Iridium Spark Plugs in a MFI car?

[Tonger]

Hello,

I have a '72 911s that needs (and will get) a tune and tends to foul the normal Bosch spark plugs with around town driving.

Given I'm taking these things out to clean them, would it be a good idea to just replace them with Iridium type plugs from NGK/Denso etc?

Supposedly, the iridium plugs are less prone to fouling which would help with starting. Does anyone have any experience with this?

I was looking at something in the 8 heat range - BPR8EIX in the NGK plug since I live in the South.

Any advice, insight, part #'s or ridicule would be welcome.

Thanks!

[gled49]

Unless it is a race car, that is pretty cold. You didn't say what model you have? BP6ET is a good plug for S/RS, it is a 3 ground plug.

[Lash LaRowe]

I have been fighting the same problem with my 72 S (with MFI) and using Bosch W3CS plugs that are constantly fouling. Gled suggested using BP6ET plugs, I looked at Advance Auto parts but their check to fit says BP6ET is incorrect for a 72 S ??

Just recently I was looking over the MFI check measure and adjust pamphlet and I discovered that the 2.4 engine should only use 87 octane fuel. I have been using 92 octane. This may be a big factor why the plugs are wet.

Lash

[HarryD]

Lash, don't know anything about plugs but a higher octane fuel is not related to your problem.

[Chuck Miller]

Hmmmmmm ... I've been using the cheap Bosch WR5-DC with no problem for years.........

[edmayo]

I've been using BP7ES for around 25 years or so, in both my 2.4S with MFI and my 67S with carbs. (also Bosch CD ign.) if that says anything. For the 67 S I nearly always run 93, for the 72, if I'm putting around town, 87, if fast highway, 89, if autocross, usually 89, sometimes 93. And I know, shouldn't really need the higher stuff no matter what,,,,just gives me the warm fuzzy!!

[gled49]

Spark plugs were chosen by Porsche to protect the engine against extreme abuse, like sustained speed on the autobahns, way to cold for driving in America. Chucks Bosch 5 heat range is a good example.

[RSTarga]

I've been running BR7EIX with no problems.

[Tonger]

Thank you for your feedback and suggestions. I called the tech line at NGK today and asked about an iridium plug. The consultant recommended a BPR8EIX for that specification.

I went ahead and ordered the BPR7EIX which is one heat range hotter like the BP7ES that Mr. Mayo recommends and is also similar to RS Targa/David's recommendation. The recommended gap for 10:1 compression was 0.32 which is what the plug is out of the box. I also asked him whether the heat ranges transfer between the copper/nickel products and the iridium line and he said yes. Hopefully that means that the BPR7EIX will work ok and be less subject to fouling.

[RSTarga]

I went back and checked my last service. Looks like they switched from the BR7EIX to the BR8EIX, so maybe they noticed something?
What is the difference between the BPR designation and the BR designation?
The original plug for the S was the Bosch W265P21. They were very expensive plugs back in the day, like $20 dollars each in 70's dollars.
I run 92 Octane premium.