2-Stroke HT Bicycle Engine Cross Flow Design

Discussion in 'Motorized Bicycle General Discussion' started by Charged-Reacter, Dec 8, 2009.

  1. Charged-Reacter

    Charged-Reacter New Member

    Dec 12, 2008
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    In a cross flow design 2-stroke engine the piston should be shaped so
    that the incoming fuel mixture doesn't simply flow right over the top of
    the piston and out the exhaust port.
    The flat top piston design would give a faster fuel flow from the fuel
    tank and more fuel wastage?
    The dome shaped piston design would give a slower fuel flow from the
    fuel tank and less fuel wastage?
    Why isn't there a stepped up piston design on the intake side of the
  2. camlifter

    camlifter Active Member

    May 4, 2009
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    Re: 2-Stroke HT Cross Flow Design

    the air fuel mix comes in from the side through the transfer ports, a proper combustion chamber design uses the piston top and cyclinder head shape to promote a full fuel burn, this includes a swirl effect to keep the mix from separating, and give a proper flame front. on a piston port 2 stroke like the ht the actual intake path is down through the case and up around the cyclinder to the top of the piston, if you look down the carb and intake you will never see the top of the piston from that view.
  3. Riding Rich

    Riding Rich New Member

    Aug 14, 2009
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    Re: 2-Stroke HT Cross Flow Design

    Thats correct.
    On my PK80-J with the dome shape piston....
    The crown or rounded piston shape is quite a ways above the top of the jug and the exhaust port.
    In the Serious Porting thread i have drawn this.
    We will see where things are at on the Transfer soon.

    The Air / Fuel mix is sucked in under the piston.
    The the piston compresses the crankcase going down to BDC.
    The transfers open and let the mix in the cylinder above the piston.

    The Transfer ports have a nice angle on one side and at the top of each port.
    This directs the Airflow up to the top of the cylinder and avoids conflict with the exhaust port. ( Called SHORT CIRCUT )

    Also the ports flow at each other causing the mix 2 to collide keeping it in the cylinder and spinning like a tornado.

    Got to realize as well that the amoun of time things are happening at is very quick.

    like in the .00013 fraction of a second.

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