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Discussion Starter #1
I've seen a few comment that the full thread plugs protrude farther into the combustion chamber,and can be a problem with detonation from that.Well,I knew that they did not, so I snapped a few pics to show that they do not.
plugs being compared:
Stock replacement Autolite 764-PP,and the Autolite 103:


Stock replacement 764-PP in the combustion chamber:


Autolite 103 in the same combustion chamber:


JL
 

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Thanks JL

Some months ago, FoMoCo started this with their plugs (through the Motorcraft line) and could not believe how many guys would not believe that they would not cause a problem. I should have thought about finding me a head around here and taking some pics. I hope this will help some out there to believe there is no problem with this now.
 

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Great pics. Thanks for clearing that up... I still have a few concerns as if the Full length plugs would seal as well as the half threaded plugs? And it stands to reason that you possibly could force the full threaded plug to be screwed in further if you really tried. I know some people do tend to overtorque things a bit.
I used to and have learned my lesson ;)

Okay, then if the longer thread doesn't matter than it must just be the type of plug which can cause problems.
For me the NGK TR-6 plug did cause some major problems with my particular application. Major Spark blowout above 5600-5700 rpms and detonation at WOT... So it wasn't the Full vs. Half thread but the plug itself. After I swapped plugs to the Motorcraft AWSF 22C's(Half Thread plug) the Sparkblowout was gone as well as the detonation. And I gained 40HP on the Dyno with just changing plugs and no other mods...

Also I did read about not being able to use the half threaded plugs in heads that require the Full threaded plugs. It was in one of the Mustang magazines... Either 5.0 or MM&FF... Just don't remember the issue. But it was during a head swap article.....

I have never tried the Autolite's and might give them a shot the next time I swap plugs just to see what the effects are. One thing is for certain, I will never ever use the NGK TR-6 plugs again!! And I don't recommend them in any of our cars.. at least not the Supercharged ones.....

Thanks again for the pics and post.....

Tom in Indy
 

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Sting said:
And it stands to reason that you possibly could force the full threaded plug to be screwed in further if you really tried.
Doesn't the plug seat on the angled shoulder? If so, you couldn't force the plug any further into the head. Once it hits the shoulder, it stops. If not, well...I sit here corrected. :D
 

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Discussion Starter #5
PhatDoggy said:
Doesn't the plug seat on the angled shoulder? If so, you couldn't force the plug any further into the head. Once it hits the shoulder, it stops. If not, well...I sit here corrected. :D
That is correct...The shoulder is where the plug stops threading.As for the heads that require a full-thread plug,those have a shortter thread,and it's closer to the shoulder area,so the half-thread plugs do pose a problem there with engaged thread count.
JL
 

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Again, very nice! And this cleared up a lot of my confusion...

Thanks again for clearing this up once and for all.....
 
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