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  1. #11
    Registered User
    My Boats:
    Beat up ole Sleekcraft
    Join Date
    Feb 2008
    West edge of the Pacific

    Bandit my 2 cents

    Joe its like when they brought out the QSB 480hp they moved the HP peak further up on the rpm band so they could keep the same gearbox as the QSB 420hp without the gear breaking. Its torque that breaks stuff not horsepower.

  2. #12
    Join Date
    Mar 2008
    torque vs horsepower...

    Think of it this way,

    Say your turning an engine over with a breaker bar and socket on the harmonic balancer bolt. Torque is how much force you are applying to the handle of the breaker bar - if you use a longer breaker bar, you can apply more force, apply too much force, the bolt breaks of and you may put the breaker bar through the garage door (don't ask me how I know this).

    Horsepower would be the work you could exert in a given amount of time to move the boat forward. Torque is force in the radial direction against resistance (no resistance = no torque; think about the same breaker bar and socket turning the same engine over with the plugs removed - take a lot less force), horsepower is force times speed divided by time (or torque times horsepower).

    Changing gear ratios is like changing the length of the breaker bar - higher gear (ie going from 1.98:1 to 1.5:1), less mechanical advantage is like using a shorter breaker bar.

    What will break the gears in the drive is torque - high torque engine at low speed / rpm (the speed range where there is the most resistance). More cam actually helps in this regard because it kills low end torque (can also make the boat a major DOG out of the hole), as can a ventilated prop (let's the prop slip and reduces the torque the drive feels) and especially a light hand out of the hole. As for reversion (sucking water up into the engine) it gets very complicated when you get close to the line. The only way to really know, is to set it up, run it (in the water), let it idle for a while. if it's pretty bad, you can usually hear it load up at low idle, then it will clear up and run fine at a little higher rpm "idle". There's really no substitute for running at your low set idle for a little while and then pulling a manifold to see if there's water at the head...

    Hope this helps...

  3. #13
    Registered TYPHOON's Avatar
    My Boats:
    Join Date
    Feb 2001
    Edison NJ USA
    So what would be a good cam for this motor? And yes it has aluminum heads.

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