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  • Engine: Avanti pistons

    Why did 57-58 supercharged engines have 7.8 comps and 63-64 could use 9 or more comp. ratio on R2 and R3s.I have a 58 super packard engine less supercharger stuff with 4 barrel manifold.If I use flat top Avanti pistons for R1/R2,what will that raise compression to?Thanks,Neil
    NEIL G.

  • #2
    There can be several answers to your question and the answer depends on which heads are on your engine and which head gaskets are installed. Depending on the combustion chamber volume, the compression ratio can be anywhere from around 9.25 to 10 to 1. There are also half dish pistons available that won't raise the compression enough to cause detonation problems. Keep in mind that the R series engines were built when we had higher octane gas available than what is available today so a half dish piston may be the way to go. Bud

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    • #3
      Originally posted by Bud View Post
      Keep in mind that the R series engines were built when we had higher octane gas available than what is available today so a half dish piston may be the way to go. Bud
      That's what I did in my R-1 Avanti.
      My engine rebuilder..who did a lot of race engines..said it will take off some 15-20 hp and lower the ratio to 9 or 9.25 to 1.
      But it will be much happier with todays (and tomorrow's) gas.
      63 Avanti R1 2788
      1914 Stutz Bearcat
      (George Barris replica)

      Washington State

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      • #4
        Don't forget the camshaft. The reason the R1-R2 and the regrind R2+ can live with higher static compression is they are much longer duration and thus lower the dynamic compression.

        If you are planning to use the '57 camshaft, do not use flat top pistons.

        jack vines
        PackardV8

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        • #5
          Restoring a car to drive & enjoy means making it drivable & practical. Too often I have seen an engine built for the drag strip installed into a restored car, and the owner ends up leaving it in the garage or trailering it to meets because poor drivability and high octane requirements. It is very possible to build a car you will enjoy using which still has enough power to be fun.
          Barry'd in Studes

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          • #6
            There isn't much gained with Avanti pistons if you retain the stock cam that's in there.
            They were all played out about the same time the valves floated which was less than 4800 rpm.
            Also the supercharger (McCulloch) belt will slip anything above that. If the belt didn't slip, then the internal ball drive will slip as the spring pack pressure was way less than on the Paxton.
            The pulley kick-down solenoid is factory set to regulate the boost to 3 1/2 lbs.....you will see 5 lbs on full throttle, but once you level the rpms, the spring loaded diaphragm bleeds the boost to the pulley, and the supercharger slows back down. I have and can modify the solenoid for more boost and the springs to the races can be beefed up to produce more boost,.....but, you still run into the belt slippage problems
            Bez Auto Alchemy
            573-318-8948
            http://bezautoalchemy.com


            "Don't believe every internet quote" Abe Lincoln

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            • #7
              Thanks for the replys.I think the only mods I will do to this engine will be R-1 type cam and R-3 intake valves. Neil
              NEIL G.

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              • #8
                While most of us will assume you mean to add better valve springs with the R1 cam, it bears saying. The R1-R2 valve springs our Stude vendors sell are the minimum you need and another few pounds of seat pressure would be better still, as the R3 intakes are heavier than R1-R2.

                jack vines
                PackardV8

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