Want to convert L72 from ported to full time Advance - NCRS Discussion Boards

Want to convert L72 from ported to full time Advance

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  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15667

    #16
    Re: Want to convert L72 from ported to full time Advance

    '68 OE L-71 with ported vacuum advance has a 15" 201 15 VAC. This will not pass the Two-Inch rule when you convert to full time. Typical L-78/72/71 idle behavior is 14" @ 900 with full time vacuum advance, and about 25 degrees total idle spark advance, so a 12" B26 is right on the money.

    What are are your engine's OE centrifugal advance specs. Check your CSM and AMA specs and post? Has it been modified from OE?

    What about the camshaft. Is it OE or bubba? You can get an idea by checking idle vacuum at 900. It should be at least 13" even with the ported vacuum advance and OE initial timing. If it's a lot less you have a bubba cam and need a different VAC.

    I can't say how many times someone has posted a question about setting up an OE engine spark advance, then ten posts later we find out the engine isn't anywhere near OE, and the biggest violation is usually a bubba cam with so much overlap that the engine won't idle anywhere near like OE and needs a completely different spark advance map setup than a real OE engine to run even half decent.

    Duke
    Last edited by Duke W.; March 3, 2014, 04:37 PM.

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    • Robert M.
      Frequent User
      • January 1, 1992
      • 78

      #17
      Re: Want to convert L72 from ported to full time Advance

      Hello Duke; the cam in my l-71 is to definitely to spec. not sure about the compression. The OE spec from the shop manual: 0 deg @ 900 rpm 30 deg @ 3800 the distributor part # 1111296 vacuum advance in crankshaft degrees 0 @ 8", 15 @ 15.5. I won't have a chance this week to verify the factory distributor specs as I will be out of town til next week.
      Bob

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      • Duke W.
        Beyond Control Poster
        • January 1, 1993
        • 15667

        #18
        Re: Want to convert L72 from ported to full time Advance

        Okay, check if the car meets spec. If it doesn't, post what it is when you get back. It might be best if you start a new thread since we're talking a different config. than L-72.

        Duke

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