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IndustryArena Forum > Hobby Projects > I.C. Engines > 2-stroke ported OPOC engine (125cc x 2)
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  1. #49
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    allo uuu,

    ok, hmmm, what do you think: the air-fuel mixture is going to be rushing in just as the exhaust is being cleared, all ports are open, and the spark fires. i'm a bit concerned about that. i don't mind having 2 sets of magnet-controlled ignition relays: there are 2 gears, one on each side, so they can be mounted either side, that's not a problem.

    eventually this will be converted to diesel so it then becomes moot, but i have to find glow plugs about the same size as the sparks, with a 14mm thread diameter, to do that. and mess about with the cylinder head (probably weld and then grind!) to increase the compression ratio. ahh what fun...

    [update:] http://www.dlenginesaustralia.com/dl...g-adaptor.html

    ah ha! i have a cunning plan! ha. that, also, would solve the problem of the (standard car) diesel glow plugs sticking into the cylinder and bashing the top of the piston head. a shorter, smaller R/C glow plug is of course designed for a much smaller cylinder.

  2. #50
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    The easiest ignition I've found is the GM HEI module. Here is a good link for adapting them
    General Motors HEI Ignition Module For Points
    In this type of use you only use points as a switch, they carry no real current like points and coil do.

    I have a couple of Pan Head Harleys that I used them on and ended the point problem .

  3. #51
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    I see your point with the spark at the wrong time.

    To increase the compression ration, could you make up a circular disc/plug to fit in the top of the cylinder, attached to the bottom of the head? With a hole for the glow plug to stick into, this would reduce its projection into the space and ease your clearance problems. It would give you the opportunity to experiment with different ratios, by having a selection of disc/plugs, much like some model engines have a counter-piston.

  4. #52
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    How about externally adjustable compression ratio? www.psipowerinc.com/heads.htm

    I realize these are two-stroke snowmobile heads. I just intended to bring forth the idea.

    FYI, a 340cc two-stroke, naturally aspirated snowmobile engine in race trim on gasoline fuel produces~115 hp (86kw). Thats 338hhp(253kw)/litre

    Dick Z
    DZASTR

  5. #53
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    lkcl FYI DeltaHawk Diesel Engines

    Dick Z
    DZASTR

  6. #54
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    Crank case

    ok, well just an update: i've done the DXF drawings for the crank case that these big-bore kits will bolt onto. i used python (!) and a module called sdxf.py and i've created the crank case as 4 "slices" out of 12mm thick 100x75mm mild steel which the bolts will go through and sandwich onto the 70cc cylinders.

    pictures of the 4 DXF drawings are here: http://lkcl.net/engine/ - i will put the python program up online as well at some point, including the one that generates the trilobes.

    in theory i could actually make the entire cylinder this way, simply by making more slices, then putting in a steel liner to hold them all stably together.

    oh, one other thing: i found some 14mm brass adapters that can take the tiny RC-model glow-plugs. i figured that as this needs to be diesel, to start from there straight away. the reason for using tiny glow-plugs is to ensure that they don't protrude into the cylinder, as the piston is going to be right up against the top.

  7. #55
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    @IKCL, you don't really mean it literally when you say, "as the piston is going to be right up against the top." You need a small space there for combustion to take place and to keep from having the pistons making physical contact with the heads.

    The GM ignition modules will work with optical sensors or hall sensors also, not just points. Forgot to mention that in the last post.

  8. #56
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    Quote Originally Posted by RICHARD ZASTROW View Post
    FYI, a 340cc two-stroke, naturally aspirated snowmobile engine in race trim on gasoline fuel produces~115 hp (86kw). Thats 338hhp(253kw)/litre

    Dick Z
    Before MotoGP switched to four strokes the 500cc naturally aspirated, two stroke, V4 engines were similarly producing almost 200 hp, or 400hp/L.

  9. #57
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    Some people may have realized that some newer cars are said to be using the “Atkinson cycle,” especially on hybrids. The key characteristic of the Atkinson cycle is finishing all four “strokes” of an engine cycle with one turn of the crankshaft, which is more cost-effective. The Information on the Atkinson cycle was made clear. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.

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