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Compression ratio

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  • Charles
    In the absence of any other indication that I can find I have worked out from a detailed examination of the drawings, some 2-D CAD and arithmetic, the design
    Message 1 of 9 , Feb 2, 2010
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      In the absence of any other indication that I can find I have worked out from a detailed examination of the drawings, some 2-D CAD and arithmetic, the design compression ratio of the Seagull would be about 3.5:1. This seems to me to be extremely low.

      Fortunately, the combustion chamber in the Hemingway castings is smaller and would give a ratio of 5:1 if the head is machined to leave the cavity at the depths shown on the drawing.

      However, the castings are a bit short of metal round the plug, and to avoid a break-out into the water space, I may need to machine less of the underside and more off the top, increasing the chamber volume, perhaps to a compression ratio of 4:1, and it may be that the only way to avoid this would be to use the little #10x40 (3/16") plugs instead of the 1/4" ones specified.

      What compression ratio would be suitable for an engine such as the Seagull, which is intended to be mild mannered (Westbury says 'docile')?
    • james wells
      Hello Charles, I can t definitely answer for any Westbury design but on slightly larger engines I ve found that a C/R of around 6 to1 gave reasonably easy
      Message 2 of 9 , Feb 2, 2010
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        Hello Charles,
        I can't definitely answer for any Westbury design but on slightly larger engines I've found that a C/R of around 6 to1 gave reasonably easy starting and economy.
         
        Best wishes
        James Wells
        Saudi Arabia

        From: Charles <charles@...>
        To: ETWestburyEngines@yahoogroups.com
        Sent: Wed, 3 February, 2010 3:11:54
        Subject: [ETWestburyEngines] Compression ratio

         

        In the absence of any other indication that I can find I have worked out from a detailed examination of the drawings, some 2-D CAD and arithmetic, the design compression ratio of the Seagull would be about 3.5:1. This seems to me to be extremely low.

        Fortunately, the combustion chamber in the Hemingway castings is smaller and would give a ratio of 5:1 if the head is machined to leave the cavity at the depths shown on the drawing.

        However, the castings are a bit short of metal round the plug, and to avoid a break-out into the water space, I may need to machine less of the underside and more off the top, increasing the chamber volume, perhaps to a compression ratio of 4:1, and it may be that the only way to avoid this would be to use the little #10x40 (3/16") plugs instead of the 1/4" ones specified.

        What compression ratio would be suitable for an engine such as the Seagull, which is intended to be mild mannered (Westbury says 'docile')?


      • tedhansen23
        3.5 does seem a bit low....I generally use about 4.5:1. It doesn t really matter all that much unless you are intendng to try to produce more power. All that
        Message 3 of 9 , Feb 3, 2010
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          3.5 does seem a bit low....I generally use about 4.5:1. It doesn't really matter all that much unless you are intendng to try to produce more power. All that is really required of most of these little engines is that they start easily and run smooth and anywhere in the 3-4-5:1 range will do that.


          --- In ETWestburyEngines@yahoogroups.com, james wells <terakunene@...> wrote:
          >
          > Hello Charles,
          >
          > I can't definitely answer for any Westbury design but on slightly larger engines I've found that a C/R of around 6 to1 gave reasonably easy starting and economy.
          >
          > Best wishes
          > James Wells
          > Saudi Arabia
          >
          >
          > ________________________________
          > From: Charles <charles@...>
          > To: ETWestburyEngines@yahoogroups.com
          > Sent: Wed, 3 February, 2010 3:11:54
          > Subject: [ETWestburyEngines] Compression ratio
          >
          >  
          > In the absence of any other indication that I can find I have worked out from a detailed examination of the drawings, some 2-D CAD and arithmetic, the design compression ratio of the Seagull would be about 3.5:1. This seems to me to be extremely low.
          >
          > Fortunately, the combustion chamber in the Hemingway castings is smaller and would give a ratio of 5:1 if the head is machined to leave the cavity at the depths shown on the drawing.
          >
          > However, the castings are a bit short of metal round the plug, and to avoid a break-out into the water space, I may need to machine less of the underside and more off the top, increasing the chamber volume, perhaps to a compression ratio of 4:1, and it may be that the only way to avoid this would be to use the little #10x40 (3/16") plugs instead of the 1/4" ones specified.
          >
          > What compression ratio would be suitable for an engine such as the Seagull, which is intended to be mild mannered (Westbury says 'docile')?
          >
        • Jaime Quevedo
          Here the main question will be spark plug Vs glow plug. If glow plugs are considered, then you need a higher compression ratio, more like 10:1 or higher,
          Message 4 of 9 , Feb 3, 2010
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            Here the main question will be spark plug Vs glow plug.
            If glow plugs are considered, then you need a higher compression ratio, more like 10:1 or higher, though some engines can run on 9:1 but do not idle well.
            For Spark plugs, consider 5:1 - 6:1 as the lowest you can make an engine run, here some problems with valve seats present a greater challenge.

