Car Question: Differences in Ignition Coils

Car Stuff Link for Excel Ignition Coils

Can someone who understands the ignition part of a car engine explain the difference between these 4 coils? I understand that there are differences in resistance and voltage, but what difference are they actually going to make in the running of the engine?

I was considering one of these high-end Excel coils because I have a hard time starting the car and keeping it running sometimes and it has the original coil on it. I know this makes a difference in certain situations.


This site explains the basic principle of the ignition coil. The coils listed in your link can provide more voltage than the stock coil, in theory making your car run better but they are really designed for cars with modified engines and ignition systems. I have found that using a more powerful coil can accentuate problems rather that fix them. If your car is older and uses breaker points, they will wear out quicker. If the car is having fuel delivery problems, a more powerful coil will cause the car to run worse. If the coil in your car is good, you would be better off investing your money on improving the starting and idling situation rather than throwing money away on a new coil.

The simple answer?
One is black
One is yellow
One is chrome
the fourth one is yellow and square, making it hard to mount in the original location. :smiley:
Look here’s the deal. Back in the day of conventional ignition systems coils came in two flavors, ones that were designed for an external ballast resistor, and those that had the ballast resistor built in. The ballast resistor was there to limit the current to the points so that they had a chance to last 12,000 miles.
So what’s the deal with high performance coils?
Well if we were to put your '66 Muchwang on an ignition scope we would see that the secondary voltage is about 9-11KV at idle. If we then screw one of these super coils on the car and re-scope it. What do you think we will see for secondary voltage at idle? If you guessed 45KV you would be wrong. If you guesses 9-11KV you would be right. Why is that? The coil is only going to produce only enough voltage to ionize the gap in the spark plug. No more. Now under some other conditions the coil will need to produce more voltage (typically during a hard acceleration) but very rarely will a coil need to produce more than 20KV on a conventional system
Now let’s talk about your problem. Do coils go bad? Yes sometimes they do. A '66 car is forty years old. Could the coil be bad? Sure. Is this the most likely suspect in a hard start / poor idle complaint? No, there are lots of things I would look at first.
Does your car still have points in the distributor? Is the dwell set to spec? Is there dwell variation when the car engine is reved? What is the timing set to? Is the mixture too rich or too lean? Vacuum leaks? What is the condition of the cap / rotor and plug wires? How old are the plugs?
After I was satisfied that all of the above was right, then I might consider a new coil…

PS the chrome one adds 10 show power to your car.


Here’s the problem.

One day while sitting in heavy traffic for an hour or so, I’d occasionally feel a “miss”. Not like it wasn’t hitting on all 6 cylinders, but more like a complete loss of power for half a second. For a while, it wasn’t enough to kill the engine. Then it died. I got it started again and spent about 30 minutes using both feet and keeping the idle up a little bit (it had gotten dark and I was without a flashlight, otherwise I would’ve stepped the idle up a hair).

There was no loss of power when accelerating and no dimming of the headlights when it missed.

For some reason, which escapes me now, I concluded that the coil was weak.

The car has about 1000 miles on it since the engine was rebuilt. The previous owner had it rebuilt about 6 months before I bought it and it hasn’t been driven much.

It’s possible the points and condenser and other ignition stuff was never changed or set right.

I’m not sure how to set the points. I do have an ancient ignition kit that my dad gave me that has the little tools for making that adjustment. I guess it’s worth a shot. I’ll have to find out what the correct specs are for that car.

Thanks for the reply.

WAG $22.14? :wink:

Based on your deescription, I don’t think it’s a coil problem.
I would look at the carb idle circuit, vacuum leaks, general ignition system (wires, plugs cap rotor, and dwell)
Good luck