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Discussion Starter · #1 ·
So I did some searching, and I decided that the Denso Iridium plugs for the 91 miata was the plug of choice. My question is what gap should give me the best result?
Mods I have that might affect your input:

AdamTurbo chip
15 psi on the stock turbo
2" IC piping (if that matters)
MSD blaster2 coil
 

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You know, the part number for the Denso iridiums for the 91 miata is exactly the same as the one for the 91 MX6-GT? I dunno if they make the miata longer or the mx6 version longer but there is something to look at. If they're both the same, you'll wanna look for the IK22 (stock #5310) instead of the IK20s (stock #5304) you were looking at, since the IK22s will be the colder heat range.

The main reason you'd want to check this out is the thread reach. NGK makes sure that the end of the threads match up almost perfectly with the combustion chamber. The thread reach on the Miata is shorter than that of the one for the 6. This should create an issue in higher-cylinder-pressure engines since we all should know that sharp ends in the CC get hot, and when they get too hot they lead to detonation. if the thread reach leaves a sharp edge around the spark plug, that's not such a great thing.

In all reality, I don't think it's a huge issue, it's just something to be aware of.

Oh, and Denso recommends a gap of .032 for the colder heat range. Seems like they might know what they're talking about...:)
 

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hot/cold plugs

As HotRodMex stated, manufacturers usually have both types of heat range available, depending on your driving requirements.

Try to match up the "original" NGK with the Denso plug's overall measurements. As far as the gap, I'd go with the stock OEM recommendation of .040". (With your mods and today's higher energy ignition systems, too close of a gap may burn off quicker.)

PS, It's been documented in the past that upgrade platinum plugs and such, prove no real lasting benefit for "Turbo" powered cars. But, it's your money !
 

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Discussion Starter · #4 ·
Re: hot/cold plugs

johniebgoode said:
PS, It's been documented in the past that upgrade platinum plugs and such, prove no real lasting benefit for "Turbo" powered cars. But, it's your money !
I'm not looking for longevity, my main goal is performance. Even if I have to replace the plugs every year. When it comes to things like this, I don't mind spending money.
 

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Acctually, Iridium has proven to be longer lasting than platinum, while providing a better spark kernel. Document problems have been with Platinums only. you will find no one with a bad experience from iridiums (of course, no would be the time for them to come out and say so). There are a few high boosting memebrs who like theirs. Especailly the fine wire iridiums like Denso's (NGK has a large electrode iridium, as well as a fine wire line, called "iridium IX"). In reality, you'd be looking at these plugs going 30-50k before changing, with platinums going 15-20k, and regulars going 7k. Of course, these values are not the complete service life of the plug, but the point at which you should replace them to maintain performance, especially with FI.
 

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SixSick6 said:
every year? I replace mine every 2nd oil change :lol:
I replace my V-powers every time I change the oil (Mobil1 @ 7k miles. Filter @3.5k). I can feel the difference even in that short interval, mostly in how smooth the engine runs.
 

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Not sure if it matters to you guys, but I run a .028 gap on Miata plugs from NGK on my FE3 & 15psi.
 

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SixSick6 said:
we change our oil the same way :lol:
I just can't wait until I can go PAO synthetic like Redline or RoyalPurple and do my oil change once per year.
 

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Discussion Starter · #12 ·
From what i've heard and what i've seen Amsoil is just as good as Royal purple or Redline.
 
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