Hello Paul - when you were testing spark plugs, did you ever test the type that fired to the rim - did not have the little arm for gapping - I used these type of plugs back in the early 70’s and found they were great - don’t think they are around for cars anymore, but think they are still used in outboard motors.
Surface discharge plugs: used them in all my 2-stroke engines.
No power advantage, but they tended to not get “whiskers” from the burnt oil.
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jury out on platinum and iridium for older cars that do not have all electronic computer controlled igniton systems with coil on plugs or high electric voltage output systems. Iridium plugs are designed for modern cars, they also do not have the normal heat ranges, and tend to run as a colder plug…this is because modern computer controlled ignition systems manage the engine ignition. The electrode in the iridium plug is tiny…and in older carburettor, non computer controlled cars can foul. Iridium requires less voltage, but on the other hand is not as good as a conductor as copper. Platinum conducts a little better than iridium but not as good as copper. What iridium and platinum do, is hand extreme heat better…good in computer controlled turbo engines. Like really extreme heat that is never generated in the xk engine…(if it was…a piston would burn out quickly). There is no advantage to iridium in the XK engine, and possibly not as good as copper. Can you install platinum or iridium? sure…and will probably run ok, but copper core plugs as we have listed them will work as good or better.
Nick
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The heat generated by combustion is a fraction of the temperature of the plasma at the spark kernel, which can reach 4000K. Iridium points are less prone to erosion at high temperatures. True in all motors. It’s the same reason that tungsten is used for contact points in the distributor, relays and fuel pump. The iridium point can indeed foul in an overly rich non-ECU engine, this can somewhat be offset by using a higher heat range plug. The point remains that iridium plugs will be less prone to pitting and erosion wear.
The electrical properties of the metals are pretty much irrelevant. Copper, platinum, even plated steel all perform equally well.
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Michael…agreed. Nick
What about gap? Thoughts on when to have more or less than the 0.025 rec? My two seem to burn really rich- damn “auto adjust” sz’s. Changing to the manual jets seemed too much for me to do myself n the common carb guy rec to send to was way overbooked.
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Back in the 1970s and 80s, I used mainly Champion in my Mk2. I tried Bosch when they first appeared - they were really poor. I tried Golden Lodge and never had to replace them!
Nowadays, I use NGK in all my cars. When/if I get the Mk2 running again, I suppose I’ll have to change the 40-year old plugs?
I, too, had used Champion plugs for a very long time, as my father had, back into the 1930s. In the early 80s, I begin to have a disturbingly high number of Champions fail, mostly as high-pressure misfires. I switched to NGK, and I’ve never looked back.
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Iridium electrode IS tiny- crap- guess I messed up. I put gap at 0.030.
What little I know: David Vizard, one of the real wizards for modifying British motors writing on resistance sparkplugs, recommending their use for more than noise suppression
" When the spark jumps the gap at the plug, the resistance of the plug, due to the arc being formed diminishes to nothing. … Under these conditions, the current goes up, the voltage drops and the spark becomes self extinguishing.
With a little resistance in the system, the spark can be increased in both duration and temperature."
The trick is to make sure you don’t have more than 5000 ohms. Many people wind up with a resistor plug, resistor wires, a cap with a 5000 ohm center electrode, and a resistor wire from the cap to the coil, all of which just kills it. I recommend to people with ignition issues to test the resistance from the contact inside the cap to the central electrode in the spark plug, and also from the bushing in the cap to the end of the coil wire.
Iridium plugs. My understanding is that these were developed for use in lost spark systems, such as the Ford EDIS system that some of us use in their cars. In these systems the secondary wiring in the coil is grounded though the complementary spark plug, and this requires a spark plug that will effectively fire when the current flows from the side electrode to the center electrode, the opposite of what is usual and which occurs in the plug that’s being fired. Iridium plugs are expensive and not necessary in most cars.
Just to kind of put this on top of the conversation: there is no magic spark plug!
Any decent spark plug, properly gapped, will provide exactly the same amount of performance as any other spark plug.
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THAT’S a wall keeper!
As mentioned earlier in this thread…
“Iridium points are less prone to erosion at high temperatures. True in all motors.”.
That, and the fact that fuels are much cleaner, means that iridium plugs don’t need changing as frequently as conventional plugs use to.
That’s why, despite the high cost, I use them in my E-Type’s engine. Less frequent changing of plugs = fewer changes in stress on the plug threads in the head = less chance of a thread going soft and stripping.
I’d agree with this. Going back to my story way back in this thread, the sparkplug engineers at Autolite (who really knew their stuff) told me this: “the principal reason for increased life in sparkplugs was simply no-lead gasoline. Any sparkplug we manufacture will easily last 100,000 miles. But don’t tell anyone because more that half our sales and 70% of our profit comes from aftermarket sales. We like customers who change sparkplugs once a year!”
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The NGK BP5ES, 6ES, 7ES…now not manufactured…replaced all, by Resistance plugs…were 1,000ohm, now 5,000. Well…when does it matter…it matters …a little…but matters a LOT…if one makes the mistake of getting modern spark plug wire set, made for cars with hi energy systems…these wires will be in the 20,000 to 40,000 ohm resistance ranges…per foot of wire. You want very low resistance wires…ZERO to 1,000 at most. Run these modern hi resistance…and your plugs won’t like it, no matter which you choose, NGK still my choice.
Nick
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If Kettering, copper or steel core wires are fine.
If Pertronix, you MUST use resistor wires.
Pertronix now sells 7mm resistor wires that fit older looming, it hides well. 50 ohms@foot.
I keep 100’ spools in the shop.
Use crimp ends, as the Champion screw in plug caps will not make a good connection.
Use a 3 ohm flamethrower coil, paint it silver, slap on a lucas coil sticker, and it is pretty stealthy.
https://www.amazon.com/NGK-BP5ES-Spark-Plug-4-Pack/dp/B004SKLPZM
Couldn’t find BP6ES NOR 7ES on Amazon, though
Bought a forever supply of BP6ES for my E and Spite from a UK supplier about a year ago. They are out there. Normal pricing at about $2.xx ea, freight by courier in a few days a $10 per package. Couldn’t buy more than 25 at a time or it went to another freight method which took the freight way up. So did 2 purchases.
Here’s a link to the NGK spark plug boots. Hard phenolic resin body with wire and plug rubber boots. These can be had with 0 resistance, 1k, 5k, and 10K depending on the style I think. There’s an NGK table in the link. High quality cap that looks similar to the old Champion caps and gives you the resistance or not. Nice with Cu wires and non-resister plugs. The 1K caps knock out interference to amps, did for mine. Shop around, I see them from $3 to $12 each.