Spark plug advice

[dartfreak75]

Higher number, hotter plug with Champion plugs. NGK is the other way. The bigger number is colder.

I would do everything I could to use a a C series so you don’t have the dreaded 13/16 hex. And I’ll tell you why.

Because as much as I say use the C series, when I went into town Wednesday to grab some plugs and other junk to fire the 340 thats on my run in stand, and they only had N series plugs in the heat range I need.

The headers I’m using to fire this pig I’ve used since 1980, so I figured WTH they will be fine.

They go in there, but they are a PITA. I guess when I was younger it didn’t matter, but fighting that bigger socket just pisses me off.

That will be the LAST time I ever buy that dinosaur plug. If they don’t have the C series I’ll either order them, or if I need them in a hurry I’ll use Autolite’s or AC’s.

I now officially HATE the N series plugs to death.

Just an FYI.

I did some research and autolite also has a 5/8 version it's the 3924 and 3923 the they are two different heat ranges I believe the 23 is the colder.
What exactly does the heat range mean?

 

[yellow rose]

I did some research and autolite also has a 5/8 version it's the 3924 and 3923 the they are two different heat ranges I believe the 23 is the colder.
What exactly does the heat range mean?

Now that you’ve posted that, those are the AL numbers that cross to a 12 Champion with a 5/8 hex. Just remember that the cross reference is a close approximation, so if you have any brand of plug in the correct heat range and you switch brands and just go off the cross reference you may not get the heat range quite where it was.

Using the cross reference may (and most likely will) require some testing to get the heat range correct IF you already have it correct when you change brands.

Heat range (a rather loose term) is a measure of how much heat the plug pulls from the chamber and dumps into the cooling system. That’s why low output, low compression ratio engines take a hotter plug and vice versa. As the CR goes up, because you’ve created more heat, if you don’t use a colder plug, the plug overheats and will send the engine into detonation.

As an extreme example (because it’s easier to see with your eyes) take two plugs (I will use Champion numbers because I know them best) one being very “hot” (meaning it it will retain more heat in the plug) like a RC14YC and then compare it to a racing heat range plug, like say a C57CX and hold them side by each.

Look straight down from the ground wire on both plugs and pay attention to the porcelain and where it meets the shell.

On the 14 heat range plug you will see the porcelain doesn’t touch the shell until it’s close to the bottom of the shell.

Then look at where the porcelain on the top 57 heat range plug hits the shell. It will be almost at the top of the shell.

What you are look at is what controls the temperature the plug will operate at. The greater area of porcelain that is touching the shell, the COLDER the plug and of course, Vice versa.

The heat the plug “sees” during operation is controlled by how much of that porcelain is touching the shell, and then the shell dumps the heat of the plug into the cooling system through the threads.

Heat range is all about controlling the temperature the plug runs at during all the possible load/heat conditions the combustion chamber will see.

If the plug is too cold, it won’t have enough heat to burn any carbon deposits and such and it will foul.

And if the plug is too hot, the business end of the plug will be so hot it will cause detonation and that means death to any engine, but to any engine making big HP/CID it is catastrophic damage.

Also keep in mind that ALL a plug manufacturers have a different philosophy as to how to determine if the heat range is correct for any application.

IOW’s, each plug manufacturer has to determine how best to make the plug “readable” so the end user isn’t guessing what he range is correct. And they ALL do it differently.

The two best examples I have (because they are the two I’m most familiar with) is Champion and NGK.

When looking for correct heat range I first look at the shell of the plug. On a Champion plug, as a GENERAL rule you want the cad plating to be down to the top of the first thread. That’s a close start and then you can look at other things and see if you can finesse it another number one way or the other.

With an NGK, you want to be between 2 and 3 threads taking the plating off!! If you run an NGK with 1 thread of color gone it will be cold enough it will likely foul. And, if you’re not careful, you can start jacking more timing in the engine than it really needs to get the timing mark on the ground wore where it needs to be and then you get the dreaded detonation.

The opposite is true. If you use a Champion with 3 threads of heat in it, it will be glowing hot and detonation will start killing parts.

I hope this makes sense, but reading plugs is as much an art as it is a science and an experience. Read all you can on reading plugs, and then go test and start looking at them. Take notes and pictures before and after any change you make.

