Use of RX-8 Iridium plugs in FD
 

Hey guys...been tackling some issues with ignition cutoff on my single turbo, and I asked Rick at Rotary Performance about it, and it turns out that he's been using the NGK RX-8 iridium plugs (all 7 range) and has had very positive results with it. Of course, the plugs are about $20 bucks a pop, but still...apparently they last for quite some time without fouling and are great at resisting detonation.

His original e-mail:
"I have had similar issues with my car over the years. I have had to replace the leading coil, but even after that, when running higher boost (14-15 psi) the car would crap out at higher rpm. New stock plugs would work for a few days, then it would start running poorly again. I finally fixed the problem. I am using RX8 spark plugs - the #7 heat range in both the leading and trailing spots. I gapped the plugs to 20 thousands of an inch. Now the car runs sweet, and has been for over 6 months. I pulled the plugs out once to check them and they look good. I was a it concerned initially about using the #7s in all spots, but after talking to Skip at KD Rotary he assured me that I would have no problem with detonation or rapid electrode erosion. They have done may dyno pulls with the hotter plugs with no ill effects. Apparently the iridium RX8 plug conducts heat very well out of the tip."

and in a follow-up:
"By the way, I had tried the hks iridium plugs in the #10 heat range. Even with the small gap, they would foul out after a month or so of street driving. When I pulled them out they were dark and had deposits on them. The RX8 plugs just seem to work well at least on the street."

Anybody else have any experience with this? I trust Rick quite a bit, and he had rebuilt my motor a few months ago, so I'm sure he wouldn't recommend anything he wasn't sure would work...

PM Skywarpr , he runs rx8 plugs and it fixed his slight ignition problems and such, and no problems yet.

only 20 bucks a pop now? I remember when the rx8 first came out and the plugs were about 60 a pop, and you could only get them threw the dealer

I believe www.sparkplugs.com sells them for $20 bucks each. It looks like they're not scheduled to be changed in the RX-7 until after a few years!

I've tried NGK's BR7EIX iridium plugs (Photos here), although they aren't rotary specific. After 3K miles, the electrode tip is still like new, while the electrode on the factory-spec NGK copper plugs is noticeably rounded off after 3K miles.

Have you got any closeup photos of these RX-8 plugs? From what I hear, they're not the flat-face design like the RX-7 plugs. I wonder if there's much of a difference between RX-8 plugs and NGK's -IX series of plugs.

-s-

I have also heard of good results with the Rx-8 plugs. I have some details on my site. Denso is coming out with a version as well. I haven't had time to test them yet though. As for runnings 7s I don't know... They do make 8s though so I'd at least buy that heat range to be safe.

It looks like sparkplugs.com has the denso plugs for the RX-8, but they are $35 bucks each! I can't tell what the heat ranges are given the part numbers since I'm not sure how Denso categorizes...

For $20, ill stay with the Stock plugs, until they get a little cheaper to afford. Guys the stock plugs can't be all that bad.

I just use ngk 9's all around. I may consider this iridium plug theory along with a twin power once I raise boost. I'll talk to Dylan.(I hope I spelled his name right... I always get it wrong!)

Jeremy

or they are Doubling the hp output of the car and it is one of many upgrades/compromises that must be made. do some reading man that statement could offend alot of people on here

They sure did put them in for a reason, same reason they put catalytic converters and an air pump on the car for.

RX-8's run 7's & 9's, not all 7's. They are not $20ea either. The only difference is the reach is longer on the leading plugs and for the RX-7 they are the same length. When NGK eventually makes some iridiums then you'll be able to get them for $20ea. The first brand out with the plug is allways higher priced.

http://www.sparkplugs.com/results_ap...1&AAIA=1416844
http://www.sparkplugs.com/results_ap...1&AAIA=1192508

Ummm...goracer, the link you posted seems to take you to the site I was originally quoting, and they do list the NGK plugs for $20 bucks each. If you click on the "More Info" button, they state that the NGK plugs have an iridium center electrode.

superior force, can you post a photo of the RX-8 plugs please?

Thanks,
-s-

The RE7AL has 21mm reach, while our stock ones are 3/4" = 19.05mm.
The 2809 with 9 heat range has 19mm reach, which should match our stock ones fine.

