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spark plugs for track use

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Old 05-01-2021, 06:21 PM
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there’s no shortage of people to hang out with in the won’t take heed to sound advice club

how they look is meaningless in a rotary; whether they fire or not under high load is all that matters

you probably have them gapped too wide anyway since nobody thought to bring that up, especially if they’re the RX8 rotary specific plug ...

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Old 05-02-2021, 07:31 AM
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Originally Posted by Snox801
Steve from versa tune is gonna be dyno tuning my s2 in a few weeks to gather some more info.
Hopefully he will be able to collect good data. Car is all stock except cat is removed from stock mid pipe for track sessions.
just waiting for him to say the dyno is open.
Hey did you ever do the dyno tuning with Steve? Results?
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Old 05-02-2021, 12:23 PM
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I tapped them and will be going colder once I am able to get the plugs. Especially for the longer tracks with more wide open straights. I tapped them myself after using a search on here cause I didn’t want to be that guy.
I know rotary’s can’t be read like normal plugs hence why I said for what’s its worth which isn’t much.
Steve has not got back ahold of me. He said they had some dyno issues and that got the shop backed up a bit. So just waiting to hear from him.
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Old 05-10-2021, 04:46 PM
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Good discussion. One other thing you should look at with plugs is coils & leads... with ~20 track days per year I figured I needed plugs once per year and coils+leads every two years.

Or get aftermarket coils, but then you need to do more research on what really works.

Based on this thread I should probably be running colder plugs though. I've been running NGK RE7C-L + RE9B-T and can't say I've noticed an issue with running hot on track aside from the set that came out of a failed motor that I probably left in too long.

For tuning, MazdaEdit worked on my series 2.
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Old 05-10-2021, 07:43 PM
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I have the bhr coils in mine. And plan on doing them probably every other year. Unless Charles thinks differently.
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Old 05-10-2021, 08:07 PM
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You don't need to replace BHR coils at the same rate as OEM coils. Test them. Mine are on their 10th year & 100,000km.
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Old 05-10-2021, 10:03 PM
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if you’re talking about the previous D585 type you might want to load test them, there were failures of individual coils for sure

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Old 05-10-2021, 11:31 PM
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Originally Posted by Loki
You don't need to replace BHR coils at the same rate as OEM coils. Test them. Mine are on their 10th year & 100,000km.
that’s good to know thank you.
I just installed them last summer they have been working great.
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Old 06-01-2021, 11:10 PM
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another one to consider for those losing grounding straps, available in -8/-9/-10/-11 heat range and only 19mm deep

I think Motorsports only carries -11,

-10 is the recommended minimum, -11 is preferred

https://www.ngk.com/ngk-4586-r6601-11-racing-plug

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Last edited by TeamRX8; 06-01-2021 at 11:13 PM.
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Old 06-03-2021, 10:09 AM
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the grounding strap welding on the R7420-10 looks a lot stronger than the rx8 oem plugs.
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Old 01-15-2022, 10:47 AM
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Originally Posted by Nadrealista
PM sent.

I red this on racing beat web page regarding the spark plug gap recommended for high RPM/track use. Looks like they gap down their plugs to .015" ? Can NGK 7420/6725 even be gaped?

Spark Plug Gap/Torque

Virtually all modern stock engines use relatively large plug gaps for good idle and emission purposes. However, as power and RPM increases, large plug gaps require more and more ignition energy to fire reliably. There is no exact relationship, but expect to reduce plug gap as power and RPM increase. In all high output race engines we use a gap of .015". If the gap erodes to .020" or more, power loss usually occurs.

When using our Racing Beat recommended spark plugs in street applications we find a gap of .020" to be a reasonable compromise. When using the following plugs for performance applications: BR7EIX, BR8EIX, BR9EIX, and BR10EIX - we recommend a gap of .015". We recommend that a drop of engine oil be applied to the threads, and using our Thin Wall Spark Plug Socket.

