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Thread: Yamaha 6h5 50hp, more power?

  1. #1
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    Jul 2022
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    Default Yamaha 6h5 50hp, more power?

    Hi, need some help to squeeze more power from my 50hp. The boat is 15ft v-hull, 400lb without engine. Engine is light, short rig without trim. Boat now has yamaha 30hp 3cyl engine, top speed 35knots, jumps on plane.

    -Offset chamber head milling, how much?
    -DIY exhaust tuner, shape? Milling the tuner at the gasket surface?
    -Bigger carbs, 60hp or 70hp?
    -Milling the intake surface of the block, how much? Or stuffers under the reed cages, or both?
    -Port timing modifications?
    -Ignition system, old style? Or newer style arrow box?
    -Exhaust plate spacer?
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  2. #2
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    Jun 2010
    Panama City, Florida
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    Those are used extensively in the p750 thundercat mod class. In addition to what you're proposing they run bigger pistons, lighten and balance they flywheel (only helps to speed up revs). You'll find a lot more info on Facebook, regrettably, that's where most of the info is shared/stored these days.

    You might try asking in the Facebook group Thundercat Racers North America.

    That 30 yamaha of yours is worth some money.

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