best for spark transfer; dull or sharp edges?

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Rapid Robert

Rapid Robert

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I had always thought that sharp edges on rotor/plugs had a lower required voltage to jump a gap than smooth ones but the other day I read something about dull edges are better (might have been an MSD article) but I may have misread it. thank you for your time. RR
 
Sharp edges. When the edges round off it’s time to replace the plugs. Plus you can learn a lot from how the plug is wearing.
 
Cats aren't sharp, that's why they can build up a pretty fierce charge on a dry winter day when you pet them. If cats came with sharp edges they would discharge more easily and you wouldn't get a shock that you could notice. Balloons are the same, but they won't claw and bite you if you try to stick them to the wall with static electricity. Hey! I was 7 years old.

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Someone explain a Nippondenso U-groove then. I dont think they did all that R&D on a dud design? Modern plugs are very small tipped. I think its because the platinum/iridium/ruthium is so much better at not corroding/burning off it can be made very small (plus its expensive) while the Champion pencil lead tip had to be made fatter to last longer. Interesting topic, need some links to some white papers on the subject.
 
Screenshot_20220117-205617_Chrome.jpg
David vizard in his Holley carb book
Talks about rounding the ground electrode on spark plugs to unshroud the center electrode for better flame travel.
Also keeps the plug cooler.
I did it recently on a set of plugs in my 340
One thing I've noticed is no more pinging
On acceleration that it used to do occasionally.
But he also says they don't last very long.
 
If they propogate easier off an edge the (ND) U-groove marketing may be right? Here is an opinion:
"..Sharp points ionize the surrounding air more quickly and it will conduct sooner and more reliably, with a more concentrated spark
that is supposedly hotter. It's why platinum plug electrodes are so
thin. And it's why lightning rods are pointed.
The (NGK) V-groove (and ND U-groove) leaves more sharp edges to do the job than a
square-cut elecrode."
 
The benefit of a U groove plug is that it lasts longer. The spark jumps across the gap where the resistance is least [ usually smallest gap ]. Every time the spark jumps, a minute amount of the metal is chipped off the electrode until the gap gets bigger; the spark then finds another spot to jump from with less resistance. U groove electrodes just provide more area, so last longer.

Plat, Irid plugs require less firing firing voltage because of the small volume of the electrode. The electrode could be steel, but would soon melt. That is why high melting point [ expensive ] electrodes such as Plat, Irid etc are used.

The smart hot rodder would see the benefit of reduced firing voltage as a means of increasing plug gap without getting misfires because the ign system is maxxed out. There is no such thing as too big a plug gap [ except for mechanical contact ].
 
pishta said:
If they propogate easier off an edge the (ND) U-groove marketing may be right? Here is an opinion:
"..Sharp points ionize the surrounding air more quickly and it will conduct sooner and more reliably, with a more concentrated spark
that is supposedly hotter. It's why platinum plug electrodes are so
thin. And it's why lightning rods are pointed.
The (NGK) V-groove (and ND U-groove) leaves more sharp edges to do the job than a
square-cut elecrode."
Click to expand...


The platinum plugs are that thin because they can take the heat. They take more ignition to fire. Their only benefit is longevity.
 
Plat plugs [ & Iridium ] take less voltage to fire. That is one of their benefits & why they are used: less emissions. They have less misfires, all else being equal, because of their reduced firing voltage requirements. This means that as the electrodes erode & the gap grows, they will still keep firing, reducing emissions that would come from misfiring plugs.
 
Bewy said:
Plat plugs [ & Iridium ] take less voltage to fire. That is one of their benefits & why they are used: less emissions. They have less misfires, all else being equal, because of their reduced firing voltage requirements. This means that as the electrodes erode & the gap grows, they will still keep firing, reducing emissions that would come from misfiring plugs.
Click to expand...
Can you post your information source on that? I've always read that copper conducts better. As a better conductor, it would seem that it would take less voltage to fire, right? The only benefit I'm aware of with platinum, iridium or any other "exotic" metal is that they simply last longer.
 
Mopar69gts said:
View attachment 1715854813 David vizard in his Holley carb book
Talks about rounding the ground electrode on spark plugs to unshroud the center electrode for better flame travel.
Also keeps the plug cooler.
I did it recently on a set of plugs in my 340
One thing I've noticed is no more pinging
On acceleration that it used to do occasionally.
But he also says they don't last very long.
Click to expand...
I’ve done that to a set of Autolite race plugs like he mentions, even though the end is ground back and rounded there is still a 90° edge. Kind or a tedious job grinding and trying not to hit the center electrode as you grind but a neat mod nonetheless
 
RustyRatRod said:
Can you post your information source on that? I've always read that copper conducts better. As a better conductor, it would seem that it would take less voltage to fire, right? The only benefit I'm aware of with platinum, iridium or any other "exotic" metal is that they simply last longer.
Click to expand...
I’ve run Denso iridium plugs, some NGK iridium on a few motorcycles, most noticeable differences were on a 79 Triumph Bonneville 750. It started (kickstart) easier, had a more consistent/steady idle, was able to try lowering the idle speed below the ideal (just to see) and it had crisper throttle response when cracking the throttle. Slightly more responsive. That was all I saw, easier starting, strong idle and snappier throttle response. Couldn’t discern anything else when riding it, accelerating etc.
From my research at the time it was due to the thin center electrode design, not due to a metal. That it was a iridium only allowed longer life using such a small diameter electrode.
 
