Legacy cable length in a grid

Discussion in 'PSI Superchargers Tech Questions' started by PROMOD63, Dec 2, 2016.

  1. PROMOD63

    PROMOD63 Member

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    Moving the grid around and need to lengthen the legacy cable from the rpm output on the mag box to the gridcis this gonna cause issues ?
     
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    PROMOD63, Dec 2, 2016
  2. Mike Canter

    Mike Canter Top Dragster
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    Do you mean the wire that goes to the rpm chip plug on the Electonic Points Box? If you lengthen that the you change the resistance in the wire which in turn change what the rpm limit the Points Box sees. It may only be a small amount of change and you can test it by setting the high limit rpm to a low setting like 3000 or 4000 rpm and rev the engine up and see what happens
     
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    Mike Canter, Dec 2, 2016
  3. PROMOD63

    PROMOD63 Member

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    Is this only for high side Rev limit or does this wire do more than that ? If it's only for high end Rev limit could I just use a chip and not hook it to the grid ?
     
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    PROMOD63, Dec 3, 2016
  4. Critical Mass

    Critical Mass Member

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    This is very good question. These are the two yellow wires that go to the RPM chip plug in the box. You would think as long as you match the resistance of the two original yellow wires you should be able to make them any length that you want?
    Also, what about the white wire that goes to the mag.? I believe this one isn't as sensitive as the two yellow wires?
    Joe
     
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    Critical Mass, Dec 3, 2016
  5. Torment

    Torment Member

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    With my MSD 10+ using the legacy cable for the 2 step rev limiter gave a very rough sounding rev limiter. I unplugged it and use a chip - much smoother rev limit. The cable was only for the rev limit, no negative in not using it - other than a chip is non-adjustable, unless you have more chips...
     
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    Torment, Dec 3, 2016
  6. Jon Sandahl

    Jon Sandahl New Member

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    I extended the 2 yellow wires on 3 Roots pro mods that had the Grids mounted on the door bars and never had an issue, 2 step worked where is was set to in all cars.
     
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    Jon Sandahl, Dec 3, 2016
  7. Critical Mass

    Critical Mass Member

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    Promod63,

    I measured the resistance of a 9000rpm module, 4000rpm module and the two yellow wires.
    9000rpm = 8300 ohms
    4000rpm = 2700 ohms
    two yellow wire in series = 0.0 ohms

    I now agree with Jon Sandahl. Extending the wire a few feet should not make any difference. The resistance of the rpm module is the dominate factor.
    Thanks, Joe
     
    #7
    Critical Mass, Dec 3, 2016

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