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Thread: B.O.V.'s

  1. #1
    Moderator two2curupt's Avatar
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    B.O.V.'s

    Still trying to figure out the benifit of having one??? I think they are just for show..First off the supercharger system on our machines runs directly off a gear attached to the motor...So as rpms decrease so too does boost..and if it did relive pressure would that not be the same as spooling the system...Alot like what was causing the clutch failure in the first place??? I have heard of none of the rotax racing machines using these in Europe so I just don't see an advantage to them..
    If someone could let me in on the secret to who and why someone came up with this system I would be interested to know...Sounds like it was someone in the turbo industry..
    Just Curious..


  2. #2
    Site Admin Green Hulk's Avatar
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    Mike, very good point! Mark Underwood doesn't recommend them either.
    I guess they just add to the "cool" factor!

    My feeling is if you install the Rotax Racing heavy duty clutch you shouldn't have to worry about it for a long long time.

  3. #3
    Site Admin MikeTrin's Avatar
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    Here's my take on it.

    edited... These aren't blow off valves or waste gates, it's my understanding they are bypass valves.

    Clutch failure is caused by friction modifiers in oil and synthetic oil. These modifiers coat the cluch, making it constantly slip. I mean that's the job of friction modifiers, reduce friction! It's good for every part of the engine but a wet clutch. Maybe I am wrong but I have heard of no 04 or 05 clutch failures. In the 03 supercharger they used a lesser quality material for the clutch AND synthetic oil with friction modifiers. Mine was one of the first to go that I know of, the fix was mineral oil 10w-40 and a ceramic clutch.

    I could be wrong, maybe they are still failing. I do know that riding in rough water at high speed where the impeller comes unhooked and you hit the revlimiter, then you hook up and load the engine over and over and over is hard on the clutch.

  4. #4
    Sunfunzoom's Avatar
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    Another advantage of the BOV, is when your at idle, the SC actually pumps more air than the engine wants, so it builds up pressure prior to the throttle body. The BOV vents this pressure at idle and at any rpm where the SC is producing more than the engine can take. (mostly below 4500 rpm).
    So when your idling,around, your actually loading then engine a little for no reason.
    Basically the bov keeps the loads on the SC Clutch more even with less abrupt pressure changes.
    It also helps acceleration, I dissabled the BOV and the ski felt a bit slower (top speed was the same) and not as eager to wind up.
    Just a note on what a BOV does, it does not vent at a certian PSI, thats a waste gate. A BOV maintains the same pressure on both sides of the throttle plate reducing pressure waves when the throttle is opened and closed.

  5. #5
    CRAZEDRXP's Avatar
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    It's not a blow-off valve, it's a by-pass valve. It opens when there is vaccum in the air box. Like when the throttle is either closed or not allowing enough boost into the air box to trigger closing of the by-pass valve.

    It saves the supercharger clutch by allowing the excess air pressure between the supercharger and a closed throttle body to escape instead of causing the supercharger impeller to slow down faster than the engine rpm, which causes the clutch to slip.

    A blow-off or pop-off valve is used mainly on turbocharged engines to release excess pressure as a turbocharger is not mechanically tied to engine rpm, like a supercharger, and will continue to produce very high boost levels after getting off the gas as there is really nothing to slow it down quickly. A pop-off or blow-off valve releases based upon excess pressure in between the turbocharger and the throttle body, not vaccum in the air box like a by-pass valve.

    That's why you feel air coming out of the filter when the motor is at idle and when you give it a little gas. Give it a lot of gas and you will feel the air coming out of the by- pass suddenly stop

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    CRAZEDRXP's Avatar
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    I will say this now ... just because RR doesnt use them doesnt mean its a waste .. Glenn Told me directly that installing a s/c imp. would do nothing at all and it is a total waste and he doesnt run them on his boats ... The s/c imp. is BY FAR the best Single mod I ever done to my ski ... Mark from RR prob doesnt use or sell them because the simple fact he wants you to buy his Bullet proff clutch set up ... Sometimes you cant go with just one person says .. I been racing mustangs for many many years .. All blower cars .. Vortech s/c s trims t rims with mondo coolers I know a LITTLE bit about s/c motors .. That boost needs somewhere to go when u come off of boost esc. at full thortlle !!!! Just put one and put your hand near it when its idiling and You will feel the air flying out of the filter elelment!!! where was that air going before???? Thats what the clutches where for ... IT is a MUST if you do not have the RR clutches

  7. #7
    Phil's Avatar
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    Re: B.O.V.'s

    Quote Originally Posted by two2curupt
    Still trying to ..
    Just Curious..
    Mike,

    You are alive! Glad to have you on this forum. I am curious as to the props you have tried?

    I am trying a 15/20 Impros this weekend. I will post my results.

  8. #8
    rx4pain's Avatar
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    I got a BOV for someone with a Stage IV to try...
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    rx4pain's Avatar
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    This is a TurboXS high performance BOV. I had it on my Stage III WRX. Sold the car and forgot to put the BOV back on (winter). I also have a new and unused underdrive pulley kit for the WRX. And also like 5 new 3rd generation RX7 oil filters...anyone want to help me clean out my garage?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  10. #10
    Moderator two2curupt's Avatar
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    hey Phil good to hear from you agian...I am still using the stock prop..But I might try something a bit different this year..You been out this year yet?? If so how many kills do you have so far..

    Hey guys not nessisarily knocking the B.O.V.'s waste gates or by pass valves...Just curious about them that's all.. Rotax does kind of know what is going on too..And I mean the developers in Europe mostly..I was just wondering if anyone had any proven test results or are we all just doing things on theory here..If that's the case than why don't we just ask all the mustang mechanics to set up our ski's..Maybee we will get them into the low 10's on the drag strip..Or better yet lets ask bombardier why they don't put Ford motors in thier ski's?? Everyone and thier brother seems to know how to modify them properly...Or even further lets call Ford and ask them why they don't put a fourstroke supercharged motor in thier Mustangs??
    Just teasing crazedrxp...I have a very sarcastic sense of humor..
    I see your point on the B.O.V.'s as well. I guess what I am saying is that it might make sense but DOES IT WORK??

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