Knows some stuff...
My Thoughts About Spark Plug Issues
A spark is a spark, not brand or design has anything to do with it.... For the most part.
A cheap ol' copper plug will be just as good as platinum or possibly iridium. I will explain and expand on this later. But, to clarify, it has nothing (directly) to do with the material used, rather the size/shape of the electrodes. The reason iridium is used is due to its great strength and high heat tolerance. Because it has such strength, it can have such a small tip and not break off under the high stress of combustion. So the small tip is what makes it work so well, while the material is what allows the tip to be so small without breaking.
Copper electrodes start square and have a 'tip' on the four corners and work almost as well as the Iridium. The problem with copper is it is so weak so micro particles break off and the corners get rounded and the gap increases. Platinum is harder than copper, which makes them last longer that copper. The corners won't wear as fast, and the gap won't increase so that is why they could be seen as slightly better. The actual spark occurring from them is no different than the copper and the performance is the same. Iridium is about 8 times harder than platinum and melts well over 2000°C (2466 °C/4471 °F)
Electricity arcs better the smaller the point, and iridium allows for a very small point. But iridium is more expensive than copper or platinum. The wider the gap, the longer and hotter it will burn and the fatter the spark. The smaller the gap, the shorter, smaller and less hot the spark.
The ideal thing to do is gap the plug as far as you can without blowout. If your spark gap is too wide, the combustion 'blows' out the spark, which is much more prevalent in F/I engines. So gapping a plug out of the engine and setting it to a point just before it no longer arcs is a bad idea. You will have blowout as soon as the first combustion happens and your engine will run poorly. If you use factory specs, you will be fine, though if you want to find the optimal gap, it will take some tuning/adjusting.
Basically just keep increasing your gap .0025” until you get misfire (at your highest boost level), then close it back by .005". They have aftermarket type devices that boost your spark voltage and have shown to keep a spark between .1” gap at 30 psi! Though something like that really isn't necessary for 99% of our applications and can add wear and tear to electronic parts and would require some beefing up in that area. But the wider the gap, the longer and hotter the spark will burn propagating the flame kernel and burning more fuel, more completely. You can only burn so efficiently, so if you are already at that point, a spark voltage booster or a wide gap won't do anything for you.
Having a spark gap too close will kill your performance. It won't be blown out, so some cheaper tuners who don't use a spark booster just close the gap (old school 'trick' apparently), but chances are they are killing their performance potential. They are turning up the boost and it is blowing out and misfiring, so they close the gap, they lose the misfire, and think they are all good form the higher boost. Though they probably are making more power from the added boost, they are making less than their full potential of power from the smaller gap. The smaller gap the less time the spark is available to burn and it isn't as hot so your fire kernel is potentially smaller and not burning as thoroughly robbing you of power and fuel efficiency.
The HMA spec for spark plugs is .0394”-.0433”. I checked mine and it was ~.028! I couldn't believe how narrow that is. This is why I think our Genesis Coupe tips are so black. Not from a rich mixture (as rumored), but from small gaps not burning it fully. As I was getting knock on my stock car so I know it wasn't rich (running 13:1 AFR at times when wide open throttle), but I still had black tips.
I have heard of 16%hp being gained from a proper gap. This is probably where certain companies boast about their horsepower gains from their plugs. They probably test a less than proper gap vs. a proper gapped plug (though they still stay in specs to be ‘fair’ and to be able to say “we used factory spec gaps”), but we just saw how gap spec can vary from 394 ten thousandths of an inch to 433 ten thousandths. It isn’t some crazy material or ‘special research’ or some voodoo magic that gets their spark plug gains, it is a proper gap. If you gap was so small that you would gain more than 16hp, you would be having misfires from the spark so small it couldn’t ignite the fuel at all. So if you go to a proper gap, you could gain 16%hp I could see, but anymore than that can't really be gained as your car wouldn't be running to measure the low efficiency dyno. 16% brings a stock car from 210hp to 243hp. But it is also possible (and very likely) they tested with a proper gap and your car is running as low as 176hp. Though we are talking the largest change you will most likely see.
Even though the gap on my car was very low, I don’t expect to see more than a ~5-7% gain as .028 is close compared to stock, it could be worse. There have been dyno’s testing wheel horsepower that have ranged from 175whp to 195whp and some of that is drive-train loss, but some of that could also be the cars having a crank horsepower of 190hp from the small gap you might have. Again to clarify it isn't really 'gained' as much as it is not being as lost. Basically putting back in the efficiency that you lost from an improper gap, and I am not guaranteeing you any gains, but the potential is there.
