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  1. #1
    SingTH's Avatar
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    Red face Anyone run with seadoo Crankshaft stroker

    Any ideas for make the 4-tec stroker crankshaft.


  2. #2
    ROTAX RACING performance
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    I have a stroker crank for the 4-tec engine, for use with stock block, but you also need special pistons and rods, and it's not a low budget option.

  3. #3
    SingTH's Avatar
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    Quote Originally Posted by mrracing View Post
    I have a stroker crank for the 4-tec engine, for use with stock block, but you also need special pistons and rods, and it's not a low budget option.
    How is long? +2 , +3 , +......mm. what is performance??

    Thanks

    Dumri

  4. #4
    Quote Originally Posted by mrracing View Post
    I have a stroker crank for the 4-tec engine, for use with stock block, but you also need special pistons and rods, and it's not a low budget option.
    How many cc's does it bring it too??

  5. #5
    Every adventure comes to an end........ Not Today! wreckingball's Avatar
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    If you stroke a motor, doesn't it lower the RPM's you can run the motor? If so, wouldn't that be counter productive to going fast? Or would it be suited to someone who just wants to make massive power out of the hole in a drag race?

  6. #6
    Banned User
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    Its all about the combo.....

  7. #7

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    Quote Originally Posted by Mike H View Post
    Its all about the combo.....

    exactly. and tuning ability. this is copied and pasted from a buddy of mine that has developed piggy back ECU's for use on can-am ATV's (sea-doo's cousin):


    First, for the novice:

    Terminology is always interchanged, but technically they are different.
    *Spark knock- too advanced timing causing explosion too soon and piston to tilt and skirt knock on cylinder
    *Detonation- uncontrolled burn/ explosion (too fast)
    *Preignition- something else ignites the mixture before spark even occurs

    The whole point of advancing timing is because the piston moves so fast and it takes time for the spark to move from the coil out through to the spark plug electrode (tip) And it takes time for the flame to start burning. You have to start the electricity early to get there and light the fire at the same time as the piston gets there. Since this is time based, and the piston speed changes (rpm), the firing time has to change too. That is why there is an advance curve. (timing advances as rpm increases)

    And for a stroked motor:

    There is no easy answer but to explain what is happening and which way to go: With a stroker, timing needs to be advanced more. (in comparison to the same compression)

    There is a few things going on.
    First, because of the longer distance the piston travels now, the piston position vs crank degrees also changed. The crank still moves 180* for 1 piston stroke, but the piston travels more in the same crank movement. So the piston is now always in a different spot throughout the whole crank turn than before.

    But that's not the main reason for an ignition timing change.

    With a bigger lower rod / crank arc, the piston will be at Tdc longer. (More crank degrees go by as the piston stays at tdc) Therefore it reaches tdc sooner (in relation to crank degrees) than before.

    So if you fired at say 10* btdc before the stroke change, the piston may already be at top dead now. And you would now fire too late. So you would need to advance the timing.

    *But* there is one glitch * -because more time is spent at tdc, there is also more time to fire and start the burn before the piston starts moving down again from tdc. This may make up for the now late timing? It depends on the actual stroke change.


    Flame travels in time, not crank degrees. And for best power, you want the flame to be pushing the piston down as soon as the upforce is gone. Fighting the upforce is lost power (and knocking) if the flame pushes the piston too late - you loose the initial (and greatest) thrust You loose power because the mixture compression is dropping lower because the chamber space is getting bigger as the piston moves from tdc down.

    To be accurate, you would have to physically measure the piston from the deck at crank position 5*, 10*, 15* etc all the way to 40*. Then after the stroke- put the piston at the same positions and measure the new crank degrees. Set your timing for firing at the same piston to deck heights for the fuel you were using.

    But now you have higher compression because of the new pistons you just put in and also because of the stroke changing the swept volume of the cylinder. And if the heads and cam add more air than before, the pressures are much much higher. so it may end up being to much advance to go by piston height. Unless you keep moving to better/ higher octane fuel. But if you are just comparing a stroke change on a motor- timing needs to be advanced.

    Its all in getting the timing right. And why timing is so important in getting maximum power. Too early or too late is lost power. And because of the electricity moving, piston speed and the flame is all time based (not crank degree based) Fuel/ Octane is also time based. And changing the fuel allows another way of tuning when the flame pushes the piston down.

  8. #8

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    Quote Originally Posted by SingTH View Post
    Any ideas for make the 4-tec stroker crankshaft.
    Rotax sure has Long block for sale!

  9. #9
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    You also have to take into account the maximum piston speed, if you increase the stroke you move the piston more for each revolution, this speeds up the piston and if overdone you could stuff it.

    Sean

  10. #10
    SingTH's Avatar
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    Talking

    Thanks for everyone, so It is not easy for go faster with long stroke.

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