This is a very interesting thread to monitor
I will need more info before I move to RX8 plugs but it seems very promissing indeed

Wow, you sound like you know a lot. We should all start listening to you.

Btw - People dont run colder plugs due to detonation. They run colder plugs due to preignition.

I wouldnt put much stock into what KD does for high performance cars. Seems like the majority of what they do with them is blow them up.

Stephen

Yea, thats better. But I was really hoping for more technical information. Since all the people running 10's and 11's are doing so because they are paranoid about detonation and there is no real need for it, I was hoping you would shine some of your wisdom on the subject. Please....tell us why everyone should be running 7's all the way around.

I'm curious to know what knowledge and wisdom you have gained that is so much more vast than everyone running 10's and 11's. Do you even know why people bump up to a colder plug???

Stephen

The majority of people I see running 10's and 11's are single turbo guys. The only people I ever see running 10's on a twins car are guys running around 15+psi of boost. I would run 10's on anything over 15psi to be safe. I've put many many miles on 10's with no problems at all. If you have a decent ignition amp they will stay nice and clean.

Just because Mazda ran 7's and 9's doesnt mean anything. That desicion was based on around 10psi of boost and 215ish rwhp. As you increase the hp you increase the combustion btu's and need to run colder plugs. I typically ran 9's from 12-15psi, then 10's from 15 or 16+.

On a side note, I run b10egv plugs (heat range 10)which you gap. I run a low gap of about .022 with them.

I'm sure there are some people on the forum that run a plug colder than they really need to, however if thier car is tuned and will idle good without fouling the plugs then it doest hurt anything. They are only making it more safe, nothing in the world wrong with that. I would VERY much rather run a plug too cold than too hot. That said, there are MANY MANY people on this forum running 10's and 11's because they need them...not just because they are paranoid.

Stephen

If your wanting to run 340rwhp I wouldnt run 7's.

The iginition amp does have its place and its not just to keep plugs clean. As you increase the hp obviously you increase fuel and air along with it. You need to combust that fuel and air very quickly and the more of it you pack in there the harder it is to combust. The ignition amp provides a stronger spark as well as increases the duration of the spark. At 340rwhp you can probably get by with no ign amp if you have very good tuning but why chance it? Running no amp and running hot plugs will increase your chances of pre ignition. You might be able to get by with it...but for how long?

Your copy and paste is correct, the #1 reason to run a colder plug is so that it doesnt retain so much heat. The plug itself is subjected to 1800F degree temps and as you can imagine that will create one damn hot plug tip. With the plugs retaining so much heat it will ignite the a/f mixture before its time and cause preignition. This is especially bad for the trailing plug which is why Mazda runs it colder.

Stephen

That makes a lot of sense, I'd never thought of it that way. Thanks Stephen!

-s-

I've heard many horror stories about KD and high hp, they just dont seem to mix well.

I cant imagine Ari telling someone to run 7's all the way around. Maybe it was for a particular situation with very low hp, or maybe he was talking about a N/A car. I dont know the specifics of the conversation. For a car running less than 12psi I think 7's and 9's are fine. Maybe he just told someone they could run the Rx8 7's in place of thier normal 7's but meant for them to keep 9's in T. I cant imagine he told them to do it all the way around, but I wasnt there to hear the entire conversation. I know that Ari has also suggested to Goodfella to run 10-11 race plugs in his car while at 16or so psi.

BTW - I meant to add something on my last post and forgot. The reason its worse for trailing to have preignition issues is because the rotor passes trailing first at a very very early point in the combustion process. You definatly wouldnt want to ignite that mixture that soon, thats why for safety Mazda runs 9's in trailing to make sure they dont get pre ign problems.

If I were going to be pushing 340rwhp I'd run 9's all the way around with an ign amp. No reason to chance it when you dont stand to gain anything. You'r idle should be fine with 9's, especialy with a amp. Personally, I dont amp the trailing. I just run a single MSD6a on the leading coil, its also a lot cheaper as a MSD6a can be had for $160 from Summitt racing

The bad thing about testing something like running 7's all the way around and no amp while trying to nail down 340rwhp is that your not going to know it didnt work well untill you have to spend $3000+ on a engine.

Stephen

I'm using the RX8 plugs. I haven't had any ignition cut problems since I put them in...

7's all around

why?