Spark plugs. Why is it so hard?

Electrical and Ignition

  1. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    Oh so now since you've lost the electrical conductivity argument, you're switching to thermal conductivity. Nice work. That's kinda like changing global warming to climate change, ain't it?
     
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    • Bewy

      Bewy Well-Known Member

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      Let's here YOUR electrical conductivity argument. So far it has been a big, fat ZERO.
      Post up your theory, with supporting evidence, of how the electrical conductivity of 1/2-3/4" of copper makes a difference to spark plug operation.
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      I already have, sir.
       
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      • 92b

        92b FABO Gold Member FABO Gold Member

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        Thanks to RRR and Bewey I have learned more about sparkplugs and how they operate. Information provided has been very helpful. The name calling, profanity, and chest thumping not so much.
         
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        • Phreakish

          Phreakish Well-Known Member

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          Resistance doesn't matter that much. We put 4k ohm resistors into spark plugs to kill RFI noise (and wires too, most have a pretty high resistance!).
          *edit*
          Turns out, the resistance also helps kill capacitive after-fire (a second spark after the initial spark, caused by the capacitance of the leads and spark plug body). Capacitive after-fire won't help an engine run better, but can wear electrodes faster. The resistance of plug wires and spark plugs also helps limit current through the ignition system to prevent burning out coils and distributors. Low-resistance wires are often marketed with hype about their low resistance, but in reality they simply add a highly conductive material that makes them 'measure' low, but in reality are not a significant part of the electrical path for the spark and therefore don't actually improve anything. But a lighter wallet does go faster, right?
          *end of edit*
          Low resistance won't do anything either since spark plugs and wires work on inductance not conductance. I'm not an EE, but I do know for a fact that resistance doesn't matter much if at all (until it's so high as to create an open circuit). High voltages overcome resistance quite easily, however it does it.

          I'm trying to find the charts and graphs which show the change in breakdown voltage for spark plugs based on standard vs iridium, vs platinum. I know I've had several motorcycles which require iridium plugs because the charging system was too weak to keep copper plugs clean!

          Here's at least one source, with quotes from Autolite's director of engineering, stating that the fine wire iridium plugs can reduce coil requirements by as much as 20% - which means by switching to iridium, one could open the spark gap considerably with a stock coil.

          Also notable:
          "Fine-wire iridium plugs can improve the combustion process even if there is a high level of exhaust gas dilution—built-in EGR—as with engines with long-duration camshafts with a greater amount of overlap."
           
          Last edited: Jul 30, 2021
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Thanks! Now that makes sense....and without all the down under condescension. lol
           
        • 448Scamp

          448Scamp Running Free

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          Yes sir, I read that. And the only thing I read that was performance oriented was that a fine wire plug takes less voltage to ionize the gap. I don’t think anyone here would argue that. I don’t think anyone here would argue that a precious metal center electrode will last longer than a copper electrode plug. I do know that several ignition engineers I’ve spoken with all have a different opinion of how the ionization of the gap occurs. And that’s an issue because depending on which understanding you follow will directly impact the choice of spark plug. Also in the conversation must be the fact that current OE ignition systems are miles ahead of what most here on a forum like this use. These OE ignitions will fire less than optimal chamber conditions (either rich or lean of stoich and even at that it’s only stoich to about 5% rich for best chamber conditions near the plug) much better than say the Chrysler ignition or the many knockoffs of that concept or even the much ballyhooed HEI. In the case of running these less efficient and powerful ignition systems, a precious metal center electrode can cause an undetectable misfire, which in turn causes an O2 sensor to read rich when the engine isn’t really rich at all. In the end when all the chatter has fallen away, it remains if the ignition is up to snuff then the only benefit to a precious metal center wire is its working life span.
           
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          • 448Scamp

            448Scamp Running Free

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            Which is exactly why these plugs were developed. Because the ignition system was so weak you get misfires. The benefit of longer life was a byproduct of that plug development. The correct answer is get the best ignition system you can find. And use a precious metal electrode plug if you don’t want to change your plugs very often and you don’t mind a lighter wallet. And at that none of this addresses the issue of a copper electrode plug causing ionization to occur easier than other electrode types. Even the engineers can’t agree on that.
             
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            • Phreakish

              Phreakish Well-Known Member

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              Note entirely. Both platinum and iridium deal with heat better. As a result, they can be run 'hotter' without as much concern for preignition. That means the plugs stay cleaner, and they also stay sharper longer - which means better spark for longer, or better spark with a 'hotter' ignition system longer than a copper plug would last. It also means that they deal with non-ideal conditions better since the plugs are better able to fire with increased EGR, sub-optimal AFR, and will put up with abuse for much longer than copper.

