Spark Plugs

[Gary Mancuso]

Hi guys, could you please tell me what is the prefered brand and heat range for a 67 427/435? As always thanks in advance

Gary

[Dave S.]

Re: Spark Plugs

Gary, The answer will depend on the way the car will be used. The purist owner will want AC 43N (3 heat range) as that was the plug that was used on the assembly line but I believe it is to cold for street use. Your next choice would be 44N (4 heat range) or the hotter 45N (5 heat range)which will be better for city driving. You could also use R44N or R45N which is the same heat range with the resistor feature. The resistor style should help the radio reception but with a 435 car you may not be able to hear the radio anyway. I happen to think the earlier 60's and 70's style AC plugs are a good choice but you will get likely get differing opinions on that. There is some good information on this in the archives.

[Gary Mancuso]

Re: Spark Plugs

Dave,

Appreciate the info. Can't imagine running AC43N's in this motor. Just took out a set of 44N's with approx. 500 mi. on them and they were totally fouled (fuel). I really think this motor needs an extended type electrode, at least in my motor. BTW the previous owner told me he had the motor rebuilt in the early eighties to factory spec and since then had been used sparingly, that is until I purchased it. As mentioned I was running an extended electrode and they appeared to be burning quite well. Only reason for the change was I had the AC's and was going to attend an all corvette judging event (TopVette) and wanted to play it safe if in fact they checked the plugs. Again, thanks for the info.

[Dave S.]

Re: Spark Plugs

Gary, Sounds like the 45N or 46N may be best. S is the letter for extended tip and I'm not familiar with NS N(big block) S(extended tip)plugs. The AC plugs are a requirement of flight judging.

[Daniel S.]

Re: Spark Plugs

Gary,

I have AC Rapid Fire #4's in my '68 L71 and they perform great.
Have approx 4000 miles on them with no problems.

I have a set of NOS AC 43N...but doubt I will even try them when the time comes to change plugs.

Dan

[Dan Grunwald]

Re: Spark Plugs

Dave,
Thanks for all of that info. I also have a 67 but it is running a 435 horse with alum heads from a 69. Any special thoughts on that or should I run the same plugs as a CI head. Daniel Grunwald

[Dave S.]

Re: Spark Plugs

I'm not knowledgeable about aluminun head cars but my common sense doesn't want me to think there is any real difference. Compression ratios and cam/valve configuration come into play and people more knowledgeable than I can chime in. I would guess the spark plug discussion would apply to both cast iron and aluminum heads in the same context. Hopefully the experts can add to this.