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#1
09-21-2008, 11:00 PM
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Re: NGK Spark Plugs
Just called Advanced, and they listed the GR5 for an L72, and have them in stock. Since I dropped my compression to 9.75 to run on pump gas, do I need to go to one range hotter? Would that be GR4?
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#2
09-22-2008, 05:57 PM
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Re: NGK Spark Plugs
The 5/8" hex won't matter...in fact, it makes them easier to get a socket on...seems I had 'em listed as 13/16" hex, instead of the correct 5/8", but I fixed it: click
The hotter plug may indeed be better...
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#3
09-22-2008, 11:52 PM
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Re: NGK Spark Plugs
Well, the thread diameter was smaller, too. I figured the 5/8 must be for 14mm and the 13/16 for 18mm....not sure about that, but I know I would have needed a LOT of pipe dope to get them to seal!!
 Just called Advanced, and they stock the GR4's. Thanks for your help.
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#5
09-23-2008, 12:06 AM
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Re: NGK Spark Plugs
the 291 used the 840 plug for the early part of the model year, then switched over to the peanut plug
__________________
70 L78 Nova Fathom Blue,Bench, 4spd, F41, 3:55 71 Porsche 911 Targa
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#6
09-23-2008, 02:00 AM
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Re: NGK Spark Plugs
They both used 14mm threads...in fact, if it's an original carb'd sbc/bbc then it's gonna be 14mm threads...the seat design, thread reach, hex size, etc, may be different, but the threads are gonna be the same. If the 5671s don't fit, I'm betting the GR5s won't either...
As for the switchover from the gasket seat to tapered seat design, iirc it was in May...I'll have to check my notes to see exactly which week, but we have a set of 840s that share the 1.88 exhaust valve casting size but have the gasketed plug seat...and I've heard of 291s that are just the opposite.
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