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Quote:
Originally Posted by 40 Deluxe
Jim, How much voltage can a helmet rotor handle, in case a guy runs higher cylinder pressure or larger plug gaps? It's been my understanding (could easily be wrong) that these rotors can short to the shaft if subjected to higher voltage,like a "hot" coil or a 12 v. coil can produce.
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Goodpoint as thats always a concern in these old ignition systems . I made a tester once from a old NAPA Echlin training manual showing how to test Flathead helmet rotors using a coil set up to check for shorts.
Every rotor i tested showed shorted !!!!! A rule of thumb is you cant STOP secondary voltage ( you can prove this theory with a scope) if the voltage is high enough it WILL GO TO GROUND , you may not know where but it will go to ground.
The only thing you can do is
control it , it will always take the least path of resistance . So keep the shaft insulated with shring tube , use good connectors, and good plastics should be ok. Even though we feel as if the engine mods are drastic , most flatheads use very low compression ratios and overly rich air fuel ratios....
Stay tuned as i am gearing up for some live engine testing with a lab scope this winter......
As far as a hot coil is concerned a coil will only produce what the engine asks for . The compression ratio may ask for extra but the three carbs ( maybe rich) will ask for less and the trade off may be just normal spark is needed .....