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Thread: power valves?

  1. #1

    power valves?

    after many hours of browsing pics i have noticed that some people have done some kind of mod to there power valves on there 951 engines.

    it looks as though a hole is cut on in the plastic cover and the vacum nipple is then blocked off.

    what does this do and y are people doing it?


  2. #2
    KrunchovXPL-GTX-RX's Avatar
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    When RAVEs (Yamahas use Power Valves, ) were first introduced on the 787 they were operated by engine pressure via a hole in the base that would allow the push from the rising piston to push on the valve via the bellows. When there was enough pressure (ie, RPM) to overcome the upper spring the RAVE valve would open.

    The 947 is equiped with a RAVE solonoid that draws pressure through a check valve from the rear case cavity. It uses this pressure to open the RAVEs on command from the MPEM based on RPM and or the RPM rise (or Delta, if you will). That pressure is applied to the bellows via the small hoses that are on the little nipples (I feel creepy writing that).

    When you see one with the fitting for the hose from the solonoid blocked off they have drilled a hole in the base of the RAVE to allow it to operate manually, so to speak, like a 787. I am not sure why they would choose to drill a hole in the RAVE cap unless it is to be able to see if the valve has opened. They might be using DI caps as they have the hole in them already though they have blue adjusters, I do believe. Either way, I would say it is for visibility.

  3. #3
    It would be interesting to know which people prefer manual rave valves, Or the solenoid route?

  4. #4
    big john's Avatar
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    what is the benefit with manual rave valves ????????????

  5. #5
    SURFnTURF's Avatar
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    You dont rely on a solenoid to activate them.Mechanical means only.

  6. #6
    I wonder why they would block the vacuum source off. The manual valves have a hole in the Mount that lets pressure in to open the valve. The cylinders for the vacuum valves don't have the hole for exhaust pressure to open the valves.

  7. #7
    big john's Avatar
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    would bypassing the electric seleniod and just connecting them to the pressure fitting on the engine case be a better idea, that way they rely on engine pressure only ??????? the more trottle at speed and load the more the rave opens and does its thing ???????

  8. #8
    no they would open at idle, they need to be activated at certain revs, the fitting on the case lets a pulsating action in the line, then there is a one way valve in the line going to the solenoid stopping the pressure getting to the solenoid and only a vaccuum. then at the right revs the mpem switches the solenoid to let the vaccuum open or lift the valves

  9. #9
    PEST!'s Avatar
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    Quote Originally Posted by winterstick View Post
    no they would open at idle, they need to be activated at certain revs, the fitting on the case lets a pulsating action in the line, then there is a one way valve in the line going to the solenoid stopping the pressure getting to the solenoid and only a vaccuum. then at the right revs the mpem switches the solenoid to let the vaccuum open or lift the valves
    its around 5k RPM and its pressure not vacume from the Solenoid/crankcase/check valve.

  10. #10
    yeah pressure I went and checked mine, but they would still open at idle (or way too early) unless controlled by the mpem

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