I have no "beef" with your friend. He is not the one who posted the original information. You posted it, and I'm merely disagreeing with the technical accuracy of the information you provided.

I invite correction if you see any technical inaccuracies in my post.

 

I think we are in agreement that the purpose of the shunt contacts in the solenoid, which temporarily remove the ballast resistor from the circuit, is to generate a hotter spark during cranking.

Once the engine is running and the ballast resistor has been re-inserted in the circuit, I think the ballast resistor definitely reduces the arcing damage to the points. In a series R-L circuit, there is little or no arcing when the points close. The current starts at zero and ramps up slowly due to the inductance of the coil.

The major arcing event is when the points open and interrupt the DC current flowing in the primary winding of the coil. The flux field in the coil collapses quickly and induces very large voltages in both the secondary winding (spark for the plugs) and in the primary winding (arcing across the points as they begin to open).

The arcing damage to the points is proportional to the DC current that was passing through the primary winding at the moment just before the points open. The ballast resistor reduces the primary winding current by a significant amount compared to what the current would be with a full 12V applied to the primary winding. This reduces the arcing damage to the points.

It's worth noting that early in the 1963 C2 production year, the nominal resistance of the production ballast resistor was something like 0.3 ohms. In later production, it was changed to nominally 1.8 ohms.

I believe that GM issued a Service Bulletin to address customer complaints about having to replace points at frequent intervals in early 1963 Corvettes. The Service Bulletin recommended that dealers replace the 0.3 ohm ballast resistor with the 1.8 ohm ballast resistor.

 

So here is a question for you experts. Does it do any good to use a ballist resistor with the factory K66 ignition?

 

You should use K66 the way that GM's engineers designed it.

I have read that the K66 transistorized ignition did not use a ballast resistor, but I have not independently confirmed that.

 

If you look at the TI system schematic, it already has two ballast resistors in the harness.

 

I don't necessarily agree that the shunt circuit is there to generate a "hotter spark" during cranking. I suspect that the shunt circuit could be disconnected from most of our fair weather toys, and our antiques would start up just fine. I contend that the circuit is there to restore, not increase, the spark energy during low battery voltage cranking conditions.

 

I think we are saying the same thing in different ways. Eliminating the ballast resistor during cranking absolutely, positively creates a "hotter spark" than would be created with the ballast resistor in the circuit. This cannot be disputed.

What can be disputed is the reason why GM thought this feature was necessary. I have no direct knowledge of what the GM engineers were thinkng when they added this feature. All I can say is that they probably had a good reason, because in the 1960s GM was very cost conscious and they did not add cost to their designs unless they has a good reason to do so.

 

I'm not disputing the circuit physics. I'm disputing the reason often tendered here for the inclusion of the circuit.

"Hotter" spark is not needed during normal battery voltage cranking operation. But compensation for low battery voltage is needed during cold weather cranking.

 

I have a new wiring harness. Do you know if the new one have them?

 

I do not know what the GM designers were thinking when they came up with the C2 design that included a ballast resistor that was shorted out during cranking. All I can do is look at their design and use basic engineering analysis to figure out the effect that this design had. The effect was to produce a hotter spark during cranking, regardless of what the ambient temperature was at the time. An additional feature was longer life for the points.

Unless you were on the design team or you have read papers written by the design team, I think it is mere speculation to say that you know what they were thinking when they added this feature. And, it's probably not important anyway. The design speaks for itself. They wanted a hotter spark during cranking.

 

Thanks, Dan, for posting John Grady's piece on ballast resistors. This is the type of information that provides good reference information for Forum members.

 

Yes , thank you for the post, Always glad to receive new knowledge and context.

 

I thought it was/is O’Hare field/ airport , named after Butch O’Hare a WWII Navy pilot and Congressional Medal of Honor recipient- for his achievements in shooting down Japanese aircraft at the battle of Midway.

 

Have been running Petronix without ballast resistor in my ‘64 L76 for 4 years
No problems

 

I'm not very familiar with the Pertronix system, but I think I have heard that Pertronics requires elimination of the ballast resistor because their electronics relies on a full 12V supply at all times. Do they also require the use of a different coil?

It would seem to me that the original factory coil would overheat with a full-time 12V supply.

 

I was told by old-time farmers that when converting an older 6V vehicle to a 12V, if you didn't add a ballast resistor to the coil circuit the service life of the points and coil would be shortened. I learned this the hard way in my youth converting a number of older Tractors and Dodge trucks, including a D600 4x4 that stranded me in the desert when the point pads in it's flathead six burned completely off. Reading the physics reinforces the words of wisdom (thanks).

 

Tux:

I was tired when I posted, and my spelling was in the toilet. I should be better than that.

Butch did his flying in the F4F Wildcat. I did mine back then in a big block MOPAR.

Larry

 

If it's built correctly the ballast resistor wires should be part of the harness.

 

I gotta commend the both of you for providing some entertaining reading. As long as you each have a self-consistent mental model of the ignition circuit behavior, you are both right.

Sort of like is it positive electricity flow of negative electricity flow. It doesn't matter as long as your equations are consistent.

BTW, I'm also a EE.

 

OK, my head is spinning and I feel I understand less now than before I started on this thread. My question may be the most basic given the above info and could certainly be contained in what has already been said, but here goes anyway:

My '67's ballast resistor is more than likely the factory original. It's supposed to be rated at 1.8 ohm but meters out at 2.3 ohm. Is this significant to any degree and (really basic question) how does higher ohm resistor affect coil performance and spark production characteristics in an engine's operating range?