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Thread: RPM'S

  1. #1
    tomcat_m's Avatar
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    RPM'S

    How to put this?
    I'm 40ish so 15-20 years ago i had a few bikes like a gsxr and a ninj
    So I got this brandnew sho waverunner( still havent tryed it)
    I just dont understand this
    All the post I read you can only rev it up to 7000-8000 then you have to spend alot of money to reflash the computer etc
    The sho engine is a 4 cylinder engine just like a bike
    A bike engine can go to 12-14000 rpm without any worrys about the engine blowing up so why is the waverunner set so low in rpms?
    I guess bike engines are better?
    Thanks still trying to figure this out and cant wait till spring till I get to play
    Mike


  2. #2
    lets race.... mikeFZR's Avatar
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    I think it is because the ski has to work harder to move because there is more resistance on water than on land with a bike. The sho engine puts out plenty of power so don't let the rpm numbers fool you.

  3. #3
    tomcat_m's Avatar
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    I understand about the resistance of the water but the engine doesnt know that
    Why is everyone spending lots of money on the valve train and ecm so they can get higher revs
    I'm not saying I will not be happy with the sho
    The bike engine seems like they are better built and cost slighty less or the same
    Mike

  4. #4
    volltrex's Avatar
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    Quote Originally Posted by tomcat_m View Post
    The bike engine seems like they are better built and cost slighty less or the same
    Mike
    The older FXHO uses the MR1 motor......which is based on the R1 bike motor. There are many differances but essentially the same base workings.
    The R1 will go to over 14000rpm if memory serves me correctly, but the MR1 will go to a shade over 10000rpm.
    The R1 will rarely be WOT for very long, where as a motor in a pwc spends alot of it's time at the top of it's rpm range, so keeping the revs down ensures decent motor life.
    I consistently do WOT runs of around 20 mins.........a bike motor just wouldn't get this kind of punishment
    Also.....the SHO uses a 1.8 motor.........much larger then most bikes, so there is no need to use high rpm's

  5. #5
    Boilerman Bill BPnta's Avatar
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    I bet it has a lot to do with the pump's design for efficiency as well. The 10,000 RPM MR1 motor has a gear reducer as well to bring the RPMs down before it gets to the pump.

    But like volttex said longevity is the main issue. At 10,000 RPM that's 333 strokes a second! You'll probably have around 75% of your skis hours at WOT

    Almost a million strokes an hour

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by BPnta View Post
    ...At 10,000 RPM that's 333 strokes a second!

    ...Almost a million strokes an hour
    How did you get those numbers?

    10,000RPM = 175 revolutions per second

    3600 seconds in an hour => 167 * 3600 = 600,000 revs per hour
    (same as 10,000RPM * 60 minutes)

    4 cylinders * 600,000 revolutions each per hour = 2,400,000 * 2 strokes per rev => 4,800,000 strokes per hour across the four cylinders

  7. #7
    Boilerman Bill BPnta's Avatar
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    Quote Originally Posted by K447 View Post
    How did you get those numbers?

    10,000RPM = 175 revolutions per second

    3600 seconds in an hour => 167 * 3600 = 600,000 revs per hour
    (same as 10,000RPM * 60 minutes)

    4 cylinders * 600,000 revolutions each per hour = 2,400,000 * 2 strokes per rev => 4,800,000 strokes per hour across the four cylinders
    I was treferring to one cylinder since they are not likely to fail all at once

    10,000 revolutions/minute times 2 strokes/revolution times 60 minutes/hr

    equals 1,200,000 but I said 75% of the time was WOT. 75% of 1,200,000 is 900,000. To make up for the time it wasn't WOT, I estimated it to be around a million

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