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Discussion Starter · #21 ·
Fantastic. I hope this clears it up for all of us with wet sumps and I expect (my thinking) that those of us with wet sumps and experiencing sluggishness or hesitance and have r8b plugs installed can look to the plugs as a first point of diagnosis
 
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this version of owners manual says 8C-H is for the 4.7

View attachment 137628
I have seen that before..It looks like they have this all jacked up...The 4.2 and the 4.7 have same part # for the plugs and the cylinder heads and that makes sense...You are not gonna want to cast another cylinder head from a 4.2 and a 4.7 sized engine if you are a manufacture...So the fact you have two different plug lengths doesn't make much sense IMO...J
 

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I just pulled one of mine..... 8-C but I'm going to try 8B anyway out of curiosity.
I have seen that before..It looks like they have this all jacked up...The 4.2 and the 4.7 have same part # for the plugs and the cylinder heads and that makes sense...You are not gonna want to cast another cylinder head from a 4.2 and a 4.7 sized engine if you are a manufacture...So the fact you have two different plug lengths doesn't make much sense IMO...J
Does it need to poke down a bit more into the cylinder coz it's igniting a slightly larger quantity?
 
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No, you don't want that in the least...That sharp edge makes a spot to help for detonation to occur...What is your car? This has been so back and forth I can't keep track...J
 

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No, you don't want that in the least...That sharp edge makes a spot to help for detonation to occur...What is your car? This has been so back and forth I can't keep track...J
oh ok. fair enough :)

my car is 2007 4.2 Auto and I understand OP's car is too. It does seem to be a replacement part.

This is a Dry sump cylinder head - I don't know what plugs are in it but you can see where there's room/scope to use the longer plug - I wonder what the reason for the change was - commercial or technical.

137641
 

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Discussion Starter · #26 ·
Mas430v4. You have a dry sump so a duo select (red covers)? I understand the 2007 came with both dry or wet (wet only in the zf/automatica). I'm curious whether the length-bore of the plug hole is the same with both heads. The 8c plug is longer and if the bore is the same depth, it should protrude further into the head but if the bore is longer in the "blue" head, the 8c plugs may end up being flush as with the above image. My only concern would be the longer plug in the dry sump head (red) may cause some interference, probably not, or pre-ignition? I may be way off here but will using a too-short plug cause issues with insufficient flame-spread during ignition?
 

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Mas430v4. You have a dry sump so a duo select (red covers)? I understand the 2007 came with both dry or wet (wet only in the zf/automatica). I'm curious whether the length-bore of the plug hole is the same with both heads. The 8c plug is longer and if the bore is the same depth, it should protrude further into the head but if the bore is longer in the "blue" head, the 8c plugs may end up being flush as with the above image. My only concern would be the longer plug in the dry sump head (red) may cause some interference, probably not, or pre-ignition? I may be way off here but will using a too-short plug cause issues with insufficient flame-spread during ignition?
no. 2007 AUTO <= ZF, wet, blue :)
As Jason said the heads are the same on 4.2 and 4.7 wet sump cars.

F1 (red, Duo Select, Dry sump, up to 2008) I don't believe is even in this conversation as the confusion is only around what plugs go in the wet sump head as we are both wet sump

And as it turns out, they both go! 8C-H is an official Maserati replacement part for 8B.
As the heads are them same, the only difference we will have is how much of the plug protrudes out of the head

I will soon find out the running difference as I am heading out now to buy 8 8Bs and will fit them later.

Sometimes I find my car can feel sluggish (up to now I had assumed it was just a characteristic that can be overcome with a heavier foot) and my car definitely makes some kind of tic tic tic noise under load that I have only ever heard before in my ignition advanced Fiat 127 30 yrs ago :) That's apples and oranges of course.

I know I have a noisy lifter and main dealer suggested it could be that evap valve that's attached to the body but I'm not convinced or possibly some kind of broken welds inside the header.
Friendly mechanic thinks it's an exhaust leak in the header.

I'm willing to throw new (old!) plugs at it and see what happens
 
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oh ok. fair enough :)

my car is 2007 4.2 Auto and I understand OP's car is too. It does seem to be a replacement part.

This is a Dry sump cylinder head - I don't know what plugs are in it but you can see where there's room/scope to use the longer plug - I wonder what the reason for the change was - commercial or technical.

View attachment 137641
That doesn't look correct.. The plug should thread all the way into the CC...J
 

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so look where my unnecessary experiment has gotten me - all going great, 4 of 8 cylinders done, then this on no 4 (the most difficult one, and therefor the one I thought I was being most careful)...:
This is a brand new plug, and I was only starting to get tight.
I think I'm f***ed ?
 

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No, you just need an extractor to pull out the rest of it...I have had this happen several times over the years...J
 
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No metal bits...You need this in the correct size...Recognize you need a tap socket to turn it as it is square..J
137646
 

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ok - thanks Jason, heart attack over. Got a tool to extract that bit of plug - whew!
137668


Just need to button it back up now - firewall off allows for further one-sided A/C investigation and fix creaky wiper - it's an ill wind that blows no good. Plus I found my manual in all the tearing house apart looking for tools. For what it's worth that said NGK-PMR8A (!!)
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Discussion Starter · #36 ·
Mas430v4. Happy to see you got it out safely... and further confused by your manual stating the use of 8A, although as previously stated, they "both go" so wondering if 8c is the replacement for 8b and if so, why? Let us know if you any difference.
 
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