I went to do compression testing on the car and removed the trailing plugs and they looked fine. I then removed the leading plugs to check their condition and notice the side electrode has been broken off and gone, on both leading plugs. The plugs has one season of track use and some street miles, probably 2k miles total. I asked my other two friends that also track rx8 and they said they had that happened before also and thought they were the only one. Is this a common thing or just a bad batch of NGK. this must have happened awhile ago because i've been trying figure out why the car was getting misfire since last year. but never thought to check the spark plugs since they were new. ive done compression test before but only pulled the trailing plugs and never checked the leading one.

Here's picture of the broken one.



Here's picture of an older plug from my old engine with 75k miles. The electrode is still attached.

 

As long as it didn't make its way into the engine you should be ok.

 

Never had it happen myself, but noticed that the one missing the electrode is cleaner, lolz

 

how could that even happen unless it can get pass the two oil seals on the side of the rotors.

 

the plug with the electrode still on it is from another engine. not from the engine that's in my car. i just posted the picture for comparison. both leading plugs from the engine in my car is missing electrode

 

Did the engine ever knock? I can see detonation hammering both electrodes off. The trailing plus sit in a little hole, so they're more protected.

 

It doesn't have to go by the oil seals to get in and whip around with the rotor.

 

Wait, both leading plugs are missing the electrode?

If they were purchased at the same time, they might have been a bad batch.

 

Did you install the plugs. If not it makes me wonder if the previous owner put them in like that.

 

yeah electrode missing on both leading plugs. i check with two other track buddies with rx8 and they said they have had same thing happened.

 

i install the new plugs when i installed the new engine last year.

 

didn't see any knock when i was logging on the dyno. unfortunately i don't have a way to log knock while on track. i'm running e85 and pretty much stock timing

 

Maybe you should post specifically which spark plug it is. If it’s the std 7 plug then you should consider at least a 9 plug for continuous wot track use. My engine builder would tell you to use at least a 10 plug for both.

 

i'm using standard 7 heat range. never really thought of using colder plug since im not running FI. but i guess things does get pretty hot when running constant WOT. where did you get colder plugs? i did a quick google search and was only able to fine RE8C-L on amazon. did not find any 9 or 10 range. the search on mazdamotorsport is useless.

also RE7C-L are $29 on motorsport but only $20 at advance auto. dafug

EDIT:
i found RE6C-L on motosport but no 8/9/10

 

So what exactly does a colder plug do? And is it worth it for very hard street driving. I kinda treat the street like a track most of the time. Shhhhh

 

colder plugs dissipate heat quicker and keeps the center electrode cooler, reducing chance of pre-ignition. but also not great for cold start in colder climate.

 

the Renesis-specific NGK R7440A- L / R7440B- T iridium racing plug is preferred but expensive, there are also aftermarket plugs like Denso etc and the NGK 13B R6725 / R7420 racing plug can also be used.

https://www.rx8club.com/series-i-maj...thread-253547/

I wondered if this also was playing into your cutout issue. If you have good spark and crank rpm they should light off fine. The only time I ever had slow starts was from a lowish battery in cold weather. I never had a single Renesis flood, not even in 20 deg F weather with E fuel.

not really interested in addressing street car stuff, my comments are specifically for TJ.
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so it looks like the cheapest place is direct from NGK. 9 for leading and 11 for trailing. is it important to have two heat range step between leading and trailing like oem? or run 9-L and 10-T

https://www.ngk.com/product.aspx?zpid=10138

https://www.ngk.com/product.aspx?zpid=10140

 

Well if your concerned about cost you could run 9L racing and 9T stock or if you don’t mind the cost then 10/10 all racing.

I don’t see any need to stagger or run 11T

 

ordered four R7420-10 from autozone. with 20% discount code and free shipping. win

 

I saw you had asked about dwell a while back. I did end up dropping those numbers down some over concern for quality variance on the D585 coil and its tendency to have sporadic auto-discharge at high dwell. That’s my main reason for switching to the IGN-1A. Which I always knew was the coil to be using.

 

yeah i saw your response to that thread. i have removed the LS setup when one of the coils died while i was at the track few months ago. luckily i brought the oem setup in my spare parts box and was able to continue racing. i think i'll just stick with oem coils for now and just replace often and keep spares around. also didn't want to mess around guessing the dwell settings.

 

So only difference between R7420 and R7440 is gap. 0.7mm vs 1.2mm (which is rx-8 spec). what kind of impact does that have in track conditions?

 

you want the smaller gap

the trailing plugs for the Renesis/R7440 are a different reach length though (19mm), but the 21mm reach on the R7420 can be used. I would recommend the 10.5 per your cross-posted thread in the racing area.
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