1970 spark plug gapping - NCRS Discussion Boards

1970 spark plug gapping

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  • D S.
    Extremely Frequent Poster
    • March 1, 2005
    • 1551

    1970 spark plug gapping

    I gave up on the archives to find out this information. Mine is a stock 1970 454/390, if that matters. I have R45Ts to install. Is the gapping .035 or .040 or .045?

    Thanks,
    Scott Sims
    Texas Chapter
  • Michael D.
    Expired
    • June 30, 1996
    • 536

    #2
    Re: 1970 spark plug gapping

    .035. If memory serves, it's printed on your tune up sticker.

    Comment

    • Pat M.
      Extremely Frequent Poster
      • April 1, 2006
      • 1575

      #3
      Re: 1970 spark plug gapping

      I think it's also in the service manual.

      Comment

      • Ken P.
        Expired
        • April 1, 1990
        • 77

        #4
        Re: 1970 spark plug gapping

        Lots of information here:

        GM Heritage is committed to preserving the rich history of General Motors brands while providing a foundation for continued innovation into the future.

        Comment

        • Joe L.
          Beyond Control Poster
          • February 1, 1988
          • 43218

          #5
          Re: 1970 spark plug gapping

          All-----


          The only spark plug gap that anyone with a 1953-74 Corvette has to know is 0.035". ALL 1953-74 Corvettes specified this gap.
          In Appreciation of John Hinckley

          Comment

          • Joe C.
            Expired
            • August 31, 1999
            • 4598

            #6
            Re: 1970 spark plug gapping

            The reason for larger gaps was because HEI enabled it beginning in 1975. As stated, anything prior to that used low voltage coils which would only allow gaps as large as .035".

            Comment

            • William F.
              Extremely Frequent Poster
              • June 9, 2009
              • 1363

              #7
              Re: 1970 spark plug gapping

              Looked up specs for AC "Rapid Fire" plugs on AC web site and they recommend a .040 gap for use in earlier(non taper thread) big blocks such as my '67 L36. I have non transistor ignition, standard coil, etc. Would .040 or .035 be best in this case?

              Comment

              • Michael W.
                Expired
                • April 1, 1997
                • 4290

                #8
                Re: 1970 spark plug gapping

                I'll bet you .005" that it will make no difference.

                Comment

                • Joe C.
                  Expired
                  • August 31, 1999
                  • 4598

                  #9
                  Re: 1970 spark plug gapping

                  Originally posted by Michael Ward (29001)
                  I'll bet you .005" that it will make no difference.
                  Mike,

                  I've been meaning to ask you this for awhile. I heard that you knew the answer to this: Why did racers back in the day like to "short gap" their spark plugs?

                  Comment

                  • D S.
                    Extremely Frequent Poster
                    • March 1, 2005
                    • 1551

                    #10
                    Re: 1970 spark plug gapping

                    Originally posted by Joe Lucia (12484)
                    All-----


                    The only spark plug gap that anyone with a 1953-74 Corvette has to know is 0.035". ALL 1953-74 Corvettes specified this gap.
                    Thanks, Joe! Now that I have five new spark plugs installed tell me the tricks to 1.) get the plug boots to release from the old spark plugs. 2.) get to the three spark plugs on the passenger side behind the AC compressor and dipstick tube brace. I've got the car jacked up in hopes it will be easier from the bottom side. You small block owners are lucky.

                    Comment

                    • D S.
                      Extremely Frequent Poster
                      • March 1, 2005
                      • 1551

                      #11
                      Re: 1970 spark plug gapping

                      Originally posted by Ken Preston (17054)
                      Ken, thanks for this! Saved it as a Favorite. I couldn't find a service tag and I have a 1968-1072 Corvette repair manual that I could not find the answer there.

                      Comment

                      • Michael W.
                        Expired
                        • April 1, 1997
                        • 4290

                        #12
                        Re: 1970 spark plug gapping

                        Originally posted by Joe Ciaravino (32899)
                        Mike,

                        I've been meaning to ask you this for awhile. I heard that you knew the answer to this: Why did racers back in the day like to "short gap" their spark plugs?
                        To get to the other side? Dunno, ask Clem, he's old.

                        Comment

                        • Thomas H.
                          Extremely Frequent Poster
                          • August 31, 2005
                          • 1058

                          #13
                          Re: 1970 spark plug gapping

                          I don't have AC on my LS5, but I would venture that cars, such as yours, with AC are easier to get at from the underside.

                          I have power breaks and cylinders 5 and 7 cause me to do some contortions to get at them.

                          Tom
                          1958, 283/245, White/red - Top Flight, October 2016
                          1960, Black/black, 283/230 4sp
                          1966, Black/Red, 327/350 4sp w/AC
                          1967, 427/390, 4sp, Goodwood Green, Coupe
                          1971 LS5, 4sp, coupe, Bridgehampton Blue
                          2007 Z06, Lemans Blue

                          Newsletter Editor, Delaware Valley Chapter

                          Comment

                          • Joe C.
                            Expired
                            • August 31, 1999
                            • 4598

                            #14
                            Re: 1970 spark plug gapping

                            Originally posted by Michael Ward (29001)
                            To get to the other side? Dunno, ask Clem, he's old.


                            I already know the answer. I'd like to know if you do as well. Apparently, according to your post #8, you don't believe that widening the gap will make any difference. I disagree. The question is designed to determine if you feel the same way about smaller gaps as well.

                            When it comes to ignition systems, you remind me of Mr. Williams. You're both stranded in the year 1972, although his arrested development applies to all aspects of engine technology. His dissertations on camshafts, especially, are not always supported by thorough analysis.

                            Comment

                            • William C.
                              NCRS Past President
                              • May 31, 1975
                              • 6037

                              #15
                              Re: 1970 spark plug gapping

                              Remember we are talking about 1970 technology, and a high compression engine, the ignition system can get a little marginal at high rpms. The stock class racers commonly closed down the gaps to ease the voltage requirement for high rpm operation. This was done in conjunction with other tips of the trade all aimed a maximizing the likleyhood that the mixture would get lit under a max performance situation. HEI and other modern ignition systems pretty much eliminated the problem, although not without other issues, so it's relavent to a question of "in the day"
                              Bill Clupper #618

                              Comment

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