Suggested plug gap with Dyna S

1976 kz 900. I've been using 36 thou for the past couple of years and have had no apparent problems. However, just cooked my 1/4 coil and subsequently the 1/4 Dyna pick-up so, just wondering other's thoughts on plug gaps? 36 thou good? Too wide?

BH

The gap is dependent on the voltage out of your coils. I run .050 (1.25mm) on my stock Kawasaki ignition with Dyna 2.2ohm coils. so far 10,000Mi. and no problem

Otakar, thanks for the input. I'm running a Dyna S with 3 ohm coils.

Not knowing as much as I should about the relationship between ohms, volts, amps etc, are you able to run a 50 thou gap because your running 2.2 ohm coils? Is a 2.2 ohm coil capable of putting out a higher voltage than a 3 ohm coil, assuming the same voltage input?

There's obviously a corrallation between the voltage output of the coils and the gap used but is there some rule of thumb? Say upto 30,000v, don't use a gap larger than 30 thou? Can 1000v jump 1 thou? Is there anything linear about this relationship between volts and gap?

Thanks.

BH

Jeff from z1 mentioned in the recent past that the only time he's seen dyna's cook is when the motors get real hot down there. Might want to call dyna and discuss this with them. I talked with them once and found them very polite.

BARNEYHYPHEN wrote:

Otakar, thanks for the input. I'm running a Dyna S with 3 ohm coils.



There's obviously a corrallation between the voltage output of the coils and the gap used but is there some rule of thumb? Say upto 30,000v, don't use a gap larger than 30 thou? Can 1000v jump 1 thou? Is there anything linear about this relationship between volts and gap?

Thanks.

BH

There is a relationship but it's not simple. I depends on altitude, humidity and pressure as I recall. The spark also jumps easier depending on what ions are in the gas.

Back when I built HV power supplies, the rule of thumb was to use 0.1" air gap per thousand volts to PREVENT a spark jump at sea level. At higher altitudes, the sparks jump a lot more easily.

I think a typical plug with an .032" gap will probably fire in the 5 - 10 kV neighborhood, that's a guess.

FYI: I am not convinced widening the gap and forcing the coil's secondary winding to a higher voltage improves performance, but it does increase voltage stress on the coil winding. I think any decent spark is going to work. If you are standing in a room filled with gasoline vapor, it probably won't matter whether you strike a match or ignite a road flare.... same result.

Spark plug gap has been an age old performance question. It has mainly been divided into two lines of thinking. Some go for a short fat spark and some go for a long narrow spark.

With an electronic ignition, the coils have a longer charging time, therefore more spark and can use either gap. Most people when using super high compression, go for the short fat spark. There is less chance of the spark being blown out with a shorter distance to travel.

I have used wide and narrow plug gaps in the Z motor. Now days I try to find some middle ground (.030"-.040"), I have found no real differance. I have went as high as .055" with the Dyna and Martex. I perfer .030"-.032" with a Mag.

Perhaps the results would be better noticed if you used the whole nine yards, side gaping, plug indexing, two plugs per cylinder, various plug gaps, diff heat ranges,
etc.

Every motor is different, you just have to play with it. I guess for me, it's just peice of mind.

Thanks all the input. Think I'll probably go with 34 thou.

BH