Resistor vs Non Resister Spark plugs

Is there any real reason to use resistor plugs over non resister ones in power equiptment? In autos, the resistor plugs are supposed to reduce radio interference in your car, but why in power equiptment? Coil longevity, maybe? I would think the lower impedence in non resistor plugs would give a more beneficial, powerful spark. No particular issue here, but just curious for the reason.

 

My understanding its also for radio noise interference of other devices around you. Peoples TV, cell phones ect.

 

The resistor is to prevent electrical interference to sensitive electronics. They are required for any solid state coil to protect the primary side of the coil. (the part that contains all the low voltage electronics and sensing trigger)


It is very important to use the equivalent plug the manufacturer requires. Even more so with the electronic carbs/ injected stuff.

The benefit of a non resistor plug will give you more voltage available at the plug. Perfect match for the old early breaker points ignitions that where unable to produce high Kv secondary. The modern electronic ignitions are of high energy designs able to produce very high Kv at low rpms making starting easier. Also adjusting ignition timing for all loads and rpms are great but at a trade off of sensitivity to interference. That is where the resistor come to play by damping the interference.

 

We had better luck and less problems running resistor type on MSD ignition equipment, HEI and CD stuff.
Non resistor is good for basic magneto ignition with zero electronics.

 

Non-resisted offer a little more piston head room, if it's needed after machine work.

 

My little 1955 Fergie with Continental Z-134 strongly preferred non-resistor when it had points. Since I installed the Pertronix kit and coil either one works well. Champion plugs seem to work best so that's what I stick with. On this machine at least, ignition timing makes more difference than anything. Too much advance is counterproductive on this slow revving/low compression ratio engine, 10 degrees BTDC at 1500 RPM seems to be optimal. I do use resistor wires as they don't corrode inside the insulation like copper wires do.

 

The plug on the right is standard tip and the plug on the left is projected tip. Don't think resistor or non resistor makes that difference.

 

That's how Denso designates them.