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Discussion Starter · #1 · (Edited)
I previously posted regarding my install of iridium plugs in my 2014 classic. I offered to post a follow up after last season of riding, well here it is. I Only put 1600 miles on the iridiums. The bike is noticeable crisper at launch and slightly crisper on overall up throttles, that’s for sure. I pulled all four iridiums to take a look. Perfect coloration of the electrode and porcelain. Even the bottom two plugs were outstanding. . Then I gently cleaned up the flat section on the base of the thread reach. I gently checked the gap and reinstalled. Be forewarned the center electrode is a thin piece of wire and easily damaged. The proper iridium plug is an NGK CR8EIX (4218).

As a comparison-- I don’t know how long the previous MAR8B-JDS plugs were in. The top plugs were ehhh.. OK. The bottom ones were moderately fouled.

Here are the complete specs on the two plugs for comparison. The only difference of possible consequence that I saw is the protrusion after the thread reach. There is a 3mm difference in length. This extension is supposed to place the flame kernel at an optimum position in the combustion chamber. My research told me that one can use a “shorter electrode position in a longer spec application, not vice versa. It is not recommended to use a shorter *projection if any cylinder threads are left exposed after plug install. In our case it’s a non-issue the reach is ¾ for both plugs. The cylinder threads are all mated to spark plug threads. Goes without saying that was solid engineering in specifying a spark plug for the RNT was done. But I will tell you this. On a handful of my previous bikes The OEM recommended plug by far was not the best.
*technically protrusion is to the end of the center electrode (tip). More tip exposed on the MAR8. On the IR plug the bottom of the grounding electrode is about where the tip of the center electrode is on the IR. ......clear as mud. :)
In any event the patient survived and is flourishing nicely.

Give them a try and let us know what you think.

CR8EIX (4218) IR 4218
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MAR8B-JDS 8765
Rectangle Font Parallel Circle Pattern


Protrusion
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@Juice - thank you for the cataloguing of your experience with Iridium plugs. I just recently put them in and I am very pleased with the performance of them. It is as you have stated above. (y)
 

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The bike is noticeable crisper at launch and slightly crisper on overall up throttles, that’s for sure.
Sorry to be a doubting Thomas (or whatever the phrase is) but its been shown again and again (by anyone except those making and selling them) that iridium plugs don't do anything on the dyno that a set of new standard plugs will also do.

They were designed for and are good at extending the life of plugs, as the electrodes last longer but that's about it. Most people replace their bike plugs at the service interval regardless of the type, so even that benefit is usually wasted.

Basically, they are an expensive way to get a placebo boost for your bike.
 

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@Foxster - everyone has a right to their own opinion. You should try them yourself, or you'll always be left to believing the doubting crowd. I decided to try them myself, so now I know for myself.

I paid $8.50 US per plug, and I'm never going to have to change my plugs again! I fail to see where the term expensive can be used here.

The beauty of Iridium plugs is they last longer than any other type of plug, maintaining their (start, burn, and combust) characteristics longer than regular plugs. Regular plugs degrade quicker, which leads to sluggish cold starts, and degraded performance overall.

When you put Iridium plugs to work they bring back your engine to its optimal performance level, nothing more on the dyno than when new, just better than the guy still running with regular plugs.
 

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Discussion Starter · #7 ·
Sorry to be a doubting Thomas (or whatever the phrase is) but its been shown again and again (by anyone except those making and selling them) that iridium plugs don't do anything on the dyno that a set of new standard plugs will also do.

They were designed for and are good at extending the life of plugs, as the electrodes last longer but that's about it. Most people replace their bike plugs at the service interval regardless of the type, so even that benefit is usually wasted.

Basically, they are an expensive way to get a placebo boost for your bike.
I don't make them nor do I sell them. You won't meet a more skeptical consumer than me.
Brutal tractor work in the yard. I check the plugs every season. 5 years and they are fine. I do use them in a variety of machinery and like them. No magic boost in HP. Why would you expect that? Nothing wrong with sticking with the OEMs, enjoy.
 

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Thanks for the nice write-up, @Juice . 👍

To me any price difference is worth the saved pain in the neck of more frequent maintenance. If there's a performance benefit too, well, great!

BTW, my old 6th gen. Honda VFR spec'd iridium sparkplugs, and they lasted a long, long time.
 

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When you put Iridium plugs to work they bring back your engine to its optimal performance level, nothing more on the dyno than when new, just better than the guy still running with regular plugs.
They are simply not better in any way, shape or form than regular plugs. Independent test shows they don't make an engine start, run or perform better.

