish and applying a replica label you usually get quite close to the original vintage look. I can post some photos in a week when i am back home.
     

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