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  1. #1

    Boosting an outboard 2 stroke

    A little off topic but its still a pwc. I having a play with a race boat with a
    30hp mercury outboard. Im looking at getting some more power out of the engine.
    dont even mention props as im well awear of that side of things and have a few
    that i have been playing with. Exhaust side of things, the exhaust runs back
    thru the block and down the leg and out the middle of the prop so as far as im
    awear nothing can be ganed there.
    I have got my hands on some
    110 octane av gas. Im wanting to run with it as see what extra power i can get.
    I am aware that i need to incrase the compression and extra fuel to run it. I
    have the head off and had it cced 25.2cm3 and about 2cm3. Before i removed the
    head i did a compression test at 145psi. the main jet is 155.

    My question is, what compression should I
    aim for[I having the head shaved] and what should i increase the main jet size

    Im sure sure many of you have played
    with this kind of thing before with skis and im hoping the same can be
    transfered to an outboard. Any advice would be appreciated cheers<!-- google_ad_section_end --> <!-- / message -->

  2. #2
    picking up compression will give you more acceleration but no help at top end,if you could design a tuned exhaust dry that would be your biggest gain with some port work,they used to run 35hp and 50 hp modified outboard classes back in the 80s and some of those circle racing boats could hit 75mph with small twin,of course the had moveable expansion chambers and so really awsome custom 2 blade props.

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