Low Compression v/s High Compression

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  • Sidehacker
    Senior Member
    • Sep 2012
    • 235

    #1

    Low Compression v/s High Compression

    Will a high compression u motor get relatively the same top speed crusing as a low compression head.
  • JoJo357
    Senior Member
    • Feb 2016
    • 3175

    #2
    *Keith, hope this answers your question.

    *Model U Flathead 74c.i. 1209cc-- 5.0:1 Compression Ratio.
    32.5 hp @ 4200 rpm. 135 km/h = 84mph ?


    *Model UL Flathead 74c.i. 1209cc -- 5.2:1 Compression Ratio.
    37.5 hp @ 4200 rpm. 135 km/h = 84mph ?



    *M.A.D.*

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    • chuckthebeatertruck
      Senior Member
      • Jun 2018
      • 658

      #3
      Yes.

      the compression is laughably low.

      Comment

      • Sidehacker
        Senior Member
        • Sep 2012
        • 235

        #4
        That totally answers that question now since a 3 speed and a four speed have 1to 1 on top gears do they also have same top speed.

        Comment

        • chuckthebeatertruck
          Senior Member
          • Jun 2018
          • 658

          #5
          No.

          The theory says they can cover the same distance at the same rpm in top.

          In reality, the higher horsepower bike will pull more gear.

          What does that mean?

          Torque gets you moving -- horsepower gets you going.

          A lower compression, lower horsepower bike will not pull as many rpm in top as a higher compression, higher horsepower bike (if all else is identical).

          They will have the same theoretical speed -- but it won't ever quite work out that way.


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