[Goatracer1]

If I'm not mistaken the NGK numbers you are listing are all Iridium plugs. How about listing the copper and platinum numbers also.

[Formulajones]

The plugs I've listed like the UR5 and XR5 are the copper plugs.

The long reach like the BKR5E are also the copper plugs.

They are what NGK refers to as their nickel plugs, which are copper core with a nickel coating.

[Scott65]

For my part, I'm gonna try to stick to the BKR"X"E plugs. There are some other variations, but some of them vary more than material. Like the aforementioned change of hex size that would render them useless on the Edelbrocks. This will be a work in progress for a bit as the verification is more difficult than I envisioned.

[Goatracer1]

Sorry, the numbers that I had found for copper plugs were 2 letters and a number or 4 numbers. I guess their system is just too confusing for me.

[johnta1]

Here is a chart that I usually use, not sure how current it is.
It doesn't explain the R5671 type plugs though, haven't found anything on decoding them.

The lower section has the iridium etc decode.

[johnta1]

Here's a link to another chart

Dragstuff sparkplug chart

[Formulajones]

Originally Posted by johnta1

Here is a chart that I usually use, not sure how current it is.
It doesn't explain the R5671 type plugs though, haven't found anything on decoding them.

The lower section has the iridium etc decode.

Yeah I've never been able to decipher that plug other than possibly the heat range and that's about it. Dad's been running them for years and I believe it's a fairly cool 7 heat range, and I know it's not an extended reach electrode just by looking at it, it's down inside the plug which I've never considered optimal. In fact we always used to refer to them as "oil burnin' plugs" LOL Because the electrode is down inside the plug and shrouded from oil in the burn process

NGK's number system has always been confusing, one of the reasons they aren't my favorite, but I use them in certain engines anyway. All I really care about is that I stick to basic copper core, with the right thread pitch and length (gasket or not) and that it has the extended tip electrode. From there I just want a certain heat range and I'm good to go.

[Formulajones]

Originally Posted by johnta1

Here's a link to another chart

Dragstuff sparkplug chart

Just a tip on those Autolite plugs listed. If you take the "R" out of the part number it's just your basic Autolite copper core plug in that particular style and heat range.

I've had them both in my hand and the only difference I can visually decipher from the 2 are the fact that the race plugs have the ground strap cut back slightly so it's just barely over the electrode. At least that's how they used to be.

I've been doing that mod to the regular plugs for years with a small dremel and steady hands for anyone interested in making a similar plug from the standard lineup.


Side note: Isn't it funny how NGK keeps using that 6 heat range to cover multiple heat ranges offered by other plugs.
The AR23 and 24 for example. I see this in various charts.
So the colder heat ranges are available in Autolites but to get to them in the NGK you have to step over to the NGK racing plugs, which I don't believe are resistor plugs. Another reason why I sometimes prefer the Autolites over the NGK's.

[Scott65]

You can get to a 7 in the projected tip design. BKR7E(-XX)

[Formulajones]

Originally Posted by Scott65

You can get to a 7 in the projected tip design. BKR7E(-XX)

Yep I think we're good when talking about the 3/4" reach plugs for aluminum heads.

Where I run into problems for example, are when I want a 13/16 plug for pre 71 iron heads in an XR6. Coldest they have that I've ever found is a 5 in that style plug so I usually switch over to Autolite for that application, they have more selections.

[Scott65]

Maybe they've conceded a certain segment... I was thinking for your Dads the may allow a projected tip that works well if he's N/A. 7 could get iffy with power adders pretty quick.

[Formulajones]

Originally Posted by Scott65

Maybe they've conceded a certain segment... I was thinking for your Dads the may allow a projected tip that works well if he's N/A. 7 could get iffy with power adders pretty quick.

Yeah he's N/A

Wouldn't 7 be a pretty cold plug? I think comparable to a 3922 autolite which I believe is about as cold as they get in Autolite for that style.

I was thinking of trying a BRK6E in it, which isn't a hot plug either, although not against the 7 since that's what he's had in it.

The 6 heat range for NGK seems to follow along the lines of, for instance, the R43 AC plugs for those that understand the AC plugs better. A "5" in NGK would be more along the lines of a R44 AC, a very common middle ground heat range in my opinion.

So if everyone considers the R43 plugs to be a cold plug, then I tend to believe we would think that way about the "6" heat range in the NGK line.

I'm just trying to see if I can put this in really simple terms that we all understand.

Unless you are seeing charts that are way off of this?

[Scott65]

I've seen it referenced both ways in regards to heat range... I chose the 6 for mine as an experiment to one heat range colder than the 3924 Autolite. It seems roughly correct for that. Heat mark about halfway down the strap anyways. FWIW

[Formulajones]

Originally Posted by Scott65

I've seen it referenced both ways in regards to heat range... I chose the 6 for mine as an experiment to one heat range colder than the 3924 Autolite. It seems roughly correct for that. Heat mark about halfway down the strap anyways. FWIW

Yep I think we're on the same page. That's how I view it too, the 6 is one heat range colder than a 3924.

I see the 3923 and the "6" NGK as the same heat range or very close.