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Discussion Starter · #1 ·
as a number of searches brought up unanswered questions and others brought up answered questions, but...

Pulled the front four plugs last week to check on condition as I think I have a slight stumble. They looked clean enough. The plugs are NGK PMR8B
One of the resources suggests PMR8B for manual transmissions (Due Select)
and PMR8ch for Automatics.
Both are gapped at .028

My plugs seem to be gapped at .026-7.

So, should I be replacing with PMR8CH?

I don't know what the diff is and cant find it on the ngk site.
 
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Automataic cars are wet sump and F1 cars are dry sump...The cylinder heads are different along with a lot of components...You need to have the correct plugs..You don't normally gap plugs these days especially fine wire plugs like these...Jason
 

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as a number of searches brought up unanswered questions and others brought up answered questions, but...

Pulled the front four plugs last week to check on condition as I think I have a slight stumble. They looked clean enough. The plugs are NGK PMR8B
One of the resources suggests PMR8B for manual transmissions (Due Select)
and PMR8ch for Automatics.
Both are gapped at .028

My plugs seem to be gapped at .026-7.

So, should I be replacing with PMR8CH?

I don't know what the diff is and cant find it on the ngk site.
I believe the difference is the length.
It would help to know what your driving without checking your other threads.
If you have the owners manual it will tell you what plugs you need.
 

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Discussion Starter · #4 ·
I have an exec model. The c-h have a longer reach than the b. Here's a comparison NGK.com: Compare Products
So, if the previous owner installed the B plugs then possibly the combustion isn't as efficient as it should be as the electrodes are 3mm short. As for the manual, seems pages 246-261 are missing and the plug reference is in there I think.
 

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Discussion Starter · #5 ·
O.K. So reading through as many threads as I can regarding proper plugs for the 07 wet sump versions and there are discrepancies with thread opinions, manuals and guides, and so-on.
So, it seems that the duo select-dry sump engines (always 4.2) use the shorter ngk pmr8b plugs (19mm) versus the wet sump engines should use the pmr8c-h (22mm) plugs and the Denso plugs are 19mm and not correct for the wet sump engines?

So, using the shorter plugs in the wet sump version (blue valve covers) may work but possibly reduce performance
and the question is: if someone mistakenly puts the longer plug in their dry sump (duo select/red valve cover), will the 3mm impact the piston and cause damage? This is just a question to help clear up confusion and prevent problems.
Jason had an interesting image in one thread showing the head and a short plug but that thread became more confusing as it went on....

This is an important issue to clear up, I think.
 
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The Denso plugs don't cross reference correctly...Just use the correct NGK ones for your model.....You never want to use a longer plug..Not sure if it would damage it at 3MM probably not, but not a good thing..J
 

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Discussion Starter · #7 ·
Yep. I realize I should use the plugs for my car BUT the problem is confirming which of the NGK are right for the wet sump 4.2 engine in the Quattroporte Automatico!!! From the many posts o the subject, there seems to be confusion in the forums and also written reference materials.

Quattroporte Due Select 4.2 (Red covers) use=
Quattroporte Automatico 4.2 (Blue covers)=
 
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PMR8B is for dry sump 4.2s....PMR8C-H is for 4.2 autos....That came from an owner's manual and a shop manual....Jason
 

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Discussion Starter · #9 ·
That's good to hear. My repair manual (owners manual missing the pages covering spark plug) only mentions pmr8b, even in the repair section for the 4.2 wet sump. Your shop manual must be correct.
 

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Discussion Starter · #11 ·
Thanks Mas4304v but as I mentioned, the above conflicts with other information. the prior post from Jason states pmr8c-h is for 4.2 Automatica. Another 2006-2007 manual states pmr8a or B but only shows the duo select motor (Red). Hence the confusion. All of this is making me nervous (again) about fitting the 8c-h plugs as they are 3mm longer..
 
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PMR8B is the plug for dry sumps...We are resealing a front cover on a dry sump right now and I just had my guy pull a plug...Jason
 

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Discussion Starter · #13 ·
PMR8B is the plug for dry sumps...We are resealing a front cover on a dry sump right now and I just had my guy pull a plug...Jason
PMR8B is the plug for dry sumps...We are resealing a front cover on a dry sump right now and I just had my guy pull a plug...Jason
PMR8B is the plug for dry sumps...We are resealing a front cover on a dry sump right now and I just had my guy pull a plug...Jason
I believe you. The conflicting info in manuals is causing the confusion/. Do you have a wet sump handy to confirm the longer plug is not an issue? That would seal the debate.
 
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I have a wet sump in the parking lot that needs variators..I'll pull a plug this AM..J
 

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Discussion Starter · #15 ·
Thanks but let's hope that car has the right plugs to start with. I found 8b in my wet sump Automatica and judging from the confusion surrounding rear pads; an experienced shop received the wrong ones twice despite using my VIN to source, confusing plugs wouldn't be a huge surprise. Thanks for your input.
 

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yep - I just wanted to "document the confusion" so to speak.

Your manual that had the spark plugs section torn out might be from a dry sump car and and whoever did that knew it and on one level protecting you from making a mistake :unsure:

And you think I can find my manual?! I had it out only the other day.... :mad:
I am changing my plugs too so I will be interested to see what I have (07/WS) versus you and Jason's sample
 
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PMR8C-H is the wet sump plug and it 3mm longer...Hope that settles your internet battle..J
 
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My wet sump car I have here is a 4.2 and has the PMR8C-H in it...Parts catalog shows same part# for 4.2 and 4.7 cars...239242....J
 
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