Pretty soon you’ll start to see trends in tuning that show up on the plugs.

And as a very wise man once wrote (he went by the name Shrinker on forums, and this is a paraphrase) “don’t get locked into a certain way of thinking when looking at plugs...never make assumptions...you can’t assume what you see is always the same between engines or even cylinders of the same engine” or something very close to that.

 

[dartfreak75]

Now that you’ve posted that, those are the AL numbers that cross to a 12 Champion with a 5/8 hex. Just remember that the cross reference is a close approximation, so if you have any brand of plug in the correct heat range and you switch brands and just go off the cross reference you may not get the heat range quite where it was.

Using the cross reference may (and most likely will) require some testing to get the heat range correct IF you already have it correct when you change brands.

Heat range (a rather loose term) is a measure of how much heat the plug pulls from the chamber and dumps into the cooling system. That’s why low output, low compression ratio engines take a hotter plug and vice versa. As the CR goes up, because you’ve created more heat, if you don’t use a colder plug, the plug overheats and will send the engine into detonation.

As an extreme example (because it’s easier to see with your eyes) take two plugs (I will use Champion numbers because I know them best) one being very “hot” (meaning it it will retain more heat in the plug) like a RC14YC and then compare it to a racing heat range plug, like say a C57CX and hold them side by each.

Look straight down from the ground wire on both plugs and pay attention to the porcelain and where it meets the shell.

On the 14 heat range plug you will see the porcelain doesn’t touch the shell until it’s close to the bottom of the shell.

Then look at where the porcelain on the top 57 heat range plug hits the shell. It will be almost at the top of the shell.

What you are look at is what controls the temperature the plug will operate at. The greater area of porcelain that is touching the shell, the COLDER the plug and of course, Vice versa.

The heat the plug “sees” during operation is controlled by how much of that porcelain is touching the shell, and then the shell dumps the heat of the plug into the cooling system through the threads.

Heat range is all about controlling the temperature the plug runs at during all the possible load/heat conditions the combustion chamber will see.

If the plug is too cold, it won’t have enough heat to burn any carbon deposits and such and it will foul.

And if the plug is too hot, the business end of the plug will be so hot it will cause detonation and that means death to any engine, but to any engine making big HP/CID it is catastrophic damage.

Also keep in mind that ALL a plug manufacturers have a different philosophy as to how to determine if the heat range is correct for any application.

IOW’s, each plug manufacturer has to determine how best to make the plug “readable” so the end user isn’t guessing what he range is correct. And they ALL do it differently.

The two best examples I have (because they are the two I’m most familiar with) is Champion and NGK.

When looking for correct heat range I first look at the shell of the plug. On a Champion plug, as a GENERAL rule you want the cad plating to be down to the top of the first thread. That’s a close start and then you can look at other things and see if you can finesse it another number one way or the other.

With an NGK, you want to be between 2 and 3 threads taking the plating off!! If you run an NGK with 1 thread of color gone it will be cold enough it will likely foul. And, if you’re not careful, you can start jacking more timing in the engine than it really needs to get the timing mark on the ground wore where it needs to be and then you get the dreaded detonation.

The opposite is true. If you use a Champion with 3 threads of heat in it, it will be glowing hot and detonation will start killing parts.

I hope this makes sense, but reading plugs is as much an art as it is a science and an experience. Read all you can on reading plugs, and then go test and start looking at them. Take notes and pictures before and after any change you make.

Pretty soon you’ll start to see trends in tuning that show up on the plugs.

And as a very wise man once wrote (he went by the name Shrinker on forums, and this is a paraphrase) “don’t get locked into a certain way of thinking when looking at plugs...never make assumptions...you can’t assume what you see is always the same between engines or even cylinders of the same engine” or something very close to that.

Thanks man that is some awesome info. I'm gonna get some of the rc12yc champions and try them. I also found some of the autolite 3923 which is supposed to be a step cooler that stock. All this is new to me I have never had to worry about performance stuff or detonation. Tbh back in the day I was proud If I could afford 8 matching plugs. Haha I use to scrounge up enough money to buy however many i could and a cap and rotor. And steal plug wires off another vehicle i parked and pull a few plugs from here or there and that was a tune up for me. Lol I may have 3 or 4 different brands and sizes and 3 or 4 different wires from random vehicles.