I have been reading this article many times over:

http://www.corvetteforum.net/c4/doctorj/heicoilinfo.htm

I think I understand the basics, or at least the conclusions. One nagging question I have is this: does an ignition module with a higher amperage limit charge the coil more quickly? I know from the article that it can achieve a higher TOTAL energy, but does the slope of the charging line change if you change the amperage limit on the module?

Reason for my confusion is an apparent contradiction between these two things in the article:

Quote: "The extra current from the aftermarket modules by itself won't do anything special for the engine, but it allows FASTER COIL SATURATION & greater stored energy in the coil." (Caps added by me)

Further down there is a "sawtooth" graph showing coil saturation vs. time. Shorter the time, less chance of the coil reaching saturation. Clearly the line slopes up at some constant rate (determined by coil properties and supplied voltage?) until it hits the module's current limit and then BAM!- the party's abruptly over. That's as far as you go.

It would appear to a casual reader like myself that the amperage limit of the module would NOT affect how QUICKLY the coil carges, just how how high you can GO before the coil has achieved as much potential energy as the module will let it have.

Any clarification that you EE-types could offer would be much appreciated. Use small words. I also like shiny things and sometimes drool from the corner of my mouth.

 

Unless you have an engine that needs a better spark, a stock ignition works fine. High compression engines or any engine with a power adder should have a better spark and usually all you need is a better coil.

When I still used a SBC, I had a factory large cap HEI distributor. The only thing I changed was to install the Accel in-cap Super Coil. I was shifting at 7000 rpm and never had an ignition problem.

 

Both the maximum current and the charging rate are ultimately limited by the coil; the first by the DC resistance of the coil and its connections, the second by the combination of coil resistance and inductance (collectively known as impedance). Battery voltage also plays a role, but we'll assume that's a constant The ignition module can only limit the rate of current increase and the maximum current; it cannot do anything to force the coil to charge any faster.

Increasing the coil energy comes through either more inductance or more current. Increasing inductance also slows down the recharging time so it's a compromise. Increasing the current causes more heat to be dissipated, especially at low duty cycles with long dwell times (i.e. low engine speeds). The second issue can be addressed to some extent by a variable-rate module, such as stock GM HEI modules, but there's still limits - as drive current increases, the resistance of any connections in the system become more significant, and the cost of the drive circuitry increases.

 

Thanks very much to you both. That's what I thought the answer would be. My experience is that changing the coil is your best bang for the buck. Changing the module does little. Now I know why- the coil can only charge so fast, no matter what the module does. Stock coils can't charge very fast so when you get high up in the RPM range the coil is being asked to discharge long before they have even reached saturation (fully charged) because the time between firings gets so short. The spark gets weaker and weaker as the RPMs rise. A coil that can charge more quickly (aftermarket) may not have any more energy than a stock coil, possibly even less depending on the design, but it's doesn't fall off as quickly in the upper RPMs becuase it can reach saturation more quickly than a stock coil.