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1965 2door HT Helena, GA 31037
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Discussion Starter · #1 ·
I have finally got a rebuild started on my engine and need some advice on spark plugs. I will be using Dart 127121 64cc Aluminum Heads with 180cc runners, 357 bore, Edelbrock C3BX intake with 180cc runners, Edelbrock 1406- 600cfm Carburetor, CompCams XE262H camshaft, 9.25:1 compression and a Pertronix D7104600 ignitor III system with Pertronix 708101 spiral wound wires.

The Summit website suggested a list of spark plugs which were NGK 2669, 5238 and Autolite R3933 with all being 14mm X 0.750” for the Dart heads so it appears that is the size plugs I will be needing.

Also, since I’ll be using the Pertronix system with spiral wound wires, I have read that I will need to use non-resistor spark plugs. Can anyone verify this info?

So, here is what I need info about. What plugs do I need to purchase to get the right heat range and will
I need to use non-resistor plugs with the wires I will be using. I know nothing about spark plugs and any info you can give me will be appreciated.
 

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Mike - 74 Nova Baltimore, MD
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I can't help you with the heat range, but I run resistor spark plugs with my spiral core wires.
I run the Autolite 3924 resistor spark plugs (14mm / Gasket / .750 Reach) in my 10:1 400 sbc with AFR 195 heads... and these plugs have been working great for me.
 

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1965 2door HT Helena, GA 31037
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Discussion Starter · #8 · (Edited)
Andy, I should have known you'd get me on that one. 😄 I'm thinking that a "Sniper" is a whole lot more than I'll need
on my engine so I'll stick with my 600 CFM 1406.

Automotive tire Product Motor vehicle Font Toy


OK, on the AutoLite plugs. There was something that I failed to include in my info and it was the plugs that I need
would need to have a 0.750 reach with a Gasket Seat for the Dart Heads. This came from the JEGS website in their
specs. for the Dart Heads.

Also, something that I notice is that both of these plugs have 1.25 threads with 0.750 reach. Why would the threads
be longer than the reach? I don't understand this part.

3924 - Spark Plug, Iridium XP Enhanced Alloy, Resistor, 14mm x 1.25 threads, Gasket Seat, 0.750 in, Reach.
3926 - Spark Plug, Copper Core, Resistor, 14mm x 1.25 threads, Gasket Seat, 0.750 in, Reach.

After spending today reading up on spark plug heat ranges, it seems this is something that I'm going to have to zero
in on after I get the timing set and the engine running for a while. Is this correct? This is getting beyond me since
I've only been used to going to the parts store and saying " Gimme some plugs for my '79 Chevy 350ci"!!

Then adding on the multi-sparking ignition system and more things come into the equation.
Sam
 

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Andy, I should have known you'd get me on that one. 😄 I'm thinking that a "Sniper" is a whole lot more than I'll need
on my engine so I'll stick with my 600 CFM 1406.

View attachment 428695

OK, on the AutoLite plugs. There was something that I failed to include in my info and it was the plugs that I need
would need to have a 0.750 reach with a Gasket Seat for the Dart Heads. This came from the JEGS website in their
specs. for the Dart Heads. It appears the 3924 plugs have a tapered seat so I can't use them.

Also, something that I notice is that both of these plugs have 1.25 threads with 0.750 reach. Why would the threads
be longer than the reach? I don't understand this part.

(X) 3924 - Spark Plug, Iridium XP Enhanced Alloy, Resistor, 14mm x 1.25 threads, Tapered Seat, 0.750 in, Reach.

I like the idea of the Iridium plugs for longevity, but would need them with a Gasket seat.

3926 - Spark Plug, Copper Core, Resistor, 14mm x 1.25 threads, Gasket Seat, 0.750 in, Reach.

After spending today reading up on spark plug heat ranges, it seems this is something that I'm going to have to zero
in on after I get the timing set and the engine running for a while. Is this correct? This is getting beyond me since
I've only been used to going to the parts store and saying " Gimme some plugs for my '79 Chevy 350ci"!!

Then adding on the multi-sparking ignition system and more things come into the equation.
Sam
I would call Dart and ask them what their recommendation is directly. They build these heads for purpose, and with that said, should know what plugs work best with different applications including all heat ranges and combinations. That's how they test them for quench, swirl, etc. Just a thought...

