Spark plugs- ground strap”tech”?

[MadBill]

Maybe the sharp edges of the holes make it easier for a spark to jump to, compared to a smooth surface.

I seem to recall David Vizard some years ago advocating this mod for that reason.

[superpursuit]

I have always wondered why people pay so much attention to the spark plugs to start with - that's at a minimum the second gap that the electrical energy has to jump. The gap between the rotor and cap (conventional ignition) seems to me a place where some minor gains could be made. If you take a spare cap and do some cutting on it and then watch what the multiple spark boxes do plus watch what happens when you lead the rotor to cap tip timing, there's quite a bit going on. I am now setting up to have the leading edge of the rotor tip lined up with the leading edge of the cap. I believe this allows the rotor tip to put electrical energy across the cap tip for micro seconds longer and it certainly doesn't hurt anything. With the multiple spark boxes, the lower rpm range is much cleaner and I can stage the car more consistently. On the plugs I subscribe to the theory that electrical energy really prefers sharp edges and grind both center and ground electrodes to a nice point.

I set the vertical clearance of the distributer shaft to around .005”. I then cut a cap and measure the vertical distance from the tip of the rotor to the contact point of the cap. I then build up the tip of the rotor with silver solder and file that down to the clearance I want, around .020”. You’ll find the starting clearance is really wide. Maybe .075” or more? I also narrow the width of the rotor tip.

Jeff Lee are you using a locked out distributor?

To my way of thinking doing this with an advancing distributor would give you problems as the rotor advances.

[Kevin Johnson]

Maybe the sharp edges of the holes make it easier for a spark to jump to, compared to a smooth surface.

I seem to recall David Vizard some years ago advocating this mod for that reason.

Electric Fields on Uneven Surfaces
So far we have considered excess charges on a smooth, symmetrical conductor surface. What happens if a conductor has sharp corners or is pointed? Excess charges on a nonuniform conductor become concentrated at the sharpest points. Additionally, excess charge may move on or off the conductor at the sharpest points.

The lightning rods on our house have sharp points.

[Jeff Lee]

I have always wondered why people pay so much attention to the spark plugs to start with - that's at a minimum the second gap that the electrical energy has to jump. The gap between the rotor and cap (conventional ignition) seems to me a place where some minor gains could be made. If you take a spare cap and do some cutting on it and then watch what the multiple spark boxes do plus watch what happens when you lead the rotor to cap tip timing, there's quite a bit going on. I am now setting up to have the leading edge of the rotor tip lined up with the leading edge of the cap. I believe this allows the rotor tip to put electrical energy across the cap tip for micro seconds longer and it certainly doesn't hurt anything. With the multiple spark boxes, the lower rpm range is much cleaner and I can stage the car more consistently. On the plugs I subscribe to the theory that electrical energy really prefers sharp edges and grind both center and ground electrodes to a nice point.

I set the vertical clearance of the distributer shaft to around .005”. I then cut a cap and measure the vertical distance from the tip of the rotor to the contact point of the cap. I then build up the tip of the rotor with silver solder and file that down to the clearance I want, around .020”. You’ll find the starting clearance is really wide. Maybe .075” or more? I also narrow the width of the rotor tip.

Jeff Lee are you using a locked out distributor?

To my way of thinking doing this with an advancing distributor would give you problems as the rotor advances.

Yes...locked distributor advance.

[Caprimaniac]

Maybe the sharp edges of the holes make it easier for a spark to jump to, compared to a smooth surface.

I seem to recall David Vizard some years ago advocating this mod for that reason.

Giving higher probability of the plug fireing correctly. Maybe can go to a bigger gap than without the sharp edges, which can result in a better spark, more power?

[Dan Timberlake]

I have always wondered why people pay so much attention to the spark plugs to start with - that's at a minimum the second gap that the electrical energy has to jump. The gap between the rotor and cap (conventional ignition) seems to me a place where some minor gains could be made. ......

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I think life is pretty easy for the contacts inside a distributor cap. Maybe TOO easy, requiring relatively vast distances to keep the spark sparkin' where I intended.

Breakdown voltage (sparking) vs pressure in air vs gap/distance.

https://www.researchgate.net/profile/Du ... re-for.png

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The curves are most likely way different for air-fuel mixture, but my experiences with plug condition vs % throttle match those curves pretty good.
When the plugs were old and nicely coated with lead from Sunoco 260, I could put out the fire with just a tetch more throttle in My poor old Turbo Corvair.