[jbrewer]

That's helpful...

V in any inductor is proportional to di/dt ...the change of current with respect to time. Multiply (inductance of the primary) x (di/dt) x (turns ratio) to get the voltage in the secondary.


So it would make sense that you've gotta make a big di/dt to get a big voltage in the secondary (or have a really big turns ratio) to jump the air gap of the plug.



So that makes sense.

LOAD of the engine makes no difference to this heating (other that convection) as it's simply a function of the RPM of the motor and the gap in the secondary.



Thanks for helping me though this.


Trying to remember which old cars used a resistor block (I know Chevrolets did) and which didn't....and why. As I recall , the resistor was in series with the primary of the coil, which would serve as a current limiter.