Spark plug choices

JAX71224 said:
OK So mine still has points but uses the Dyna coils. Why would it need resistor ANYTHING in the secondary side?
Click to expand...
Whatever happens on the secondary is reflected on the primary, meaning that if you have a high performance coils, you may experience shortened points life without some resistance in the plugs or caps, but the original OEM coils are so anemic that resistance doesn't do anything except reduce the temperature of the spark, which does open another discussion. It's not the spark that ignites the mixture, it's the relatively high temperature of the spark that does the trick!
 
Yes, run resistor something on the secondary. Another benefit, the current limiting of the resistor increases the time duration of the spark.
 
So I need some resistance on that side, eh? Would a 1k plug boot be enough? Hey just thought that I have used nonresistor caps and plugs for wifey's 65 mustang 289 with a MSD Blaster coil. No ill effects found yet but that car get very few miles per year, just to occasional cruise-ins or car shows..... Yes AM radio is noisy but we don't usually listen to that anyway! The NGK plug boots keep wires off the headers and survive the heat better that any automotive ones tried!
 
Last edited:
2Many,
Well, the dual output coil is a single coil that has to jump two spark plug gaps because the gaps are effectively in series. If the gap is .030, then that amounts to a .060 effective gap to "jump". Once the gaps are breached, the effective resistance of the gaps decreases greatly, so the heat generated is higher and its the heat that ignites the mixture, not the pretty blue spark itself.
That's why all dual output coils are called "high performance". Not only do they have to produce a Voltage high enough to jump two spark plug gaps in series, but the positive Voltage spark plug requires as much as 40% more Voltage for the same efficiency as the negative wire.
 
The other part of that is that one cylinder of a waste-spark system will always be on the exhaust stroke. The high temperature and probably partially ionized exhaust significantly lower the voltage requirement and resistance at the plug gap. Most if the spark power goes where it's needed: the compression stroke. Higher resistance there means more of the spark energy is consumed in jumping the gap.
 
Adding something to this thread.
I picked up a tuning kit for the XS650 at the Yamaha store last week.
In the box were new points (did not say China on them), condenser and 2 plugs
The plugs were Nippondenso W22EP-U

I have not used these plugs as of today.
 
Those might be a pretty good plug. I never tried one but I may look into them seeing that the NGK BP7ES is getting harder to find.
 

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