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WOT Junkie and avid corn burner
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Discussion Starter #1 (Edited)
What spark plugs do y'all use? What gap spec do you run? When RobertP did my head swap, it supposedly ran like crap with the Autolite AR94's, although they were used for at least 10-15 thousand miles prior to the swap. It pings noticeably in the low RPM's with the TR6's that I use now.
 

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50 years of Mercury Cougar 1967/2017
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PM me.
 

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Super Moderator
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Mine are NGK.

Ask Rob what you need and what to gap them at ... My gap is going to be different than what you need.
 

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WOT Junkie and avid corn burner
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Discussion Starter #4
What gap works best with these heads at 11.2:1 compression? Any takers?
 

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Premium Member
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What gap works best with these heads at 11.2:1 compression? Any takers?
I'd be willing to say around 0.35-040 spark plug gap!

The SC cars about .032.
 

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WOT Junkie and avid corn burner
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Discussion Starter #7
So I could probably open them up a bit. I've been running them at .044", roughly.
 

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WOT Junkie and avid corn burner
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Discussion Starter #9 (Edited)
What are y'all's thoughts on the TR6IX plugs?

Or Autolite XP103 plugs?
 

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That's way too tight. Nowhere near the cylinder pressure in 11:1 n/a compared to a typical boosted car. 0.045" to 0.050 should be more than adequate.
That's interesting. I've been running mine at .035 for years NA on the stock PI and stock shortblock without any issues and on the spray as well for years.

Hasn't seemed to hurt it. I'd think that the TFS would not have an issue with it either.

You are correct that the gap needs closed up even more on a Supercharged-Turbo application to prevent spark blow out.

I do think if he is around .44 then that shouldn't really be an issue. May be a timing issue or not enough fuel.

Just my opinion.
 

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That's interesting. I've been running mine at .035 for years NA on the stock PI and stock shortblock without any issues and on the spray as well for years.

Hasn't seemed to hurt it. I'd think that the TFS would not have an issue with it either.

You are correct that the gap needs closed up even more on a Supercharged-Turbo application to prevent spark blow out.

I do think if he is around .44 then that shouldn't really be an issue. May be a timing issue or not enough fuel.

Just my opinion.
It definitely won't hurt it, but that doesn't make it optimal either. Just like anything else on these cars, spark plug gap was specified for non-optimal conditions just like the fueling and spark tables, which is why I ran 0.065" gap in my PI head swapped engine. Even then it's probably the least critical parameter out of fueling, timing, and spark gap, within reason.
 

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WOT Junkie and avid corn burner
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Discussion Starter #12
Now how about running Autolite XP103's and NGK TR6IX's?
 

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WOT Junkie and avid corn burner
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Discussion Starter #14

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What'd I tell you. Get the NGKs or Motorcraft. Ask Rob for the exact type.
 

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It definitely won't hurt it, but that doesn't make it optimal either. Just like anything else on these cars, spark plug gap was specified for non-optimal conditions just like the fueling and spark tables, which is why I ran 0.065" gap in my PI head swapped engine. Even then it's probably the least critical parameter out of fueling, timing, and spark gap, within reason.
LOL! So what then do you suggest as optimum for my new combination. I need your wisdom.
 

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Rob said the AR94's made it run like crap.
I don't see why they wouldn't work. 11ish:1 is not out of this world that would necessitate some special spark plug. Are you absolutely positive they were all gap'd correctly? The offset ground electrode will not be 100% on the mark if you use a standard gap tool or feeler gauge perpendicular to the center electrode. To properly set the gap on these you have to angle which ever tool you're using just a tad, otherwise, the gap WILL be larger than what the tool says.

Say you use a feeler gauge or a gap tool from the parts store to check the gap like so:



Shows ~0.034" gap, roughly.



This is the real gap (without having moved the ground electrode at all):



Around ~0.050".





Perhaps all this was indeed taken into account, but can't assume anything.:)
 

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WOT Junkie and avid corn burner
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Discussion Starter #18
That's kinda how I did it. I pulled a few of my tr6's out, looks like they are the correct heat range. Assuming there was an AR in the same heat range as the tr6, any reason to choose the AR style plug over a normal style copper plug?
 

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WOT Junkie and avid corn burner
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Discussion Starter #20
One
 
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