I also checked RockAuto and they have above mentioned Denso iridium plugs in stock in 9 leading and 10 trailing heat range - these are equivalents of NGK R7440-9 and 10. They also have NGK R7420-10 and R6725-10.5 in stock as well. Out of those I can only get R7420-10 by Friday, rest next week.
i can't find the R7420-10 on rockauto. how did you locate?

edit, it shows up as " NGK 5501"?
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Old 01-15-2022, 10:55 AM
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Originally Posted by TeamRX8
another one to consider for those losing grounding straps, available in -8/-9/-10/-11 heat range and only 19mm deep

I think Motorsports only carries -11,

-10 is the recommended minimum, -11 is preferred

https://www.ngk.com/ngk-4586-r6601-11-racing-plug

.
these are interesting because there's no grounding strap to loose?

but it appears that the 8 and 9 heat ranges are NLA...
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Old 01-15-2022, 01:05 PM
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you don’t really want to run under -10 any way, so moot point

think I may have some -9s though if that’s what you want, collected them at significantly reduced pricing over the years.
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Old 01-15-2022, 01:31 PM
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also, for the RX8 specific race plug the -9 is only available in the Leading plug, here is all the info you need with the Part - Stock number correlations



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Old 01-16-2022, 10:43 AM
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Originally Posted by TeamRX8
you don’t really want to run under -10 any way, so moot point

think I may have some -9s though if that’s what you want, collected them at significantly reduced pricing over the years.
.
my blue car is now my daily driver (my only car, actually). yesterday i did 2 hours of 70mph highways cruise and 3 cold starts between 25-35F. march 5 i am doing time attack at summit main with a 2200ft straightaway. this is my dilemma. in the spring it will see a combination of autocross, 2 hour highway cruises. sustained high rpm at track, and occasional short trips for groceries.

would any of those plugs work for this mix?

on my white rx8, i used oem plugs for 4 years with this sort of mix. not saying i didn't do any damage, but i didn't foul and it ran pretty good overall.
Last edited by hufflepuff; 01-19-2022 at 11:45 AM.
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Old 01-16-2022, 11:38 AM
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just change out the plug at the event? it's not that big of a deal to change out leading plugs. and just run oem trailing plugs all the time. do you keep your track pads on for daily driving also?
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Old 01-16-2022, 06:51 PM
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the rotor housing plug holes likely had a lot of cracks and the apex seals were jumping and flying off of the overheated spark plug mountain pretty good.
Last edited by TeamRX8; 01-17-2022 at 11:02 AM.
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Old 01-17-2022, 01:22 PM
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Originally Posted by TeamRX8
the rotor housing plug holes likely had a lot of cracks and the apex seals were jumping and flying off of the overheated spark plug mountain pretty good.
Team,

Can you describe how the spark plug heat range contributes to this in a rotary? Is it detonation, or the fact that the plugs are recessed, and the overheated tips cause local hot spotting in the aluminum? I understand what a too hot plug does in a piston engine, but I can't understand how these characteristics, which I know exist in race/high power use, can be attributed to plug choice in the rotary. Since you have been racing this engine longer than anyone here that I know of, I know you have researched this thoroughly. Please let me know.
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Old 01-18-2022, 10:11 AM
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Originally Posted by TeamRX8
the rotor housing plug holes likely had a lot of cracks and the apex seals were jumping and flying off of the overheated spark plug mountain pretty good.
i plan to tear down my white car engine in the near future and will take detailed notes and pictures to share with the community.
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Old 01-19-2022, 09:03 AM
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Originally Posted by hufflepuff
i plan to tear down my white car engine in the near future and will take detailed notes and pictures to share with the community.
Let me know when you are going to do this, want to give you a hand and learn how to tear/put together rotary engine :-)
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Old 01-20-2022, 08:18 AM
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Originally Posted by Nadrealista
Let me know when you are going to do this, want to give you a hand and learn how to tear/put together rotary engine :-)
will do, although i can only promise to be successful at tear-down. assembly... is another story ;-)
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Old 02-09-2022, 09:41 AM
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Originally Posted by hufflepuff
will do, although i can only promise to be successful at tear-down. assembly... is another story ;-)
I am sure we can handle it, I mean what could go wrong
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Old 02-11-2022, 08:11 PM
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welp, i bit the bullet and ordered the NGK R6601-10, part number 4017. NGK.com actually had them for <$21/ea and free shipping. i am hoping the -10 heat range will work well for my dramatically variable usage. will report back...
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Old 02-13-2022, 02:52 PM
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you might need to keep an eye on them for wear, especially if high power coils are used, since the center electrode is only nickel material on those particular plugs.
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Old 02-14-2022, 07:26 AM
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Originally Posted by TeamRX8
you might need to keep an eye on them for wear, especially if high power coils are used, since the center electrode is only nickel material on those particular plugs.
.
for sure, i will keep ad eye on them and report back on how they're working with my driving profile.

i suspect i will probably foul them before the nickel electrode wears out, but we will see!
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