Ignition System Questions

Hey guys, I have a few questions regarding distributor type ignition systems.

After having done some research, I found that resistor spark plugs and plug leads are used to reduce noise..?
"Hotter" spark gives out a better combustion..

On conventional type distributors (breaker type), non-resistive spark plugs and solid copper core leads can be used as there are no electronics;
But on electronic distributors (with an ignition module), resistor spark plugs and resistive plug leads must be used.

Questions are:
1. On electronic distributors, does the "noise" interfere with the ignition module?

2. Does resistive plug leads have to be used with resistor spark plugs? Cant a solid copper core plug lead be used to create a "hotter" spark for better combustion?

3. I have a Haynes manual of a vehicle (electronic type distributor), on the ignition section of the manual, it ONLY states the MAXIMUM resistance of the HT LEADS which is "17500 Ohms maximum per lead" (resistor type spark plug mentioned). Does this mean that this vehicle can operate with plug leads with little to no resistance?

4. Can a plug lead with a little to no resistance cause drivability issues? I have only seen information were there is either excessive resistance or an open in plug leads, nobody has ever mentioned anything about resistance being too low.

5. The coil lead from the ignition coil to the distributor cap is also a "HT Lead", does the 17500 Ohms also apply or is it suppose to have less resistance than the plug leads? The coil lead is generally way shorter than plug leads.. (The manual does not state a separate resistance for the coil lead)

6. How does one calculate/choose the correct heat range of spark plugs? Besides going back to a workshop/repair manual, for instance the vehicle is modified.

7. Is there a decent rule of thumb that one can follow to measure the resistance on resistive and non-resistive HT Leads? (Too many figures have been noticed in my research)

All input welcome

Sent from my SM-G531H using Tapatalk

A lot of questions.
As long as an a high tension spark plug wire dosen't have an open or short the ressistance of the path from the coil to the tip of the spark plug has to all intents and purposes zero effect on the energy of the spark. Suppressed ignition HT leads have been mandatory for nearly 60 years long before solid state electronics were fitted to cars.
The only real downside to carbon fillament spark plug leads is on some types the carbon fibres can be easily damaged by heat and vibration or during servicing resulting in an open. This is less of a problem than it used to be for two reasons; the quailty of ignition leads has greatly improved and we no longer have to service the ignition system every 5,000 miles.

If a carbon fillament spark plug wire has an end to end ressistance of 3,000 to 17,000 ohms ( depending on length) and passes a water spray short to ground test then it is a good wire. --- Paul made a good video on I will see if I can find it and post a link.

The engergy available for the spark is essentially controlled by two things, the energy stored in the coil and the spark plug gap (and other spark gaps the ignition HT current crosses enroute to the spark plug).

The high tension (secondary) ignition voltage is control by spark plug gap and conditions inside the cylinder. The wider the spark plug gap the higher the secondary voltage.
Wide spark pug gaps greatly increase the output HT voltage demand on the ignition secondary this has both advantages and disadvantages. The advantage is a the longer spark ignites more of the fuel air mixture and is more likely to fire a fouled spark plug the huge disadavantage is it places a huge electrical stress on the insulation of the coil and plug wires so is much more likely to result in a short to ground especially in damp conditions, also because the coil can only produce a given ammount of energy if the secondary voltage demand increases the time duration of the spark is reduced.

Anything that changes conditions inside the cylinder also have a major effect on the spark plug voltage including lean mixture, compression pressure, fuel type (ie LPG or CNG), and ambient humidity. For example when runing an engine on LPG or CNG it is normal practice to reduce the spark plug gap by 10 to 20 percent to ensure a reliable spark and protect the insulation of the coil.

In short you won't find any extra power by fitting wire leads or fancy coils and if you do you may introduce reliability issues so my advice just stick to using either OEM or good quality Silicone ignition leads.

I don't have time this morning to explore spark plugs --- really a huge subject on its' own I will get back to give some info on selecting spark plug heat range and electrode types.