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Marnal Head and NGK Spark Plug Thread Depth


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#1 86mightymax

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Posted 31 January 2020 - 11:01 AM

Hello. I am trying to determine what spark plugs to use in my AMC Marnal NJV head. I currently have NGK BPR7ES plugs installed, but from what I've read, the threads with these plugs are sticking down into the combustion chamber about 1/4". Albeit an old post, the information wouldn't have changed. I can't see those photos, and inwas slightly confused as to what plugs Art ended up going with. He hasn't logged on since 2017, so I don't imagine he will be chiming in. I have a Magna MPI, so I do believe that "7's" are a good starting point. I'm concerned with the thread depth. I don't want to leave a spot for carbon to build up, cause detonation, or any other issues related to the long protrusion. Any help is really appreciated. I apologize if I didnt post in the correct place.





#2 psu_Crash

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Posted 31 January 2020 - 11:55 AM

I ran BUR7EA in my AMC Marnal for many years without an issue. I do remember the post you are talking about, but I wouldn't be worried about it

Just noticed your location. You're less than a 2 hour drive away. Hello Neighbor!

Edited by psu_Crash, 31 January 2020 - 11:56 AM.

'86 Starion, MPI with MS2extra, Turbo Lab GTX3071R, P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods, AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
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#3 86mightymax

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Posted 31 January 2020 - 01:43 PM

Really? Where are you at? I'm in Moravia, near Cortland, Auburn and Ithaca.

#4 psu_Crash

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Posted 31 January 2020 - 02:01 PM

Just south of Corning on the PA/NY border
'86 Starion, MPI with MS2extra, Turbo Lab GTX3071R, P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods, AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
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#5 86mightymax

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Posted 31 January 2020 - 03:25 PM

Small world! I'm going to order some of those plugs! Thanks!

#6 kev

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Posted 02 February 2020 - 04:05 PM

I run the same plugs as psucrash in an AMC marnal head. I never measured the protrusion though

#7 psu_Crash

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Posted 03 February 2020 - 02:49 PM

I have an AMC Marnel on the shelf. Hit me up in a couple months and I can measure then. Right now the basement is a paintbooth and I can't get to anything lol
'86 Starion, MPI with MS2extra, Turbo Lab GTX3071R, P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods, AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
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#8 psu_Crash

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Posted 03 February 2020 - 02:49 PM

I have an AMC Marnel on the shelf. Hit me up in a couple months and I can measure then. Right now the basement is a paintbooth and I can't get to anything lol
'86 Starion, MPI with MS2extra, Turbo Lab GTX3071R, P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods, AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
2016, 17, 19 SCCA Solo, Glen Region Season Champion in Street Modified
The Valencia Project
http://www.starquest...+golden +dreams
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#9 importwarrior

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Posted 04 February 2020 - 06:14 AM

I would like to know if there is a difference in thread length between the NGK 7031 and the plugs he mentioned?


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#10 psu_Crash

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Posted 06 February 2020 - 08:28 AM

View Postimportwarrior, on 04 February 2020 - 06:14 AM, said:

I would like to know if there is a difference in thread length between the NGK 7031 and the plugs he mentioned?
I've had them side by side and saw no difference in thread length
'86 Starion, MPI with MS2extra, Turbo Lab GTX3071R, P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods, AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
2016, 17, 19 SCCA Solo, Glen Region Season Champion in Street Modified
The Valencia Project
http://www.starquest...+golden +dreams
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