12many said:
I’ve done that to a set of Autolite race plugs like he mentions, even though the end is ground back and rounded there is still a 90° edge. Kind or a tedious job grinding and trying not to hit the center electrode as you grind but a neat mod nonetheless
Click to expand...
Yep that's what I'm running too
Autolite 3924R
It was tedious and took some time
I used the end flap off the spark plug box
To put in between the center and ground electrodes to keep from damaging it with the file.
They still look great after about 1500 miles
I was running the standard Autolite 3924's
Before switching to the Race plug.
I think they are a click cooler plug by design also.
So far So good!
 
RustyRatRod said:
Can you post your information source on that? I've always read that copper conducts better. As a better conductor, it would seem that it would take less voltage to fire, right? The only benefit I'm aware of with platinum, iridium or any other "exotic" metal is that they simply last longer.
Click to expand...


This is correct. All the plugs with other than copper electrodes are there for one reason and one reason only and that’s extended mileage. Nothing else. The OE’s had to go to them because most people don’t change their plugs often enough (much like oil changes) and the computers get pissed off when the plugs start to fail and cause misfires.

Plus these new cars (most of them anyway) are a real ***** to change plugs.

They are not performance plugs. Not by a long shot.
 
12many said:
I’ve done that to a set of Autolite race plugs like he mentions, even though the end is ground back and rounded there is still a 90° edge. Kind or a tedious job grinding and trying not to hit the center electrode as you grind but a neat mod nonetheless
Click to expand...


You should be able to buy Autolite’s with a cutback ground wire. Everyone else makes one.
 
12many said:
These are what I used on motorcycles. One of the thinnest center electrodes, able to be made thin using iridium in order to last. Any benefits observed was due to that 0.4mm pinpoint thin center electrode, not the metal

View attachment 1715854844

IRIDIUM POWER - Features | Products | SPARK PLUG | Automotive Service Parts and Accessories | DENSO Global Website
Click to expand...


Glad you posted this. If you have a weak ignition system, any fine wire plug can show an improvement. If it does, you are better off upgrading the ignition system than using a fine wire plug.
 
Rat Bastid said:
You should be able to buy Autolite’s with a cutback ground wire. Everyone else makes one.
Click to expand...
Yes. Vizard mentions the race Autolites that are already cut back, but he cuts them even further back as shown in one of his books. I did that and indexed them just because, not that I could ever tell the effects.
 
Rat Bastid said:
Glad you posted this. If you have a weak ignition system, any fine wire plug can show an improvement. If it does, you are better off upgrading the ignition system than using a fine wire plug.
Click to expand...
Two motorcycles I used them on one had Lucas electrical parts (known as the Prince Of Darkness) and the other is an India made points ignition single cylinder Royal Enfield. Those two did show improvements as I mentioned, the others were modern multi cylinder bikes and I didn’t notice anything honestly
 
I don't know if this has been said already because I only read the first three posts but the shape of the electrode is going to partially determine the shape/size of the spark...yes hotter spark/higher energy spark influences as well..duh.
So while the electrode rounds off the closest part is what's going to spark and that's going to be a smaller/narrower body of energy...but does it matter and how are you measuring it?
If we are seriously looking for hp from plugs...you may as well piss up the splitfire rope.. just dont catch your pants on fire saying you gained power. Jk

Best of luck.
 
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Along with sharp edges, the side electrode prep, from Vizards “How To Build Horsepower” book:

1D3EF9B7-BF58-465A-A99F-8F5DA36544F0.jpeg
058475C4-9E9B-4102-A737-CCEE1CB01579.jpeg
 
Here's a link to spark plug materials if it were possible Rhodium or Osmium would be the choice being so much more wear resistant than the other metals in the platinum group
Guide to Spark Plug Materials

Here is a pic from NGK website Iridium versus $20 per plug Ruthenium
NGK68716-graphics-for-web-DURABILITY-768x443.jpg
 
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RRR,
[ Post 12 ]. Talk about the electrode material can be misleading. The copper core is NEVER exposed to the flame. It is a cartridge buried inside the centre electrode, usually a composite of steel & nickel.
The info I posted can be found on the net from releases by NGK, but I also have some technical releases from NGK, which is where the above came from, #T01-7.
Too long to type out all of it, here is a snippet: 'With fine wire electrodes, the electric field is concentrated across a smaller surface area with sparking able to occur at a lower voltage.....' A graph included shows a reduction from 24kv firing voltage down to 20kv going from the standard 'thick' electrode to a 0.6mm electrode, for a 0.060" plug gap.
Also: 'Reducing the centre electrode diam of a spark plug reduces what is commonly referred to as the quenching effect [ ie, heat energy loss from the hot flame kernel to cooler electrodes as the flame attempts to expand & combust the mixture]'.

The reduction of the resistance of the short length of copper [ vs steel ] in the centre electrode would be immaterial in spark delivery because there are much higher resistances already in the circuit [ coil sec res, leads, rotor gap etc ].
 
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