'57 Ballast Resistor - NCRS Discussion Boards

'57 Ballast Resistor

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  • Art B.
    Expired
    • July 31, 1989
    • 333

    '57 Ballast Resistor

    The ceramic on my ballast resistor was cracked so I decided to replace it. I purchased a Delco Remy replacement that I purchased at a local Corvette parts store. When I took it out for a drive, it started fine but would barely run. It felt like it was firing on about 4 cylinders. I replaced the resistor with my old one and everything was fine again. I measured the resistance with a digital ohmeter and found that my old one had about 1.7 ohms while the new replacement had only about 0.6 ohms. On the ceramic is stamped 0.2 ohms.
    Why would the replacement resistor cause the ignition problems?
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15610

    #2
    Re: '57 Ballast Resistor

    Up to 1964 Corvettes had two different ballast resistors - approx 0.3 and 1.8 ohms. Each ballast had a specific coil, and the low resistance ballast was generally used on mechanical lifter engines in order to achieve higher primary current for more igntion energy.

    This caused problems with point burning, particularly in cold weather, and 1964 was the last year the 0.3 ohm ballast was used.

    You should check your AIM to see which ballast/coil was used for your engine. Assuming it was the 1.8 ohm version, you should replace it with a 1.8 ohm version. The commonly available replacement ballasts are all 1.8 ohm as far as I know, so any of these would be functionally correct, but not visually correct.

    The above does not explain why the engine runs poorly with the new ballast. I would expect it to run fine, but have a higher tendency to burn points.

    Duke

    Comment

    • Jack H.
      Extremely Frequent Poster
      • April 1, 1990
      • 9906

      #3
      Re: '57 Ballast Resistor

      Factory original ignition for '57 used either an '091 coil (carb engine) or a '107 coil (FI) but the same, low resistance ballast, 1931385 was used with them. Nominally, this ballast was rated at 0.3-ohms although 0.2-ohms is within factory spec deviation profile. The current reproduction of the '385 ballast (Shafer) matches the GM service replacement profile of the factory original ballast resistors (different ceramic from what was used on your '57 + subtle difference in mounting band) and they're known to work well.

      Later, in the '63 era, the ignition system changed to buy more durability between tune-ups. Engines with hydraulic lifters used an '087 coil (changed to '202 coil around '65) and 'hot' engines with solid lifters continued to use the '091 coil. There were other coils used for 'exotic' engine applications such as FI, TI, and BB, but that's another story. The '091 coil equipped engines continued to use the 0.3-ohm, 1931385 ballast. The '087/'202 coils used a higher resistance ballast, 1957154, rated at 1.8-ohm nominal.

      The ballast you use should match the primary winding characteristics of your ignition coil. You said the ballast you replaced measured 1.7-ohms which is close enough given the precision of the ohm-meter you're using to confirm it was a 1957154 which indicates it was NOT the car's factory original ballast to start with! This makes me believe your coil is most likely NOT a factory original '091....

      You could be running the primary side of the coil SO HOT with the 0.3-ohm ballast that you're saturating the core and distroting the secondary spark waveform. Or, your coil may be fatigued from prior use such that the core laminations are separating and it can no longer handle its factory original rated magnetic flux traffic.

      That'd be my educated guess...

      Comment

      • Clem Z.
        Expired
        • January 1, 2006
        • 9427

        #4
        Re: '57 Ballast Resistor

        jumper the the working resistor to see if the car acts the same as the replacment one,if it does you have found your problem,to much voltage to the coil BUT if it runs OK the problem is the new resistor is defective. back in those days we always wired a bypass around the resistor thru a switch so if we pick up a race we would have full coil voltage to the engine and i never had the problem you are discribing having higher voltage to the coil

        Comment

        • Art B.
          Expired
          • July 31, 1989
          • 333

          #5
          Re: '57 Ballast Resistor

          Thanks to all three of you for your responses. I have an 091 coil on the car and I have the 2x4 carb setup. Clem, I jumpered the resistor and the engine immediately ran rough and backfired.

          Comment

          • Clem Z.
            Expired
            • January 1, 2006
            • 9427

            #6
            Re: '57 Ballast Resistor

            sounds like a bad coil to me because when you are cranking the engine over you are by passing the resistor.

            Comment

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