Re: Mallory tech answer to coil/ballast ?
 

Thanks, I will do that test tomorrow.

I should also mention that there were a 1.4 ohms coil and a 0.7 ballast resistor when I bought the car. When the car died that time on the highway (4 years after I bought it) I changed to a 0.7 MSD coil and a 0.7 resistor. It worked fine for 3 more years and then it happened many times this summer, during very hot summer days.

So to change to 1.4 ohms coil and skip the external resistor is more or less going back to the original setting and taking it a little bit further. I did not know that coil could have different ohms untill last week. At some point I think there has been a breakerless setting on this car. There is a lot of wires that are not really going anywhere.

Re: Mallory tech answer to coil/ballast ?
 

Attached is what you should get for voltages and currents for the 12v, engine off case with R loom=1.5, R ballast = .7, R coil = 1.4. If you want other cases let me know.

Re: Mallory tech answer to coil/ballast ?
 

Thanks for all the support. I have two more questions:

According to MSD, the resistance is suppose to increase in the 0.7 ballast resistor (some sources say up to 1.4 ohms) when the engine is hot. How does that effect my voltage? (Perhaps you already explained this and I did not quite get it?) What would happen if I put in a 1.4 ohms ballast resistor instead of the 0.7, combined with a 1.4 ohms coil and kept the 1.5 ohms "wire resistance"?

The only thing that I changed on the car this year was to a leaner air fuel mixture since I had to high CO. Bubba wrote something that rich air fuel takes less and lean air fuel takes more voltage. Could this affect the "voltage need" in my car?

Re: Mallory tech answer to coil/ballast ?
 

What coil do you have MSD 8203 ,
calls for a .8 OHM resister MDS coils 5 6 7.
If you put a 1.5 in stead of .7 plus wire 1.4 ohm that is the same as 2.9 total
if you had 2 amps that's about 6 volt only 6 left for coil.
more resistance is less amp.
so 2 amp .8= 1.6 leaving10 volt at coil
so 4amps.8=3.2 leaving 8.8 at coil.
(AS I said lose the wire ohms) and use what they said .8ohms/.7ohms.
Ask msd if its ok to use a wire resister with there .7ohm resister. that's a total of 2.2 at 2 amps thaths 4.4 = 7.6 ,4 amps is 8.8 leaving 3.2 volts at coil.

Re: Mallory tech answer to coil/ballast ?
 

As requested, for .7 and 1.4 ohm ballast ... slight modification on the first one from post 82. Current drops from 3.3 to 2.8A with ballast change

Re: Mallory tech answer to coil/ballast ?
 

good job on the charts , can we see one with a 12 volt, 1.5 ballast and a 1.5 coil ????

Thanks

Re: Mallory tech answer to coil/ballast ?
 

AS requested for 1.5 ohm ballast, 1.5 ohm coil, and no loom resistor. Added engine running case with points closed for peak voltages and currents. These need to be averaged by the dwell to get average voltages and currents.

Re: Mallory tech answer to coil/ballast ?
 

This is great and easy to overview!

Can you post one with 12v, 1.5 ohms loom/wiring and 1.4 ohms coil and no ballast? (Perhaps, you already did this and I apologize if I missed it).

It seems like voltage to point is the same (0.1v)? What would be the maximum volt at coil and still have 0.1v at points?

Re: Mallory tech answer to coil/ballast ?
 

Ideally the voltage at (across) the points would be zero, if they were a "perfect" switch, with 0 ohms resistance. The coil voltage will not impact the voltage at the points significantly. I put a max of 0.1 volts to indicate that they are not badly pitted and have not become high resistance.

For instance if the points had 0.1v across them, with 4A flowing through them, the contact resistance would be 0.1/4=.025 ohms (25 milliohms) which is still pretty low. I am reading about 0.03 V on mine at 4A = 7.5 milliohms.

The lower the better. If you see this voltage creeping up to a volt or so over time, the points are likely ready for a good cleanup or replacement. Maybe Bubba can comment on the points numbers.

Here is the request slide with no ballast. The numbers are virtually the same, as the ballast has been replaced with the loom, but the totals are the same

Re: Mallory tech answer to coil/ballast ?
 

Here's the requested slide

Re: Mallory tech answer to coil/ballast ?
 

Many thanks!

So according to this it would do no harm to the points and therefore it would be ok to skip the ballast resistor?

I will do the test as soon as I get my analog multimeter that I bought on ebay.

Re: Mallory tech answer to coil/ballast ?
 

Looks fine to me. Be sure to check the actual numbers with measurements to be sure.

With the engine off, the dissipation in the loom resistor will be about 25W (6.16V x 4.1A) …. That’s quite a lot of heat. How long is it, and where is it located? Is this an original part on the car, or an add on?

With the engine running, the power will be reduced to around 14W average because of the points opening and closing.

Re: Mallory tech answer to coil/ballast ?
 

Hello again!

I got my analogue multimeter and it measured 8.2 volt on the positive side of the coil during idle. I am satisfied with that and therefore I am gonna keep the ballast resistor. The car is also running great.

However, I do 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?