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Old 05-22-2022, 04:18 PM   #141
Tim Ayers
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Default Re: Spark Plug Protrusion into Head?

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In NGKs, I don't like to run a heat range of '4' (a bit too hot for me) - much prefer a '6' for a performance street engine. NGK has a whole host of .750 reach plugs - with various electrode designs, heat ranges, different materials/cores, etc. You might checkout the NGK 7910 - which is a heat range of 6. Another number that I used to use is a B6ES . . . which can be cross-referenced to a lot of different plugs.

Another option is a R5671A-7 - which is a racing plug, but it is in a heat range of '7' - which is a bit cooler - though their racing plugs don't come much hotter than this (for obvious reasons).

Keep in mind the nomenclature for NGK is backwards from Champion (when it comes to heat range). The lower the number, the hotter for NGK.

Thanks, Dale. I've got .750" extended reach 4's & 6's coming in. I'll start with the 6's and see how they do.
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Old 05-22-2022, 08:04 PM   #142
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Default Re: Spark Plug Protrusion into Head?

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No, repop Cyclones. The hole depth is +/-.625". I tired to post a pict, but the file was too large. I have a set of new block letter Edlebrocks on the shelf in case I need to swap.

For a number of reasons, I would not have used these Cyclones if I was to do it again. They have some porous areas and are weeping at the two casting nubs on each head. I'm going to run some silicon silicate to hopefully stop those weeps coming from the casting nubs.

I wanted pre-war heads and these were originally made just before the war.
Yeah, there were not many heads made before WWII. I have a set of Eddie Meyers, but I just didn't want to work the Hell out of the combustion chambers to handle the big-ass cam that I'm running . . . so I put a set of my Navarro's on instead (not pre-war). Sometimes one has to compromise!
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Old 05-22-2022, 08:27 PM   #143
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Default Re: Spark Plug Protrusion into Head?

Finding the right spark plugs for a new engine combination can be time consuming and a bit costly but it needs to be absolutely right if the engine is to run up to it's capability.
Before anything, they have to be the correct reach. That means the plug should have the same reach as the threads in the head minus the washer thickness so when installed there are no threads showing either on the plug or the head and the electrodes should not be exposed so much as to be touched by the valves or the piston in the case of an OHV engine.
If in a preliminary test the plug is short of the head surface,
you will need a longer reach plug.
If the plug threads go past the head surface, you either need a shorter reach plug or a SOLID copper washer of correct thickness.
The washer that comes with the plug usually is a compression type and is adequate for stock applications only.
If you want a bit more than stock, solid copper washers will give a closer "reading" and work better longer. It has to do with heat transfer. A plug is designed to be installed with all of the threads in contact with the head so stacking washers is not recommended. Most of the heat transfer is through the washer seat, not the threads.
In some cases if the correct reach plug is not available, one thread in the head can be chamfered away so it doesn't show.

After the engine is installed and running it can be driven as it is intended to be and the correct heat range can be determined. This is the expensive part of the project. Sometimes it takes 2 or 3 sets of plugs to find what is correct.
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Old 05-22-2022, 10:25 PM   #144
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Default Re: Spark Plug Protrusion into Head?

Would there be a problem using a plug without the gasket? If you have a head that requires a 5/8" plug, removing the gasket from a 1/2" reach plug should just about make it correct.
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Old 05-22-2022, 10:32 PM   #145
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Default Re: Spark Plug Protrusion into Head?

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Would there be a problem using a plug without the gasket? If you have a head that requires a 5/8" plug, removing the gasket from a 1/2" reach plug should just about make it correct.
I would not run it without a gasket. There would be a good chance of galling the seat, especially on an aluminum head.
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Old 05-22-2022, 10:51 PM   #146
Tim Ayers
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Default Re: Spark Plug Protrusion into Head?

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Just ordered an index tool, a set of various thickness copper washers and those ARP .120" washers. Hoping this will help me find the correct washer needed.

Thanks all of the replies.
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Old 05-23-2022, 01:01 AM   #147
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Default Re: Spark Plug Protrusion into Head?

Good luck Tim, you'll figure it out!
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Old 05-23-2022, 06:51 AM   #148
Tim Ayers
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Default Re: Spark Plug Protrusion into Head?

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Yeah, there were not many heads made before WWII. I have a set of Eddie Meyers, but I just didn't want to work the Hell out of the combustion chambers to handle the big-ass cam that I'm running . . . so I put a set of my Navarro's on instead (not pre-war). Sometimes one has to compromise!
I hear you. If these don't work, I've got Navarro's and Edelbrock's to choose from.
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Old 05-23-2022, 07:27 AM   #149
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Default Re: Spark Plug Protrusion into Head?

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Good luck Tim, you'll figure it out!
Thanks, Dale. Like Ronnie says, "It's all part of back yard hot rodding!"
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