well, the topic may not be too catchy as i hope its useful to all. id like to keep useful topics here as TTT just explained. i hope we can get some people to chime in on this.
i was reading a few differnt articles when i came across a spark plug comparisson chart. contenders were the NICKEL/COPPER duo, the platinum plug, and the IRIDIUM heavyweight. well i find that the only benefit that the platinum plug has over the older, cheaper nickel/copper plugs is that they last longer. the N/C plug will however produce more energy as they have lower resistances. Iriduim on the other hand has a lower resistance(at least half of the copper) while being able to last over 4 times that of platinum. toyota is ditching the platinum plug for the iridium in the IS300 and also the VVTi equipped cars such as the celica. i will however look for charts to support my statements. if any of you want to chime in on this. my question is why do we pay high bucks for the platinums if we change them before 10K miles. im sure the copper will benefit us more.
kris

 

that is all very interteasting nice find, so which ones are the best for a heavily moded rx-7? I don't know much about spark plugs, but I do know that they cost a arm and a leg. I've got the platinum ones, should I have gotten any different ones?

Regards, Matt

 

its little like synthetic vs regular oil. do you spend more and change it a little less, or change it more and spend less?

mike

 

im guessing that for a heavily modified RX7 the iridiums would be the way to go. we have one guy on the forum that has tested many. all i remember is that he had a banner with the words "SILVER BULLET" in it. check his site out. im just looking for what would be the best depending on how you drive the machine.
kris

 

yes, i guess it could be compated to the oil thing. however, we change them out sooner then more platinums should be changed. if anyone uses copper plugs please let me know how they hold up and at what interval you change them at. changing the platinums at uner 10K miles seems like a lot. changing them at close to the same, for cheaper and more of a benefit in power would be better. copper heads, let me know.
kris
this all started when i read a post on the honda-tech forum. they had no evidence to back it, so this is why i am doing it. i may just have to pull out the ohm meter later and see what i get

 

copper DOES have lower resistance and should give out a better spark compared to platinum and thus doesn't last as long. The reason why we change out platinums at under 10K or even under 5K miles is b/c the sometimes and other stuff.

I use coppers all 9's trailing and leading with no adverse affect on my car.

Danny

 

where are you guys getting the copper ones from?

for some reason, i can only find the platnium ones.

also, how much are these costing you guys?

 

I think most of the BIG GUYS are using copper race plugs. Regular copper are way cheaper then the platinums. They are the same part number without the "p" on the end.

BUR9EQ

 

Iridium plugs are way too ******* expensive. I haven't heard of any good results in a rotary application, either.

 

where are you guys getting copper plugs from. i can get platinum plugs for like 6 bucks ea. and coppers for 4. they don't seem that cheap to me. is there a place out there that i can get em for like 2 bucks each?

 

My understanding is different that some of what I read here.

First of all, the difference in material is not their resistance to the flow of electricity, but rather their durability in the nasty high temperature combustion environment. And because high cost materials survive better, they can be made smaller and still function well. This takes us to point number two.

Larger diameter electrodes also require higher voltages before the spark will jump. This becomes more significant as compression (or in our case, boost) goes up, and the required voltages can become quite high. If this requirement exceeds the available voltage from the existing OEM ignition, we get miss-fire and loss of power. This is in part why many heavily boosted 7's MUST use ultra-high output ignition systems.

Therefore, with more durable materials the electrodes are smaller in diameter and in the same environment will require somewhat lower voltages to produce reliable spark.

 

are the copper electrodes larger than the platinums?

 

Try this:
http://www.silverbulletrx7.com/

 

I heard the same thing too.

 

Iridium Spark Plugs are standard factory equipment on the RX-8. There's a rotary application for you. And yes, they are ultra expensive, like $40 or more each

 

how does a larger diameter electrode require more voltage to spark?

 

It's all about charge density. I don't remember the exact formula for arching to occur, but I know that the denominator is some function of A. So increase A, and you need more charge to get it to arch, or spark.

 

I get my NGK 9's from the dealer. $7.50 a pop and they pay for themselves by providing better gas mileage for 3,000 miles.

 

well the highest charge densities are found at the sharpest points. in this case its the circular edge between the flat end and the side of the electrode. i cant see the relatively small difference in electrode diameters making a big difference in this.

 

so we should be able to use this in hi-powered FDs, right? ie single turbo

 

As somebody above stated my site has info on all of this along with the Rx-8 plugs, which I will test when I get a chance. As for platinum vs non there really is no reason for platinum in our cars.

 

double post

 

No, the highest charge densities are found on the seperate pieces of metal in the plug with the smallest surface area, i.e. the electrode. Make the electrode smaller, and you've made the charge density quite a bit higher.

Like I said, I don't remember the equation for charge density, but I know that Area would be in the denominator. It very well could be A^2 or A^3, meaning that the charger density would increase with the square or cube of the area. In which case small change in area would equate to a relatively large jump in charge density.

 

Question: with the RX7 rich starting mixture and occasional starting problems (and rotor oil) at start, is there any spark plug wisdom on plug temperatures to use to maintain good starting performance and avoid fouling?
Q2: Is there a procedure to burn off carbon during commute cruising? Like drop to low gears and engage both turbos for a minute or some such cleverness?
Note 1: Mazda owners manual says not to use synthetic oil in the Wankel, no prohibitions against silver electrodes1

 

Those spark plug facts are nothing new. The only advantage of the platinums is longevity. IF you have the dealer change them then it's beneficial because that's less times you for labor. If a dealer includes this in their free maintenance then it's cheaper for them.

Using oil as an example as a few of you did allready. With synthetic and free dealer oil changes they recomend them every 15k mi. If you pay for it yourself then it's every 3k mi. Actually it used to be 5k mi but the the quicky lubes advertised every 3k to make more money.

The higher the boost, the colder the plug. It's not a benefit it's an expensive necessity.