1963 spark plugs
I am replacing the spark plugs in my '63 327 ci, 340 hp solid lifter convertible. I need help choosing the right plugs. The car currently has an "R45S" plug. the NCRS judging manual state "AC44" plugs. Mid America recommends "R43" and Paragon recommends "R45." Any advice as to what plug I should use will be most appreciated. I am also confused about what 1) the difference between 43, 44, & 45, 2) what the "S" suffix means and 3) why some AC plugs are 'green stripe."
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Re: 1963 spark plugs
For both highway and city use the consensus is a heat range 5. The AC R45S plug meets that spec. As far as the S designation that means the porcelain of the plug extends further down which helps in preventing fouling . AC 44 plugs were originally installed at the factory but they are too cold for overall street use. -
Re: 1963 spark plugs
See post #6 in the 2014 thread you posted to this morning.
https://www.forums.ncrs.org/showthre...7-340-Corvette
AC plugs with a "S" suffix means an extended tip. They are theoretically more resistant to fouling and slightly raise the compression ratio. On a SHP/FI engine with domed pistons significant block deck and head surface machining may allow the ground electrodes to contact the pistons.
If you don't want to take a minor deduction you'll have to find a set of NOS AC 44 plugs that have the proper artwork, which changed over the years. If you're not concerned with a minor deduction use the AC R45. I'm not sure what the "green strip" AC plugs are you refer to. Most AC plugs have green strips on the insulator, but as I previously said the artwork changed slightly over the years.
If you're not concerned about judging use the Denso or NGK plugs recommended in the above referenced thread, both of which are non-resistor equivalents to the out-of-production AC 45.
DukeComment
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Re: 1963 spark plugs
Thanks for the info!Comment
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