What size Plug gap do you run ?

The only problem using a wider gap at the plug is that it really stresses out the coil insulation. I know it doesn't seem like a few thousandths should matter, but the voltage spike on the primary can go from 300 or 400 volts to 600 or 1000 volts. This means the igniter's output driver has to deal with a much larger voltage to insulate against. This means the coil's insulation also has to deal with that. The secondary side will be around a hundred times higher than the primary side. Eventually, the spark energy will try to find an easier path to take.

10 years ago when I started building igniters (not the HEI ones), I used old coils for testing. When I bench tested them in open air using a 3/8" gap (in open air the pressure is much lower so you use a much wider gap to simulate the cylinder pressure), the coils lasted indefinitely. If I increased the gap to about 3/4", they would last a couple hours then you'd hear a little ticking noise in the coil and the spark would get real weak, then eventually stop. After that I could barely get a 1/4" gap out of them. Granted, these were 30 year old coils, but they were in decent condition.

The compression ratio makes a difference. The higher the cylinder pressure is before ignition, the higher the voltage stress is on the ignition. On one of my gpz's (which has higher than 10:1, maybe 11:1) I can't go much higher than about .035" on the gap before the wires start or coils start to bleed off.

I'm not saying to not run a larger gap, but if it runs fine or basically the same with a normal gap, then I'd say use the normal gap to get more life out of the coils and igniter. This could just mean the coils last 20 years instead of 40 years, so maybe it doesn't matter.

I talked to Dyna about that and they told me directly that it is no problem. I was told that in some applications people run as much as .100"-.120" gap on the plugs with those coils. I was worried about that also, so I called them to ask just for that reason.

Well, as I said, maybe it's just a longevity issue, or maybe newer coils are just better, but I doubt they did much stress testing on old igniters, or maybe they did, but I would assume they tested with their own ignitions. I guess if the old Kaw igniter pops, the HEI's are cheap enough.

Cool! Otto is setting me up with the good stuff.
I've had these 3ohm Dyna coils sitting on my shelf for over a year. Now I can use 'em!

Gotta rewrite some ZZ Top now.

New coils, new wires, when I twist back I'm gonna fly-like-fire...:laugh:

otakar wrote:

I talked to Dyna about that and they told me directly that it is no problem. I was told that in some applications people run as much as .100"-.120" gap on the plugs with those coils. I was worried about that also, so I called them to ask just for that reason.

But they are in the business of selling coils.:laugh:

The Kettering ignition is a flyback design. I used to wind switching transformers and there is always a tradeoff. More (and better) high voltage insulation between winding layers costs money and increases size. But, transformers do fail over time. Heat is a major stressor, but the high voltage creates the E field that works on the insulating material and eventually punches through. Dyna coils may have a good operating life at wide plug gaps, but it definitely increases stress for the reasons already listed (higher voltage induced).

I had forgotten about the induced back EMF on the primary working over the solid state switch, but that's real too.

bountyhunter wrote:

I had forgotten about the induced back EMF on the primary working over the solid state switch, but that's real too.

Yeah, I knew it was there, but still managed to smoke a oscope probe somehow. It was up to about 600v before it went. Not sure what happened. Probably the voltage divider shorted.

Well he is ONLY going to run .045" gap which is a standard non radical gap. So, there's no worries. I'll experiment with the .060" gap on my bike.

On my B2 GPz 1100 I installed my 2.2 dyna coils, 8mm taylor wires. I broke one of my iridium tips, better that happened in my gapper vs the engine so I bought BR8ES (IIRC) instead. Gapped to '0.525'.

Bike revs quicker and cleaner the top end is noticeably more aggressive. Since I am at 4200ft I'm not sure if that plays a role in whats best for my gapping.

I have run as much as .80 with no problems and had good response. That is a whole 2mm gap. The problem comes because the coils start to run much hotter and you get feedback into the ignition. I found that .60 is the best of both worlds. I do not run Iridioum or any of the new metal plugs because they do nothing for our bikes. The ACCEL/ND U plugs are still the best and last the longest.

+1 on the ND U plugs. Ed

Hollywoodmx wrote: ...BR8ES....

The "R" means its a resistor type spark plug, with resistance being built into the plug itself.

Where resistance is desired in the secondary loop, it may be introduced in either of three places:
• An "R" spark plug;
• A resistor incorporated into the cap that clips onto the spark plug;
• Suppression type spark plug wires.

Should NOT combine these, as a single form of resistance is sufficient.
And using more than one introduces too much resistance.

It would be a royal screw-up to use R plugs with suppression wires and resistor caps.

On older vehicles where electrical interference is not an issue, no resistance is needed, and B8ES (non-R) plugs with solid copper core wires and non-resistor caps may be fitted.

On newer vehicles with electronic advance ignitions or other sensitive electronic equipment, resistance may be added to the secondary loop by using one, and only one, of the mentioned methods.

Have successfully long enjoyed using on Z1 and KZ900: NGKB8ES (non-R), and Dyna solid copper core plug wires with built in non-resistor caps. But the ignition overpowers most local audio sources.

Good Fortune!

Sorry I did buy the B8ES's, not the R's although the iridiums were r's.