            I prefer to build engines with compression ratio of 8.5:1 - 9:1.
            Check your math again and make sure you leave enough space for the valves not to hit the cylinder liners, take in consideration valve lift, in the Wallaby engine ET Westbury left no room for the valve lift and higher compression, so had to be very careful centering head, combustion chambers and cylinder liners.


            Cheers.

            Jaime.
            On Feb 2, 2010, at 4:11 PM, Charles wrote:

            In the absence of any other indication that I can find I have worked out from a detailed examination of the drawings, some 2-D CAD and arithmetic, the design compression ratio of the Seagull would be about 3.5:1. This seems to me to be extremely low.

            Fortunately, the combustion chamber in the Hemingway castings is smaller and would give a ratio of 5:1 if the head is machined to leave the cavity at the depths shown on the drawing.

            However, the castings are a bit short of metal round the plug, and to avoid a break-out into the water space, I may need to machine less of the underside and more off the top, increasing the chamber volume, perhaps to a compression ratio of 4:1, and it may be that the only way to avoid this would be to use the little #10x40 (3/16") plugs instead of the 1/4" ones specified.

            What compression ratio would be suitable for an engine such as the Seagull, which is intended to be mild mannered (Westbury says 'docile')? 


          • tedhansen23
            I must disagree. Spark ignition engines will run quite well with much lower than 5:1, in fact there are designs for non-compression engines which also can be
            Message 5 of 9 , Feb 3, 2010
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              I must disagree. Spark ignition engines will run quite well with much lower than 5:1, in fact there are designs for non-compression engines which also can be made to run OK.

              --- In ETWestburyEngines@yahoogroups.com, Jaime Quevedo <quevedo.jaime@...> wrote:
              >
              > Here the main question will be spark plug Vs glow plug.
              > If glow plugs are considered, then you need a higher compression
              > ratio, more like 10:1 or higher, though some engines can run on 9:1
              > but do not idle well.
              > For Spark plugs, consider 5:1 - 6:1 as the lowest you can make an
              > engine run, here some problems with valve seats present a greater
              > challenge.
              >
              > I prefer to build engines with compression ratio of 8.5:1 - 9:1.
              > Check your math again and make sure you leave enough space for the
              > valves not to hit the cylinder liners, take in consideration valve
              > lift, in the Wallaby engine ET Westbury left no room for the valve
              > lift and higher compression, so had to be very careful centering head,
              > combustion chambers and cylinder liners.
              >
              >
              > Cheers.
              >
              > Jaime.
              > On Feb 2, 2010, at 4:11 PM, Charles wrote:
              >
              > > In the absence of any other indication that I can find I have worked
              > > out from a detailed examination of the drawings, some 2-D CAD and
              > > arithmetic, the design compression ratio of the Seagull would be
              > > about 3.5:1. This seems to me to be extremely low.
              > >
              > > Fortunately, the combustion chamber in the Hemingway castings is
              > > smaller and would give a ratio of 5:1 if the head is machined to
              > > leave the cavity at the depths shown on the drawing.
              > >
              > > However, the castings are a bit short of metal round the plug, and
              > > to avoid a break-out into the water space, I may need to machine
              > > less of the underside and more off the top, increasing the chamber
              > > volume, perhaps to a compression ratio of 4:1, and it may be that
              > > the only way to avoid this would be to use the little #10x40 (3/16")
              > > plugs instead of the 1/4" ones specified.
              > >
              > > What compression ratio would be suitable for an engine such as the
              > > Seagull, which is intended to be mild mannered (Westbury says
              > > 'docile')?
              > >
              > >
              > >
              >
            • Jaime Quevedo
              I guess it depends on the application, if you intend to use the engine to power a model boat, you will need more than 5:1, if all you do is run it in a stand
              Message 6 of 9 , Feb 3, 2010
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                I guess it depends on the application, if you intend to use the engine to power a model boat, you will need more than 5:1, if all you do is run it in a stand then 5:1 may do.
                Cheers

                Q is in the move.


                On Feb 3, 2010, at 8:20 AM, "tedhansen23" <tedhansen@...> wrote:

                 

                I must disagree. Spark ignition engines will run quite well with much lower than 5:1, in fact there are designs for non-compression engines which also can be made to run OK.

