1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

[Rob A.]

I'm considering having my survivor 1967 427 / 435 HP convertible judged this year. One of the items on my list to address is the spark plugs. The correct plug is the AC43N which I can find but they are fairly costly. Does the AC R43N work as well as the AC 43N? My understanding is that the R is a resistor plug.

I'd appreciate any input on which plugs to use that make the car perform well and pass Judging criteria.

Thanks,
Rob

[Gene M.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

If you don't have the original plugs in the engine that it came with then in bow tie judging it don't matter what's in there'

[Ara G.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

Rob,
Regarding plugs, some judges (myself included) try to look closely at the plugs and see if the plug is an R43N or a 43N. Full credit needs to given to the folks who have correct plugs. Without touching the boot, we can sometimes see the part numbers on the plug, thus 43N's are the way to go. This applies to Flight judging obviously. Regards. ARA

[Rob A.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

Thanks for the replies. A couple more detailed questions, does the L71 perform well with the 43N plugs (I am using Sunoco racing fuel)? I've read that using resistor plugs (R43N, R45N, etc.) can damage the coil and TI unit, is that true?

[Joe L.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

Thanks for the replies. A couple more detailed questions, does the L71 perform well with the 43N plugs (I am using Sunoco racing fuel)? I've read that using resistor plugs (R43N, R45N, etc.) can damage the coil and TI unit, is that true?

Rob------

GM replaced virtually all of the non-resistor plugs with resistor type. So, apparently, they think that resistor plugs can be used in place of non-resistor with no problems. As far resistor plugs causing damage to the coil and TI unit, I'd say that's some kind of "old wive's tale". 1969 Corvettes were the first ones to use resistor plugs and they used, essentially, the same coil and TI amplifier as earlier.

Will 43N spark plugs run well in an L-71? They'll run just as well as they ever did.

[Duke W.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

Thanks for the replies. A couple more detailed questions, does the L71 perform well with the 43N plugs (I am using Sunoco racing fuel)? I've read that using resistor plugs (R43N, R45N, etc.) can damage the coil and TI unit, is that true?

AC heat range "3" is too cold for normal street and highway driving. If you plan on driving the car the hotter heat range "5" is a better choice to prevent fouling, and the currently available R45XLS is what most guys run in early big blocks.

[Joe L.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

AC heat range "3" is too cold for normal street and highway driving. If you plan on driving the car the hotter heat range "5" is a better choice to prevent fouling, and the currently available R45XLS is what most guys run in early big blocks.

Duke------


Yes, I would recommend the R45XLS or equivalent, too. However, it sounded to me like one of Rob's criteria was originality/judging. For that, he'd need to find some NOS 43N. I wouldn't recommend using these plugs from a functionality perspective but if they are used they'll work as well as they ever did (which, of course, is not necessarily all that good for street operation).

[Rob A.]

Re: 1967 L71 427 / 435 Correct Spark Plugs - Performance and Judging

Thanks everyone for the input. I guess there is not a plug that does both, meet the judging requirements and perform well. I ended up buying two sets of plugs, 43N and 45N. I will use the 45N for driving and enjoying the car. And use the 43N for judging so ARA won't ding me...(joking).

It is strange that Chevrolet recommended a plug that was too cold for the L71. I guess they wanted to insure their dealers had something to service on these cars...