resistor and non resistor spark plugs

MexicoMike said:

FWIW - there is no "hotter" or "more powerful" spark. The spark delivered is whatever it takes to jump the gap, which varies with engine load. IOW, if you have an ignition system that is capable of delivering, say, 50k volts, and it takes 15k volts to jump the gap, 15k volts is the "spark" that is delivered. IF there is enough voltage to jump the gap, the "extra" voltage does nothing to "increase" the power/heat of the spark. What a higher voltage secondary DOES do is allow the spark to jump larger gaps which reduces maintenance, increases the ability to fire though fouling, and allows a larger gap to be run.

Let's say you are running suppression wires AND suppression plugs. If the system can generate the spark to jump the gap at all phase of engine load, then replacing the wires/plugs (both or either) with non-suppressed components will make absolutely no difference.

Click to expand...

You are correct. htown16, note that the OP states he has a magneto ignition system. These require the reduced spark plug gap, due to their relatively poor ignition performance at kick start engine speeds. So for him, using a resistor plug could very well be an issue. Using a resistor spark plug on CDI ignitions, where one is not specified may also cause issues. It's not really a big deal on a Kettering [aka points and condenser] ignition or an inductance electronic ignition system, unless you have a failing ignition coil.

MexicoMike said:

FWIW - there is no "hotter" or "more powerful" spark. The spark delivered is whatever it takes to jump the gap, which varies with engine load. IOW, if you have an ignition system that is capable of delivering, say, 50k volts, and it takes 15k volts to jump the gap, 15k volts is the "spark" that is delivered. IF there is enough voltage to jump the gap, the "extra" voltage does nothing to "increase" the power/heat of the spark. What a higher voltage secondary DOES do is allow the spark to jump larger gaps which reduces maintenance, increases the ability to fire though fouling, and allows a larger gap to be run.

Click to expand...

There's more to it than that. A spark is a high temperature, luminescent column of ionized gas. Once the gap is bridged the gas between the electrodes ionizes and the voltage drops to a few hundred volts. During the next millisecond or two the spark is maintained until the stored energy in the coil dissipates to a level where the spark can no longer be sustained. That millisecond is when the energy in the spark delivers the HEAT required to ignite the mixture. The wider the gap the more voltage is required to jump it, but the size of the spark and it's exposure to the combustion chamber also increases. A "hotter" or "more powerful" spark would be one that is physically larger (gap distance) and / or lasts longer (duration). The latter is a function of the stored energy (current squared times inductance) in the coil. The point here is that it's not just voltage, but energy that defines a spark.

Case in point, GM developed their HEI ignition around 1975. For the 1986 model year they discovered that they could meet current emissions requirements just by increasing the plug gap from .060 to .080. The larger spark exposed more surface area to the combustion chamber resulting in more complete ignition and lower hydrocarbon emissions.

maylar said:

A spark is a high temperature, luminescent column of ionized gas.

Click to expand...

Actual name is plasma. also in electric welding
As previously mentioned by MM
Spark plug gap for magneto's if reduced by the book, to .015 will result in max 4-6KV to start the combustion and then idle.

When the throttle is opened and cylinder pressure goes up the voltage requirement can approach 15KV to create the plasma for ignition. Any capability in excess is mainly academic like emissions or non standard HIGH compression/pressures ETC,

fiatfan said:

Details on the NGK plug Schwany mentioned. They say the center electrode is "non-projected". Is that right?

View attachment 22005

Click to expand...

Yes, they are non-projected and use a 5/8" wrench. The center electrode is above, but close to flush with the end of the threads. The side and center electrodes do not go into the combustion chamber as far as a BP7ES. They are about 1/16" shy. They would work in a motor that isn't worn out. Just an example of readily available non-resistor plugs. I'd use them, since they are sitting on my shelf, but I don't think they would get along with the Boyer ignition.

BTW, the R5671A-7 plugs I mentioned will mess with timing controlled EFI automotive installs. Been there. Really not EMI friendly at all.

I have to use resistor plugs in all the cars at my house, and use them on the Norton. Next time I start my Norton motor, it will have Autolite 5224 plugs in it just to see how they work.

kommando said:

Non resistor plugs will die out in the near future.

But

Click to expand...

I wouldn't count on that happening. You can still buy the old "massive" 18mm spark plugs for cars built in the 1st half of the last century. Non resistor plugs may not be stocked at the corner auto parts store, but they will be available.

Question I run a trispark, can I run without any resistors ,or if I need 1 am I better of with 1 in the plug or the cap ?

phippsy said:

Question I run a trispark, can I run without any resistors ,or if I need 1 am I better of with 1 in the plug or the cap ?

Click to expand...

From Trispark.


Recommended accessories with the Classic Twin

• NGK 5k suppressor caps (2 required). Spark plug cap (SPL-0030) or Small spark plug cap (SPL-0040)

That's where it gets murky again (for me)
If you elect to run a modern (fancy) spark plug it will most likely have a resistor (to reduce interference to other electronic parts ?)
Then what, non resistor caps.

Time Warp said:

From Trispark.


Recommended accessories with the Classic Twin

• NGK 5k suppressor caps (2 required). Spark plug cap (SPL-0030) or Small spark plug cap (SPL-0040)

That's where it gets murky again (for me)
If you elect to run a modern (fancy) spark plug it will most likely have a resistor (to reduce interference to other electronic parts ?)
Then what, non resistor caps.

Click to expand...

I was previously unaware that I was in the same boat, 5K plug caps as per Tri-Spark recommendation, but also with resistor Iridium plugs. When this was brought to my attention (it all ran fine) I did then fit non resistor caps...
Best described via seat dyno as: Yes, apparent improvement, but no 'increase' as such, just choke could be reduced earlier and engine reached it's 'comfort zone' way quicker... (SU fitted)

EstuaryBoy said:

(SU fitted)

Click to expand...

As per a previous post even NGK say "Since resistor type plugs actually “resist” some of the spark energy, non-resistor type plugs actually deliver a more powerful spark. It is for this reason that most racing plugs are non-resistor types."

Somewhere else I read copper is still the top performer and many of the fancy spark plugs are more for long term service in modern vehicles.

Why would NGK put a resistor in a spark plug when they themselves make a range of resistor spark plug caps, I can only presume many modern vehicles due to their abundance of electronic items need extra protection from ignition noise. (Or maybe it has something to do with spark plug mounted coil packs also)

(I had read somewhere else that the plug resistor was somewhat like putting your thumb over the end of a garden hose and it gave a longer and more intense spark)

Who knows but it seems prudent on an old vehicle (You would need some suppression with an electronic ignition) to not have both and some old things are getting caught up in what suits modern things.

Lets go Al.
Back in the 1990's I sent my 900 Ducati engine(bevel drive) to Vee Two Australia for the 80+ rwhp package (once I fit 41 FCR's)
I seem to remember the dyno sheet for it being run in read up to 9100 rpm (or might have been 9300)
It had come back with a new coil package to replace the OEM items and ran very well but there was a slight oddity and the squish band looked odd.
I removed the stock ballast resistors (iirc) and there was a noted improvement, a query reply from Vee Two said, did we forget to tell you those needed removal (they had not)
It never pays to take things for granted or become complacent or small things might be missed.