spark plugs for track use
 

As I was driving back from from track day yesterday I realized that I have put 10k of mostly track miles on my S2 since I got it 5 years ago. Car had 28K miles when I got it at which time I changed spark plugs with OEM ones along with driveline fluids (transmission and diff filled with redline oils) which are probably also due for a change - what is preferred track diff fluid these days (redline came out with new 75W-110 GL-5 Gear Oil)?

Car still seems to be running strong but it does run out of steam past 8000 rpm so I am wondering are the OEM plugs ripe for a change after 10k miles of hard track use? If so would I benefit from running colder plugs (over from what OEM heat ranges are) and if so which ones do you guys recommend for a car that is mainly driven to/on/from the track and occasionally on the weekend here and there?

I was also thinking about changing the coils and plug wires at the same time.

Aside from the OEM plugs and the Denso ones(which are a bit colder), I haven't seen any other options unless you count the FD RX-7 plugs that some people fit in.

If the car is mostly stock, stick with stock. You can pull your spark plugs and examine them if you want, but I would think track use actually prolongs their life, since deposits are cleaned off. My own mixed track/street use hasn't necessitated changing plugs more often.
Colder plugs have downsides when you're not running at full tilt, so consider that too.

If the car is running out of steam, check your cat and try to narrow down the cause.

10.5 at least

there are a number of options depending on how much you’re willing to pay.
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Its what I did in my car, but it's an endurance race car and spends 1.5hrs per stint between 6500 and 8500. I ran 2 steps colder on the leading plug and 1 step colder on the trailing plug. When I did my initial plug swap I found the electrodes were MIA. 😳

It's got a fresh engine with stock plugs until I get it broken in.

Cat is fine, it is sitting in my garage :-). Car has 38K miles and is still on original coils/wires so that is first order of business. I will pull the plugs to see how they look. Track use should keep plugs cleaner but should also wear them out faster due to lots of time spent near redline - I would guess center electrode will wear out faster than with street use.

Team looks like I have two $ensible options as far as using colder racing plugs, which one would you recommend:

1. NGK R7420s all around - heat range: 10 or 10.5, gap: 0.7mm, center electrode: 0.6mm , reach: 21mm, ground electrode: slant ~$25
2. NGK R6725s all around - heat range: 10 or 10.5, gap: 0.7mm, center electrode: 1.0mm , reach: 21.5mm, ground electrode: flat ~$30

third is not really an option - ridiculously overpriced
3. NGK R7440s all around - heat range: 10 or 10.5, gap: 1.2mm, center electrode: 0.6mm , reach: 21mm, ground electrode: slant ~$65 :eek:

Both have smaller gap then stock leading plug (1.1mm) which should be good at high rpm and will make life easier on coils?

I wonder if center electrode thickness difference plays any role on performance and longevity?

How about ground electrode angle slant vs flat?

hm, this missing electrode seems like recurring theme....
did you run R7420s or R6725s?

the recurring theme is don’t hammer the engine WOT for long periods on hot heat range plugs. Loosing the electrode wire is the least of the damage being caused.

I resisted listening to one of the most experienced and knowledgeable rotary race engine builders for many years before finally realizing I was a complete idiot and he knew more than I could possibly ever hope to know on the subject. With that reorientation of removing my head from down under to where I could see and hear the truth of his words, all these things make perfect sense to me now.

the difference between them is platinum vs iridium and the cost of that, for what you’re doing the cheaper platinum option is fine.

edit: well they used to be cheaper. I found them both online for $30./each. So go R7420 iridium then. You might check on MMS, but for the longest time I was buying them for less doing some serious searching online. Not sure why the Renesis-specific iridium racing version costs so much more. Probably less volume sales maybe.

But you should preferably use 11 or 11.5 on the T side
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here is R7420 slanted ground electrode

https://cimg1.ibsrv.net/gimg/www.rx8...171d4acdc6.png

and here is R6725s flat one, looks more sturdy but also more recessed inside plug

https://cimg3.ibsrv.net/gimg/www.rx8...0f0a533fb4.png

Proving once again that experience matters :p:

Yes Brettus, I’ve tried to share it with you may times, but you still refuse to hear just as I previously did. You can also find comfort in my posting many times that nobody has made more dumb mistakes in their life than me. Which I had to edit this post too for not thinking clearly the first time through.

