ORIGINAL: liquid_TR
It takes MORE power to fire thru higher pressure in the combustion chamber.
Well thats not really true, as the total coil turn ratio is probably around 1:4000 to actually turn 5V DC into AC and step it up to 20KV. (its actually made by first stepping up the 5V DC into a much higher potential AC by means of a small inverter in the ignition unit then stepping up that AC potential up to 20KV).
10KV can jump thru a couple of centimeters creating an arc discharge. there would be not much of a difference between using a 6V pack or 3.7V pack. both will create a suitable arc if they were stepped up directly without loss. The main reason the ignition unit wouldnt work below 3-2V DC is the inverter side electronics are actually cant work with such low voltages. If the transistors were chosen to work with those low voltages, we wouldnt have any problems using a single nicd cell. This is my theory. I actually never opened up a chinese ignition unit.
Model ignitions are pretty low power requirement devices tho voltage on typical ignitions is 15000+ .
BUT it always takes more power to fire thru higher pressures.
This is why extremely high output ignitions were developed -for competition engines.
Most applications in passenger cars etc., neded high voltage with little amps - The gap plus the pressure is the condition which must be met.
For those doubters -once apon a time Champion Spark plug sold spark plug cleaners which were used in service stations and the customer could clean their spark plugs with these devices
a feature was adjustable pressure in th chamber which would show if the plug still fired under high pressure
High pressure being upwards of 100PSI
Most cars of the period had cranking pressures of over 100 psi so that always bugged me -I guess they used a very weak spark in th Champion Spark Plug Cleaner.