Spark plugs

[Rex T.]

Can someone tell me what the correct AC or Champion spark plug is for 1967
427-390 engine? Car has factory air and will be street driven. Thanks, Rex #8089.

[Dan Pepper]

Re: Spark plugs

Rex,

I've been using AC 43xls in my '66 390hp L36 with good results. The wise ones on the board recommend these plugs too since they have an extended tip. Apparently burns more efficiantly than the standard 43N plug suggested by GM.

[Rex T.]

Re: Spark plugs

Thanks Dan, that's what I needed to know since my engine has the "GM recommended" 43N's. Thanks for your help. Rex

[Jeffrey S.]

Re: Spark plugs

Rex
A 44N or even a 45N would also be a good choice. You just need a hotter plug for city driving. These would give you the higher heat range and also the exact reach that was designed for your car.
Jeff

[Clem Z.]

Re: Spark plugs

i would use a AC R 45 XLS because with the electrode closer to the center of the chamber the more effecient the burn. all new engines use the "fast burn" theory with the plug closer to the center of the chamber. with extended tip plugs you can even retared the timing a few degrees which may prevent knocking.

[Mike Cobine]

Re: Spark plugs - R43CXLS

While you are on the XLS plugs, can someone tell me what the R43CXLS plug is and whether or not it fits the big block?

Also, I thought the 43XLS had only been used in the aluminum heads since they have a deeper threaded section where the iron heads were farther down before they had threads and thus the 43N.

[Clem Z.]

Re: Spark plugs - R43CXLS

the C stands for copper, the core material used in the plug. i have heard that copper core plugs were invented by GM for the allison aircraft engines used durring WW2 but NGK made it big by using copper in its plugs and had a big advertising deal about copper core. the NGKs did work well in my old 2 stroke dirt bikes and snowmobiles. they had less tendency to foul out because they used a hotter tip design but the copper core pulled out the heat better.i think AC plugs still use a copper core in some if not all plugs but they quit using the C in the listing. yes a AC43CXLS will work in your BBC

[Duke W.]

Re: Spark plugs - R43CXLS

Yes, during the transistion phase to copper core plugs across the AC line, AC used a "C" in the suffix, but dropped it when the conversion was complete. That was some years ago. All modern "two dollar" spark plugs now have copper cores as far as I know, but, of course, they still have nickel alloy electrodes as copper would not last very long in the combustion chamber environment.

Duke