Ideal voltage to positive side on coil when using points?

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08-23-2013, 03:18 PM

#21

jlg2002

4th Gear Member

Join Date: Jun 2006

Location: Fontana, California

Posts: 1,483

Quote:

Originally Posted by Gasoline

Hello!

I have a old fashioned Mallory with dual points, Accel 1.4 ohms coil and 0.7 ballast resistor (and probably a wire resistance from the ignition).

I have 13 volt on battery and 14 volt when engine running. The results are:

With no resistor: 9 voltage on positive side on coil when running and 5.7 voltage when key on and motor off.
With resistor: 8 voltage on positive side on coil when running and 4.7 voltage when key on and motor off.

I had problems with the car shaking/dying during hot summer days and the results above were much worse when I used a 0.7 ohms MSD blaster so I changed to 1.4 Accel and they improved. Should I also skip the ballast resistor or not? Is 9 voltage to much? I do not want to burn the breaker points.

Lets discuss why the ballast resistor is there- it's there to maximize the life of the coil due to overheating (work) from the amperage flow trough it and the points. Ohms law states there is a specific relationship between voltage (E), amperage (I) and resistance(R) E=I*R. These same quantities are also used to define power (P[Watts]=E*I ) which is the definition of work (which in our case results in heat). As the voltage or resistance changes so does the amperage and all terms affect the power dissipation.

Now back to your question, if you are using the factory dist lead wire and the ballast resistor you are dropping more voltage than is necessary. ( as you've already noticed how low the voltage goes). Ideally 7-9 volts on the + side of the coil is plenty for a street car. You can also use a straight 12V-racers can use 12 V all day long to get the best performance but it takes special coils to do so. To close- look for a coil that is designed to run 12V and use it if you want the best performance. In the day, ACCEL were the ignition parts to use for best performance.

08-24-2013, 10:58 PM

#22

fastbackford351

Foghorn Leghorn

Join Date: Dec 2006

Location: I reside in a near constant state of amazment.

Posts: 2,923

I enjoyed reading that.

08-26-2013, 08:32 AM

#23

Gasoline

1st Gear Member

Thread Starter

Join Date: Sep 2009

Location: Arizona

Posts: 74

Great, but then I wonder: Would it make any difference, performance wise, if there were 7, 8 or 9 volt at the positive side of the coil? For example under load?