              My take is this: tune with copper, fine-tune with platinum or iridium after and then enjoy the car. There's no reason to run a tuned-up engine with anything but platinum or iridium, especially with a souped up ignition (MSD, etc). IMO: copper doesn't last, doesn't stay in-tune (no one replaces plugs before fiddling with the carb), and aren't well suited to anything but stock applications. As soon as you have more spark, more cam, more abuse, copper just stops making sense.
               
            • Phreakish

              Phreakish Well-Known Member

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              Yep - copper is a relic of a bygone era.

              Even if copper ionizes the same (it doesn't, due to inherent design constraints which limit minimum electrode size to bigger than it needs to be), it won't last long enough to matter since the electrode will round off rapidly with anything but a stock or low powered ignition.
               
            • 448Scamp

              448Scamp Running Free

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              I wouldn’t argue any of that. My thinking is plugs are cheap. I still am not sold that other than the fact that the center electrode is a fine wire that the fine wire plug does any better at firing than a copper electrode. Even in the link Bewy posted the author never really developed any thoughts that I haven’t heard before, and that is the life span of these plugs is better. I’m still in the camp that if you can get to your plugs the copper electrode is better. I think that some wear of the center and ground electrodes makes firing the gap much easier and more consistent up to the point they increase the gap so far the ignition can’t keep up. I think this is a case of the technology adapted by the OEM’s doesn’t always translate to what people on a forum like this do. I also appreciate your comments on plug wires. I’ve spent a lot of money on plug wires with very low resistance and they were not half as good as some plug wires that had more resistance. It’s marketing hype for sure.
               
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              • Phreakish

                Phreakish Well-Known Member

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                If you like changing plugs, coppers can work. Or if things get changed frequently, then coppers make sense.

                There's no drawbacks (other than cost) to the exotic plugs. They last longer, self-clean better, resist fouling and perform better under boost, under higher pressures, at high rpms, and do so without having to resort to higher powered coils (which just burn out coppers faster). When higher powered coils are already in-use, the exotics don't wear as fast and keep performing at their best for much longer than a copper will - because they don't need to tax themselves to death in order to function well.

                It's also possible to use exotics to get even more out any ignition system by allowing the plug to see as much current as possible in order to run a larger gap and a hotter spark for more reliable or faster ignition. Changing plugs and coils won't make a well running car go faster (unless the ignition is already junk) but a well designed ignition is necessary to make big-cammed, high-compression, high-revving engines run well.

                With all that said: OPs question was about what to use for his combo. He's running EFI with a hyper-spark in aluminum TF heads. I'm running similar (FiTech with computer timing, MSD blaster 2 coil, TF heads on a SBM) and what worked for me is what I described above: I ran the Autolite copper plugs to get my tune (ignition and fuel) dialed in closely with a focus on timing. Then switched to Autolite XP3924 iridiums and opened my gaps from .035 to .045. Since then, things have remained stable and worked flawlessly. Plugs look good when visually inspected and show less soot and absolutely no wear. The copper plugs had rounded electrode edges (soft, not spherical) with only about 500 miles on them.
                If the plugs are an issue in the tune they'll show it. Pull and inspect them often. If they're fouling, burning up, or failing with little use then a change may be warranted. If it won't run with the recommended plugs it's likely because the ignition system is not a good match. That's unlikely to be an issue unless adapting some other OEM ignition system onto the engine though.

                Just my $.02 - worth the price paid.
                 
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                • Bewy

                  Bewy Well-Known Member

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                  Just to be clear, the fine wire plugs also use a copper capsule buried in the centre electrode. The copper is used to increase the plug's heat range, due to copper's excellent heat conductivity.
                   
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                  • toolmanmike

                    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                    Which may or may not be the right heat range. A guy in another thread is tearing his hair out with a rich running condition and I bet it's related to too cold of a heat range.
                     
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                    • 448Scamp

                      448Scamp Running Free

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                      As an update I almost had to call 911 last night. I decided to look into some platinum plugs and nearly stroked out. I found plugs as much as 14 bucks. EACH. At that cost it had better be an instant 20 pounds of torque everywhere. I’m still on the fence about it. If they last 5 times longer they are cheaper than conventional plugs. The upfront cost is a real gut punch. I think I need to do some more research.
                       
                    • 68383GTS

                      68383GTS Well-Known Member

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                      Mother Mopar used Champions. I have used Champions in all my slant 6's,Small blocks and big blocks without ever any issues. 20+ Mopars in 35 years.
                       
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                      • Bewy

                        Bewy Well-Known Member

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                        Scamp,
                        14 bucks ea? I'll swap ya! $32 ea here for NGK Iridiums last time I checked. I tried to buy them from Summit where they were cheap, but NGK had a deal with Summit to not ship outside the country. Did I hear somebody mention 'free trade''.....
                         
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