I tried them more than once over the years until I started dyno-ing my bikes and realised they make zero non-placebo difference.

They are useful for car sellers to be able to extend the life of plugs so that they don't have to replace them at service time i.e. it saves dealers some money. However, they do degrade over time and if you want to keep your bike running at it's best then you are better fitting new cheap stock plugs at the service interval.
 

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They are simply not better in any way, shape or form than regular plugs. Independent test shows they don't make an engine start, run or perform better.

I tried them more than once over the years until I started dyno-ing my bikes and realised they make zero non-placebo difference.

They are useful for car sellers to be able to extend the life of plugs so that they don't have to replace them at service time i.e. it saves dealers some money. However, they do degrade over time and if you want to keep your bike running at it's best then you are better fitting new cheap stock plugs at the service interval.
Your missing the point @Foxster …. He replaced the original plugs because of performance issues with the old ones and witnessed an increase in performance with the new plugs …. any New plugs, these happened to be iridium, no better than any other New plug ….. in this case just NEW ….. except ..(The Point your missing).. they will stay that way (NEW) longer….. purportedly anyway … ………………… Blitz ……….Six & 1/2 Dozen.. Same/Same
 

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Your missing the point @Foxster …. He replaced the original plugs because of performance issues with the old ones and witnessed an increase in performance with the new plugs …. any New plugs, these happened to be iridium, no better than any other New plug ….. in this case just NEW ….. except ..(The Point your missing).. they will stay that way (NEW) longer….. purportedly anyway … ………………… Blitz ……….Six & 1/2 Dozen.. Same/Same
Fair enough if that's the case, it matches what I've found. It was not how I read it though.
 

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…. any New plugs, these happened to be iridium, no better than any other New plug ….. in this case just NEW

They're more expensive - they must be better 😇
Anyway, used them on my R11S with it's bad electrification and they gave a better and longer performance same as @Juice mentioned.
Especially at a start up that I felt more quickly. Yet not tried on my 9T since I'm fine witht the OEM's/Standaed and had no issues since.
 

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Thanks for the nice write-up, @Juice . 👍

To me any price difference is worth the saved pain in the neck of more frequent maintenance. If there's a performance benefit too, well, great!

BTW, my old 6th gen. Honda VFR spec'd iridium sparkplugs, and they lasted a long, long time.
Agreed @TimC - and because the bike jumps to life so quickly on start-up, I'll bet that battery life is also extended, another win for the Iridium's!!
 

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Discussion Starter · #15 · (Edited)
They are simply not better in any way, shape or form than regular plugs. Independent test shows they don't make an engine start, run or perform better.

I tried them more than once over the years until I started dyno-ing my bikes and realised they make zero non-placebo difference.

They are useful for car sellers to be able to extend the life of plugs so that they don't have to replace them at service time i.e. it saves dealers some money. However, they do degrade over time and if you want to keep your bike running at it's best then you are better fitting new cheap stock plugs at the service interval.
eeehhhh, wrong....they are better.

Must be a hell of a placebo with the overwhelming positive reviews.
Just as many independent reviews cite better performance and easier starting amongst other things. Personally I felt no performance improvement but as I wrote the bike undoubtably felt crisper.
Again I have had many bikes where a spark plug other then OEM were better. The one that stands out for me was a 98 Fat boy. I had mild engine work done by a Harley authorized dealer. He assured me the stock plugs are fine. After the build I tried 5 other plug varieties and sure enough one of those (same heat range) demonstrated as better. The bike jumped off idle far better then the OEMs. As a note these were non iridium plugs. Fact is many of us with the RNTs re-pipe and re-map. OEM plugs might be the best for the new set up. Yea they work ok but maybe not the best.
Anyone have to gorilla out OEM plugs in this bike?
The longer protrusion into the combustion chamber gives more area for carbon to build up. My bottom plugs took way more effort to get out than expected. As I removed the lowers I thought they would break. I watched a video on U-tube of the last spark plug change ON MY BIKE before I bought it. And a torque wrench was used correctly by the original owner.
The plating (or lack thereof) on the spark plug shell that screws into the cylinder head is another difference that should be considered when comparing different brands of spark plugs. Nickel coatings on the iridium spark plug shell and threads helps prevent the threads on the plugs from sticking to those in the cylinder head. A BIG PLUS.
A spark plug with an un-coated plain steel shell or even one with a black oxide coating won’t provide the same degree of anti-seize and corrosion protection.

Performance? Some yes some no I recon. Just as many videos and reviews showing performance gains as not.
 
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