You do need to be more careful when gapping iridium and need to do it correctly. You must take extreme caution to NOT TOUCH THE CENTER ELECTRODE, THE POINT COMING OFF THE GROUND STRAP or THE PORCELAIN when making adjustments. This is probably why Hyundai doesn’t touch them, and companies that make iridium pre-gapped plugs say it is best not to touch them. Though as I have explained all different cars have different gap requirements based on boost, compression and many other factors and car manufacturers must make a car that ranges from enthusiast, to soccer moms, to granny drivers. These sites do say they adjusting them is not needed, but if you must, then it is imperative that you do it properly.
Use needle nose pliers and grab the grounding strap from the back along the sides and squeeze to get a grip, then bend it up or down to adjust as necessary and use a spark plug gapping tool to check your gap.
This is just my observations/thoughts. I take no responsibility for anything that happens to your car if you decide to change your gap and ruin your plugs or your engine runs poorly. But mine is now at .040”. I had some blowout at 20psi running .043”. I think with stock boost, I would have run .045” to test it out, but at my higher psi (running close to 20psi), I feel the top end, but lower than max will be a good first test to see if I get misfires or not. I might get a better gauge and open the gap if I run with no blowout or misfires for a while, but it is hard to get a gap that close to specs using the needle nose pliers. Also, It might not make a difference, but the fuel trims could be learned... so since it is so easy, you might as well pull your battery and reset your trims. And before pulling your spark plugs it is a good idea to disconnect the negative terminal from the battery anyway.
Heat range also has nothing to do with spark, it has to do with how long your electrode or your engine will 'last'. If your plug is too cold, it will dry foul (unless you have an oil leak and it wet fouls which can't really be cleaned) and you will get misfires unless you clean it more often, but it is safer for your engine. If it is too hot, the carbon deposits on the electrode will burn off so you won't need to clean it..... but you may get pre-ignition and blow up your engine instead. Basically the electrode is so hot, it ignites the fuel pre-maturely before the spark fires while your piston is travelling up, and this is very bad for your engine. Erring to the side of cold is a wise decision when you start to modify your car. Some say rule of thumb is 1 degree per 100hp gain. Since the spark plugs on this car take a whole 2 minutes to get to, it is very easy to clean and I would err cold rather than hot. If you do decide to use copper, erring to the cold side is even better as copper's don't really last that long and require service to re-gap you can go ahead and clean them while they are out, or buy new ones since they are so cheap.
Coppers should be checked every 1k miles. Also, where does that copper go when it 'explodes' off? In your engine, which most likely your oil and filter take care of it, I would rather not have bits of copper floating around. On WRX's and such where the plugs take an hour or so to get to, though you wouldn’t want to clean/service as often iridium and a proper heat range sounds more ideal. I have heard of iridium lasting 100k miles if not for a bad tune. Hot plugs is just more ceramic (insulator) so the electrode stays hot, the less ceramic, the metal dissipates from the plug to the engine block and the electrode stays cooler.
Cleaning your dry fouled copper plugs is as simple as a wire brush and some elbow grease. I don't feel comfortable doing that on iridium (though it might be fine), you can take advantage of its high heat tolerance (over 2000°c). Take a blow torch to it ~1300°-1700°C to burn off the carbon deposits.... the same thing your engine would be doing if you had hot plugs.
The more I think about it, the more this makes sense. People in the Genesis Coupe community are getting terrible MPG (compared to what Hyundai says). A smaller gap, not allowing the fuel to fully burn would do this. People also say their oil smells like fuel, also would make complete sense as if the fuel is not being burned completely, it is getting into your oil. And as I said those complaining about blacked exhaust tips, would also makes sense if fuel is not getting burned the whole way and you are getting carbon deposits on your exhaust tips much like you would on your spark plugs if the heat wasn’t there to burn it off.
Or if you do have (and need) colder plugs, if you don't beat the crap out of your car, you will still need to clean them more often from fouling. If you need the colder plugs for harder driving, that means harder driving is necessary to heat your plugs up and clean them every now and then. So now you have an excuse to beat the crap out of your car and have some fun. If your plugs are too cold, you might not ever reach that range no matter how hard you drive and that is why you don't want to go too too cold, though I think erring on the cold side is better than the hot side.