Getting back on topic; which btw said topic isn’t new on the forum:

Same ground strap on both, same thickness, same Platinum material with angle difference and center electrode material difference; Iridium vs. Platinum.


https://cimg6.ibsrv.net/gimg/www.rx8...96b467f6a.jpeg


https://cimg2.ibsrv.net/gimg/www.rx8...a3eecbe53f.jpg


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So I called local part stores and no one can't even order R7420s in 10 or 10.5 heat range. Only Autozone had 2 R7420 in 9 heat range which got me thinking if I could run 2 of those as leading and leave stock training plugs which are also 9 heat range for this weekend track day?

They do have different gaps, stock is 1.2mm and R7420 are 0.7mm will that cause problem?

or should I swap leading plugs with 2 spare OEM trailing plugs and run 4 stock trailing plugs (RE9BT) for this weekend until I get my hands on 4 R7420s?

For reference, Denso IRT0131 is equivalent of 10 heat range in NGK scale(every company has their own scale). The Denso IRL0127 is equivalent of 9 heat range in NGK scale.

They can be ordered on Rockauto easily. Just putting this out there.

perhaps worrying too much on the wrong details

I sent a pm that needs a time-urgent response

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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.

Just to share, this is what I ran in my 6 port 13b race car, should be fine in an rx8 also. Handled high egt wot situation with zero issues in hot climates.

br8eix spark plugs - trailing
re7c+l spark plugs - leading

Someone will ask why a colder trailing plug. I was doing some negative split tuning. It worked.

all those cracks and erosion around the spark plug holes were an issue even if not recognized as one

So I’m glad I stumbled upon this also. I also have a new to me Low mileage series 2. I’ve been to two track days and run it very hard. I swapped brand new plugs, wires and coils from bhr when I got it and before the track.
So based on the above chart shared looks like I need.
R7440A-L. In a ten heat range and a
R7440B-t. In the 11 range. Is this correct?

Yes, or R7420 in colder, but understand those cold heat range plugs are intended for high engine load conditions. Low engine load conditions (street use) are likely to result in early fouling.

It wasn’t unusual at all for pre-Renesis race teams to use warm plugs to start and pre-warm an engine, then swap in the cold plugs for the race. This was more for engines with high port timing overlap that our more susceptible to flooding during cold start conditions. That’s not as likely on a decent condition Renesis engine that has no overlap porting to contend with. If Renesis engine compression is low that might crop up as a potential issue.
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Thank you sir, this will mainly be used on the track at very high rpm. Even when I do drive it on the street it never makes it very long before it’s sitting very high in the rpm. Already on my 3rd set of tires since buying it in July.

i got R7420-10 plugs from Autozone last year based on Team's recommendation. even used 20% discount codes on them.

https://www.autozone.com/miscellaneo...lug/198704_0_0

https://cimg5.ibsrv.net/gimg/www.rx8...b00ba7a7d9.jpg

I'm wondering if there is any better option for an rx8 that is driven hundreds of street miles to-and-from events and then competes in both sprint hillclimbs and longer time attack sessions and then drives hundreds of miles home...

i'm used OEM plugs from day 1, but i have had electrodes become weaknened and break off when i pulled the plug. but i also street drive and drive in cold (down to around 32F) weather, so i'm not sure how colder plugs will treat me. almost sounds like i should have two sets of plugs... one for commuting to events and for autocross/hillclimb, and another set for time attack and track use.

rx8 plugs are easy enough to get to, so wouldn't be a bad idea to swap out plugs for track day. only thing is wear and tare on the housing plug thread.

Here’s what my OEM heat range spark plugs look like after 10K miles of mostly hard track use. Got deposits?


https://cimg1.ibsrv.net/gimg/www.rx8...4b31a9581.jpeg

https://cimg9.ibsrv.net/gimg/www.rx8...bf6e4c26c0.png
https://cimg2.ibsrv.net/gimg/www.rx8...bb09836cd0.png