iridium spark plugs

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Peter Robinson · #1 Post by **Peter Robinson** » Mon Oct 29, 2018 7:09 pm

anyone know the part number/specs for NGK iridium tip spark plugs for a 356?
Thanks

C J Murray · #2 Post by **C J Murray** » Mon Oct 29, 2018 8:47 pm

I'm not sure they even make one for that application but I suggest you do not use iridium plugs unless you have a very hot ignition system. It takes a lot of juice to fire those consistently and reliably. A basic points system is better off with standard copper tips.

David Jones · #3 Post by **David Jones** » Mon Oct 29, 2018 11:01 pm

NGK 4085 is advertised as an Iridium IX plug and is correct for a 356 dimensionally. Also listed as a BPR6HIX. The straight NGK BP6HS is as good as any plug I have used however.

http://www.sparkplug-crossreference.com ... PN/BPR6HIX

Tom Wavrin · #4 Post by **Tom Wavrin** » Tue Oct 30, 2018 3:30 pm

CJ knows way more than I will ever do about anything 356 so respectfully accept his opinion concerning the iridium plug vs standard copper core. But, I changed over from std copper to the iridium BPR6HIX this Spring and am impressed with their performance, specifically how appropriately they are burning by the look of the plugs when I pulled them to look last week for my Fall oil change. A testament, I suppose, to the condition of my car's electrical and fuel systems - thanks in part to the advice provided by this forum. No special add-ons as my car is stock. Note that the BPR is an extended tip plug vs BR which is standard tip - must make sure you have piston to plug tip clearance to use 'em.

Jeffrey Leeds · #5 Post by **Jeffrey Leeds** » Tue Oct 30, 2018 3:57 pm

Cliff, I'm surprised to learn that the iridium plugs need a special ignition system. I've used these in my engine for the 8 years I've owned the car with no issues. I guess my engine is even better than I thought it is. ;>)

C J Murray · #6 Post by **C J Murray** » Tue Oct 30, 2018 5:49 pm

Always be a skeptic even when you read what I post. I am sometimes wrong. I believe that I read what I posted on an NGK tech article. I need to look for that and post it if I can find it. NGK actually uses nickel for the standard plugs. The idea of using other metals is to reduce the diameter of the electrode so that the spark kernel is not trapped between the electrodes. Platinum and iridium wear very slowly so they can be made thinner than the nickel center electrodes. The same idea is behind the use of pointy ground electrodes. Sometimes articles contradict each other.

Here is something to read while I try to find the other article but it is pretty dated. Note that twin plugs have issues according to Champion.

https://www.vdlfuelsystems.com/anything ... ark-plugs/

Heidi Frances · #7 Post by **Heidi Frances** » Wed Oct 31, 2018 12:29 pm

I A-B'd a set of Bosh Copper and Platinum plugs in our '58 and the idle was noticeably better with the Platinum. Now, Could be lots of things, huh? Gap and such, but the Platinum plugs work well for me.

Franny

C J Murray · #8 Post by **C J Murray** » Wed Oct 31, 2018 12:32 pm

It's not looking good so far for my suggestion to not use iridium plugs. I am still looking. I did find an older MSD tech recommendation that fine wire plugs do not hold up when combined with MSD ignitions but now I see that they have added iridium plugs to their line.

I also found this article which refers to the strong opinions expressed on forums not being correct so there is conflicting data out there.
https://www.turnology.com/tech-stories/ ... m-opinion/

I have used all types of plugs in my street and race engines and I can't say I have ever felt a difference. I do find that NGKs are the most durable.

C J Murray · #9 Post by **C J Murray** » Wed Oct 31, 2018 12:48 pm

Here are 2 iridium 9 heat range NGK plugs from my race car. The 1 plug would indicate that the engine was running fine but apparently the other cylinder was very unhappy. This would tend to support the old recommendation from MSD to not use fine wire plugs with their ignitions. I don't know what happened but I am using surface gap plugs now.

Jack Walter · #10 Post by **Jack Walter** » Thu Nov 01, 2018 11:23 am

From what I have read about Iridium plugs they work very well with fuel injected cars where the mixture is very precisely controlled within certain limits but are prone to fouling in cars with carburetors where the fuel/air mixture can vary pretty widely.
This seemed to be the case when I tried Iridium plugs in my Carrera - even with a CDI ignition system I was having issues with plug fouling that was greatly reduced when I switched back to a more conventional spark plug design. The research I did led me to believe that the actual working heat range of the Iridium plug seems to be narrower than that of the more traditional platinum or copper spark plugs. I've always had very good luck with NGK and Bosch Platinum in my pushrod Porsche engines.

C J Murray · #11 Post by **C J Murray** » Thu Nov 01, 2018 11:29 am

Thanks Jack, but where have we both read that? I'm still looking.

Tom Wavrin · #12 Post by **Tom Wavrin** » Thu Nov 01, 2018 1:52 pm

My experience with the iridium vs copper core NGK plugs coincides with Franny's in that the idle increased 50 - 75 RPM, whatever that means.

Jack Walter · #13 Post by **Jack Walter** » Thu Nov 01, 2018 3:10 pm

C J Murray wrote:Thanks Jack, but where have we both read that? I'm still looking.

On the world wide web somewhere... therefore it MUST be true - right?

I don't remember where we found that little bit of information - but I switched back to Bosch Platinum and didn't have the issue with plug fouling that I was experiencing down at Amelia Island.

Phil Planck · #14 Post by **Phil Planck** » Thu Nov 01, 2018 5:21 pm

I switched to iridium in the 912 this summer. Cant tell any difference.

C J Murray · #15 Post by **C J Murray** » Thu Nov 01, 2018 5:51 pm

I'm digging deep now...

https://www.carsdirect.com/car-repair/c ... erformance

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