                --- In ETWestburyEngines@ yahoogroups. com, Jaime Quevedo <quevedo.jaime@ ...> wrote:
                >
                > Here the main question will be spark plug Vs glow plug.
                > If glow plugs are considered, then you need a higher compression
                > ratio, more like 10:1 or higher, though some engines can run on 9:1
                > but do not idle well.
                > For Spark plugs, consider 5:1 - 6:1 as the lowest you can make an
                > engine run, here some problems with valve seats present a greater
                > challenge.
                >
                > I prefer to build engines with compression ratio of 8.5:1 - 9:1.
                > Check your math again and make sure you leave enough space for the
                > valves not to hit the cylinder liners, take in consideration valve
                > lift, in the Wallaby engine ET Westbury left no room for the valve
                > lift and higher compression, so had to be very careful centering head,
                > combustion chambers and cylinder liners.
                >
                >
                > Cheers.
                >
                > Jaime.
                > On Feb 2, 2010, at 4:11 PM, Charles wrote:
                >
                > > In the absence of any other indication that I can find I have worked
                > > out from a detailed examination of the drawings, some 2-D CAD and
                > > arithmetic, the design compression ratio of the Seagull would be
                > > about 3.5:1. This seems to me to be extremely low.
                > >
                > > Fortunately, the combustion chamber in the Hemingway castings is
                > > smaller and would give a ratio of 5:1 if the head is machined to
                > > leave the cavity at the depths shown on the drawing.
                > >
                > > However, the castings are a bit short of metal round the plug, and
                > > to avoid a break-out into the water space, I may need to machine
                > > less of the underside and more off the top, increasing the chamber
                > > volume, perhaps to a compression ratio of 4:1, and it may be that
                > > the only way to avoid this would be to use the little #10x40 (3/16")
                > > plugs instead of the 1/4" ones specified.
                > >
                > > What compression ratio would be suitable for an engine such as the
                > > Seagull, which is intended to be mild mannered (Westbury says
                > > 'docile')?
                > >
                > >
                > >
                >

              • Corey Renner
                The advantages of low-compression seem to be that you can achieve a lower idle speed with an equivalent flywheel mass, and your model jumps around less. The
                Message 7 of 9 , Feb 3, 2010
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                  The advantages of low-compression seem to be that you can achieve a lower idle speed with an equivalent flywheel mass, and your model jumps around less.  The disadvantage is decreased power.  I would consider 3:1 to be a reasonable compression ratio for an engine that doesn't do any work other than amusing it's owner.

                  c

                  On Wed, Feb 3, 2010 at 11:41 AM, Jaime Quevedo <quevedo.jaime@...> wrote:


                  I guess it depends on the application, if you intend to use the engine to power a model boat, you will need more than 5:1, if all you do is run it in a stand then 5:1 may do.
                  Cheers

                  Q is in the move.

                • Malcolm
                  I recall that my 1955 BSA 600cc side valve operated with compression ratio s of about 5.7:1 and the 500cc M20 with 5:1 and produced 18bhp from 600cc s and
                  Message 8 of 9 , Feb 3, 2010
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                    I recall that my 1955 BSA 600cc side valve operated with compression ratio's of about 5.7:1 and the 500cc M20 with 5:1 and produced 18bhp from 600cc's and 13bhp from the 500s - reliable but not exciting!

                    I have a related question... I have a seal major casting set in the workshop which I am going to get "serious" about later in the year. My intent is to use it to power a "diesel electric" loco (e.g. have the seal drive an alternator)... I figure I need no more than 0.3bhp output (from the genny) to make the project work, but no-one seems to have any idea about the power the seal major might produce (even with standard compression)...

                    (my reasoning to the project power requirement is that the (large) winning 5-inch scale locos in the IMLEC efficieny trials typically make no more than 1bhp...

                    are there any people here with an opinion (or better yet facts)on what a seal major (or other 30cc sidevalve) will make????

                    Malcolm
                  • thomas.r.roach@sympatico.ca
                    We should remember that when Westbury was active, the quality of the fuel that was sold was very poor and only one grade was available. Compare the
                    Message 9 of 9 , Feb 3, 2010
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                      We should remember that when Westbury was active, the quality of
                      the fuel that was sold was very poor and only one grade was
                      available. Compare the compression ratio of cars made in the 40's and
                      50's and you will find there was not a lot of difference between their
                      compression ratio and that employed in Westbury's model engines.
                      Further more, the small size of the combustion chamber would mean that
                      the engines would be liable to "knock" if the compression ratio was
                      even moderately increased.

                      Tom Roach
                      695 Beechwood Drive
                      Waterloo, Ontario
                      N2T 2M7
                      519 746 5324
                      mailto:thomas.r.roach@...
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