Here's their info:

Main Line: 248-362-1188
 

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1965 2door HT Helena, GA 31037
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Discussion Starter · #10 ·
We are thinking along the same line. I was sitting here thinking that maybe I should do exactly what you suggest.
I'll give them a call tomorrow and post back about what I found out. It's tough being from the "Old School" and trying
to figure out what I need in a "New School" environment. Thanks for helping me.
Sam
 

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We are thinking along the same line. I was sitting here thinking that maybe I should do exactly what you suggest.
I'll give them a call tomorrow and post back about what I found out. It's tough being from the "Old School" and trying
to figure out what I need in a "New School" environment. Thanks for helping me.
Sam
We're all in this together!! I'll row a bit, then you can row a bit, then we all can row a bit together. We'll get there eventually... Wherever "there" is :p I'm planning on a long dirt nap at some point... Nice and quiet.
 

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Mike - 74 Nova Baltimore, MD
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Also, something that I notice is that both of these plugs have 1.25 threads with 0.750 reach. Why would the threads
be longer than the reach? I don't understand this part.
The 1.25 number is not the length of the threads... it is the pitch of the threads.
Both the Autolite 3924 and 3926 would fit in your Dart aluminum head.... as they are both 14mm gasket plugs with .750 reach.

Anyway, keep us posted on what Dart recommends for your engine.
 

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Yeah, the metric thread is 14mm diameter x 1.25 threads per millimeter pitch.

Like SAE 3/8"-16 tpi is 3/8" diameter x 16 threads per inch.

So for 14mm x 1.25 with .750 reach(19mm) that would work out to 15.25 threads on that .750" length.
 

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1965 2door HT Helena, GA 31037
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Discussion Starter · #14 · (Edited)
About the threads. Thanks for the info. Now I understand what that is all about. I certainly didn't have a
clue about what the 1.25 meant. Now I'm educated! Another question. Is the 1.25 sorta like a standard
thread or are there a lot of different threads used in the industry for production automobiles? Just curious.

Ok, here is what I found out from Dart. The guy I talked to said Dart does not offer any advice about spark
plugs because there are so many different heat ranges and materials made by different companies. He did
say that they do like Autolite. He told me there was an info sheet inside the box with the heads that had
some info. I did see some papers inside the boxes but didn't read any of it before taking the heads to the
machine shop. DUH!

I gave the guy at Dart the part number of my heads and asked if he could confirm the plugs as being
14mm X .750" and he said yes that was it. So the plugs Summit recommended will fit the heads correctly
but are listed as "Racing" plugs, which I don't need.

After some thought today, I think I'll purchase a set of Autolite-3924 to start off with and see how they'll work.

I'm going to be running my original Rams Horn manifolds and you guys know how hard it is to get to the
plugs using those things so changing the plugs often is going to be a chore. Maybe after the second or so
scheduled inspections of the plugs, I may give a set of Iridium NGK plugs a try for more longevity. Does
this sound like a plan that could be workable?

Andy, I know what you mean about the nap....I'm 74 and slowing down tremendously. :sleep:

Happy Thanksgiving to you all and I wish you well.
Sam
 

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Sam, sounds like a good plan. The ram's horn manifolds will definitely pose some issues but not as much as some of the headers we've seen... You can always go up or down with the heat range and with your combo, you're probably close if not right on the money with those 24s. When you do change to the iridiums, check with these guys here and see what a comparable plug would be to whatever you end up landing on... range, reach, etc. I only have them in my newer cars so not much experience with them and gapping to work with an aftermarket ignition I have heard can be a chore but, I'm sure others here have experience and will be happy to share.

As for 74... Spring Chicken!! The pine box can friggin' wait! You have things to do and tires to wear out!!! :p

Wishing you and yours a safe and happy holiday, however you celebrate :)

~Andy
 

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Mike - 74 Nova Baltimore, MD
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Is the 1.25 sorta like a standard thread?... or are there a lot of different threads used in the industry for production automobiles?
I'm not really sure about all of the metric variations... but the 14mm x 1.25 seams to be a very common size for spark plugs.
 

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The beauty of the more exotic spark plugs is the wide heat range. I suspect you could simply use a cross reference to the 24s and be well within the proper heat range.
Are the iridiums that much more tolerant of variation? I guess I really need to do more research on them and get to know them better. Sounds like they may offer a lot more bang for the buck for boosted motors too... Possibly...
 

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1965 2door HT Helena, GA 31037
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Discussion Starter · #20 ·
Since I'll be using the Pertronix multi-spark system it appears that standard copper plugs would be more
susceptible to a deterioration of the electrode. Since iridium is a harder material all I've read about them
says they will last longer but cost more. The cost isn't that much of a deterrent to me but the longevity would
be an advantage because of less physical labor that would be involved having to change plugs less often.
Of course, I'll not be driving my Nova as many miles as I would have back in the '60s but it sure would be
nice to install the plugs and not have to worry about another change for many, many miles.

I'll be picking up the 3924 plugs tomorrow and go with them first. Thanks for the help guys.
Sam
 
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