L48 1.6 ratio rocker arms, carburetor adjustment - NCRS Discussion Boards

L48 1.6 ratio rocker arms, carburetor adjustment

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  • Dan L.
    Expired
    • November 8, 2010
    • 27

    L48 1.6 ratio rocker arms, carburetor adjustment

    I recently changed the valve stem seals on my 78 stock L48 engine. While I was at it I installed a set of 1.6 ratio roller rocker arms. I believe the original stamp steel rockers were 1.5 ratio. The question I have is will the higher ratio arms effect carburetor adjustment? I haven't got the engine back together yet and would like to know what to expect.

    Thanks

    Dan Leslie
  • Clem Z.
    Expired
    • January 1, 2006
    • 9427

    #2
    Re: L48 1.6 ratio rocker arms, carburetor adjustment

    Originally posted by Dan Leslie (52432)
    I recently changed the valve stem seals on my 78 stock L48 engine. While I was at it I installed a set of 1.6 ratio roller rocker arms. I believe the original stamp steel rockers were 1.5 ratio. The question I have is will the higher ratio arms effect carburetor adjustment? I haven't got the engine back together yet and would like to know what to expect.

    Thanks

    Dan Leslie
    if your engine uses the "double D" push rod guide hole make sure the push rod is not bottoming out on the guide hole at full lift. this is a problem because the push rod cup in the rocker is closer to the pivot point causing it to be closer to the bottom of the "double D" hole. most of the time you meed a fixture called a "louis tool" to lengthen the push rod guide hole. http://www.jegs.com/i/Comp-Cams/249/...oductId=747132

    Comment

    • Duke W.
      Beyond Control Poster
      • January 1, 1993
      • 15678

      #3
      Re: L48 1.6 ratio rocker arms, carburetor adjustment

      My recommendation is to reinstall the OE rockers and put the aftermarket hot rod parts on ebay.

      It's a single catalyst L-48. It's got over 10 psi exhaust backpressure at 5000!

      Until you do something about the very high exhaust backpressure, any internal mods are worthless, and so-called "1.6 rockers" are marginal even with open exhaust, and the lifters will pump up sooner.

      It's all marketing hype.

      Duke

      Comment

      • Joe L.
        Beyond Control Poster
        • February 1, 1988
        • 43221

        #4
        Re: L48 1.6 ratio rocker arms, carburetor adjustment

        Originally posted by Duke Williams (22045)
        My recommendation is to reinstall the OE rockers and put the aftermarket hot rod parts on ebay.

        It's a single catalyst L-48. It's got over 10 psi exhaust backpressure at 5000!

        Until you do something about the very high exhaust backpressure, any internal mods are worthless, and so-called "1.6 rockers" are marginal even with open exhaust, and the lifters will pump up sooner.

        It's all marketing hype.

        Duke
        Dan and Duke-----


        I agree. I would not consider the use of 1.6:1 rockers on a small block.
        In Appreciation of John Hinckley

        Comment

        • Michael M.
          Very Frequent User
          • February 1, 1993
          • 604

          #5
          Re: L48 1.6 ratio rocker arms, carburetor adjustment

          Duke and Joe, can you explain a little more on what you mean about not using 1.6:1 rocker arms on a small block. I always felt more power and my dyno tests showed better performance with the 1.6:1 ratio on the small block.

          Comment

          • Joe L.
            Beyond Control Poster
            • February 1, 1988
            • 43221

            #6
            Re: L48 1.6 ratio rocker arms, carburetor adjustment

            Originally posted by Michael Mytro (22211)
            Duke and Joe, can you explain a little more on what you mean about not using 1.6:1 rocker arms on a small block. I always felt more power and my dyno tests showed better performance with the 1.6:1 ratio on the small block.

            Michael------


            While the 1.6 rockers might produce a little more power, it comes at the expense of other things like valve train durability, etc. The small block valve train was designed around 1.5:1 rocker ratio. GM only made one small block ever with 1.6:1 rockers and that was the 1996 LT4. However, the rest of that valve train was designed with this in mind.

            Using the 1.6:1 rockers is, basically, an easy way to achieve additional valve lift but it's not the right way to do it. The right way is to install a camshaft with additional lift.
            In Appreciation of John Hinckley

            Comment

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

              #7
              Re: L48 1.6 ratio rocker arms, carburetor adjustment

              Originally posted by Dan Leslie (52432)
              I recently changed the valve stem seals on my 78 stock L48 engine. While I was at it I installed a set of 1.6 ratio roller rocker arms. I believe the original stamp steel rockers were 1.5 ratio. The question I have is will the higher ratio arms effect carburetor adjustment? I haven't got the engine back together yet and would like to know what to expect.

              Thanks

              Dan Leslie
              The faster and higher lift will not effect your actual overlap, which is based purely on the dwell time that both intake and exhaust valves are open simultaneously at "advertised", "seat-to-seat', or SAE J604D duration. What it will affect is the engine's effective overlap because there is more inch-degree area during that same dwell period since the valves are being lifted/lowered off of/on to their seats faster than with the original, nominal 1.5:1 ratio (1.37:1 actual) rocker arms.

              This will cause a lowering of engine vacuum at all RPM ranges. It will be most noticeable at idle, and will require you to adjust the curb idle screw to compensate.

              Comment

              • Joe R.
                Extremely Frequent Poster
                • May 31, 2006
                • 1822

                #8
                Re: L48 1.6 ratio rocker arms, carburetor adjustment

                Originally posted by Dan Leslie (52432)
                I recently changed the valve stem seals on my 78 stock L48 engine. While I was at it I installed a set of 1.6 ratio roller rocker arms. I believe the original stamp steel rockers were 1.5 ratio. The question I have is will the higher ratio arms effect carburetor adjustment? I haven't got the engine back together yet and would like to know what to expect.

                Thanks

                Dan Leslie
                Dan,

                Have you been reading up on how to improve your engine's performance? I would recommend doing just that if you haven't. See post 6 in this thread for some recommendations from Duke:

                https://www.forums.ncrs.org/showthread.php?t=65121

                Joe

                Comment

                • Duke W.
                  Beyond Control Poster
                  • January 1, 1993
                  • 15678

                  #9
                  Re: L48 1.6 ratio rocker arms, carburetor adjustment

                  The L-48 can be easily converted to a "Special 300 HP" configuration (see the Fall 2010 Corvette Restorer), but it needs a full dual exhaust system.

                  Duke

                  Comment

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