C2 BB spark plugs

[Tom Merkel]

Gentlemen:

1. My shop manual for '67 427/425 states AC43N plugs. Can I assume it's the same for '66 427/425?

2. What does the "N" refer to?

3. Lastly, if AC43N's aren't available any longer for a '66 427/425, what would be a proven replacement plug?

Thanks.

Tom

[Clem Z.]

Re: C2 BB spark plugs

best plug for street driven BB corvettes is AC plug "R-45XLS"

[Dave S.]

Re: C2 BB spark plugs

The N is a Big Block plug. Clems R45 XLS suggestion is a good one. If you can't find those you could use an R45N or a 45N.

[Clem Z.]

Re: C2 BB spark plugs

the "N" means that the threaded end has threads only on the bottom half of the metal part the goes into the head. you cannot use "N" plugs in heads that are threaded all the way like big block aluminum heads. you can use plugs that are threaded all the length in heads for "N" plugs. i hope this is clear.

[Tom Merkel]

Re: C2 BB spark plugs

Clem - Thanks for the tip on BB plugs. I believe the 45XLS is an extended tip, versus the standard AC43/4/5 series.

Now, from personal experience on my '67 L-79, I (mistakenly) once put 45-XLS plugs in (extended tip), and it ran OK for about 100 mis. or so; then fouled, and sputtered.

Which gets me to wonder. From what you're saying, the '66 BB will perform OK with extended tip 45XLS for a typical street-driven machine. Yet, the '67 SB threw-the-bit using 45XLS. Curious situation.

Oh, I certainly believe your recommendation, and intend to drop a set in and see.

Thanks again.

Tom

[Clem Z.]

Re: C2 BB spark plugs

some small blocks because of the "dome" on the piston can hit the ground electrode so you must "index" the ground electrode to be located between 9-12-3 o'clock position when using a extended tip plug. XLS are extended tip plugs BUT they are also 3/4" reach and should NEVER be used in any small block chevy with cast iron heads which use a 3/8" reach plug

[Jeffrey S.]

Re: C2 BB spark plugs

Tom
The "N" in the 43N stands for the "reach" or length of the section that goes into the head. N means the reach is 3/4 of an inch, 3/8 of which is threaded.
I will contact you off line about where these are available.
Jeff Salz

[Clem Z.]

Re: C2 BB spark plugs

you can use #45 hotter plug to keep the fouling down and the extended tip allows the "fuel wash" to cool the plug at higher speed but at lower speed the extend tip hotter heat range will stay cleaner.

[Dave S.]

Re: C2 BB spark plugs

Clem,
I know the XLS style is used for an aluminum head application, but isn't an N style plug unique to a big block application???

[Clem Z.]

Re: C2 BB spark plugs

the "N" can only be used in BBC cast iron heads because they are only threaded the bottom 3/8" of the 3/4" reach of the plug. if they are installed in heads that are threaded all the way to the top you will either not be able to install the plugs all the the way into the heads or you could ruin the threads in the heads. this was not one of GM better ideas because i have seen BBC aluminum heads with the threads ruined because someone tried to install "N" type plugs.