Single exhaust system for a 3 cylinder two stroke
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  1. #1
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    Single exhaust system for a 3 cylinder two stroke

    Hi Bill,
    In these days I'm reflecting about the theory involved in single ex systems used in 3 cylinder two stroke engines.
    According to my knowledge best results with this engines can be achieved only with three separate ex. chambers like in old 4 cylinders GP 500 bikes.
    The dedicated chamber can extract maximum power from each cylinder attending that the pressure waves and consequently resonant effects can be used at their best.
    In single pipe applications the pressure waves can be used only in minimal part attending that ex ports are not opening and closing at the same time. In a 120 spaced crank we can have at the same time a port completely closed, one partially closed and one fully open. To some extents a three into one pipe could be also detrimental if you think that a return wave could arrive in the worst momen,t for example when a port has started to open..............
    I think that the single pipe in multicylinder engines can be only used like a big muffler with very few tuning options (principally stinger diameter)
    Consequently the power output of these engines relies principally on primary and secondary compression ratios and on port timing and dimension. The influence of the pipe for performance is very questionable.
    What do you think Bill about these my ideas?
    Thank you
    Michele

  2. #2
    PWCToday Newbie williamsburgjim's Avatar
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    Re: Single exhaust system for a 3 cylinder two stroke

    ...good question! Subscribed!

  3. #3
    PWCToday.com Is My Home Away From Home Mr. Bill's Avatar
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    Re: Single exhaust system for a 3 cylinder two stroke

    I think you either decide to run one chamber for all three clys, or you choose to have three seperate headpipes, chambers and stingers all running into one waterbox on a pwc.

    The big rpm numbers will come from the three seperate dry pipes, each pipe is tuned to the clyinder it is scavenging.

    Go look at the tripe clyindered drag and ice sleds..........Those triple dry pipes obiviously are helping the performance or those sleds would not be going 165 MPH on the ice lakes.
    Bill O'Neal
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  4. #4
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    Re: Single exhaust system for a 3 cylinder two stroke

    Hi Bill,
    Thank you for your like always competent answer.
    I know that the big hp numbers are coming from the separate pipes. In my previous mail I wanted your opinion about the theory behind the single pipe engine (three cylinders in a single pipe).I think that this solution doesn't use at its best the resonant effect of the expansion chamber for scavenging the cylinders and acts like a big muffler. In practice these engine configurations are very similar to the ones used 50 or more years ago and actually in outboard engines when expansion chambers benefical effects weren't fully known.
    I wait for your feedback
    Thank you like always
    Michele

  5. #5
    PWCToday.com Is My Home Away From Home Mr. Bill's Avatar
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    Re: Single exhaust system for a 3 cylinder two stroke

    You are correct, there is not much of any real "scavenging" going on like a tuned pipe would give you. Cubic inches is the big thing with triples and they rely on a bigger cc motor to give them power to match a twin with a tuned exhaust.
    Bill O'Neal
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    For repairs and/or parts and appointments only:
    626 914 9509 M-F 10 am to 5 pm PST, ask for Chris.

    Always speak your mind because those who mind don't matter and those who matter don't mind.

  6. #6
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    Re: Single exhaust system for a 3 cylinder two stroke

    Hi Bill.
    From what I understand also a twin with a tuned pipe is not the best solution In a twin when one ex port is fully closed the other is fully opened, So only a cylinder can take full advantage from a tuned pipe becouse if the sonic waves are good for a cylinder (aiding the scavenging when ex port opens and pushing back in the cylinder lost fresh charge when ex port is closing) they are not matched with the other cylinder.
    I'm right Bill?
    Thank you
    Michele

  7. #7
    PWCToday.com Is My Home Away From Home Mr. Bill's Avatar
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    Re: Single exhaust system for a 3 cylinder two stroke

    Yes, again, you are correct. Having one exhaust port open during scavenging, and another pushing exhaust gasses through the same exhaust chamber at the same time is not going to work out very well.

    A twin is a 180 degree engine, whereas the triple is a 120 degree engine. 120 degree engines have an overlap between clyinders when more than one port is open at the same time. One of those partially open ex ports will have a piston travelling up to cover the port while the other partially opened exhaust port with have already had the piston pass the port and be headed for the bottom of the cases.
    Bill O'Neal
    www.watercraftmagic.net
    For repairs and/or parts and appointments only:
    626 914 9509 M-F 10 am to 5 pm PST, ask for Chris.

    Always speak your mind because those who mind don't matter and those who matter don't mind.

  8. #8
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    Re: Single exhaust system for a 3 cylinder two stroke

    Hi Bill,
    On a Kawasaki triple it seems as if they designed a some what tuned pipe. Is this accurate or just a muffler? On a Yamaha triple the stinger diameter is much larger that the Kawasaki stinger. Is this because the Kawasaki pipe is a tuned pipe configuration where as the Yamaha is just a muffler? Can they both be tuned by adding or restricting water? What would happen if the Yamaha had more of a Kawasaki style pipe?

    Thankyou
    Blockhead Racing Team

  9. #9
    PWCToday.com Is My Home Away From Home Waxhead's Avatar
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    Re: Single exhaust system for a 3 cylinder two stroke

    There is so much misinformation in this thread its astounding.
    Have a look at triple outboard and see how its pulse tuned
    better still read this and you will realise that the kawi system is crap and the yamaha system is actually quite good
    http://members.iinet.net.au/~pauldaw...s_exhausts.PDF
    Www.waxracingproducts.com
    All your billet vintage parts in one place

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