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  1. #1
    Water Bum Rodneyae's Avatar
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    BOV, Blow off valve.....

    Has anyone added a BOV to there ski?? I noticed in rough water letting off the throttle then when I hit it, it take a second to get the boost back up. So I am thinking about a installing a BOV. I just wanted to check and see if anyone else has done this.

    Rodney


  2. #2
    adding a BOV would make this problem worse. not only that but it would provide a point of entry for water if your engine got a good amount of water in the bay or flipped.

    adding a BOV relieves boost pressure from your system, which in turn the turbo/supercharger has to work to replace that pressure back, what you want is a recirculating valve, it has an entry and exit port, the exit gets ported back to the intake system pre-turbo. that recirculates that pressure back into your turbo allowing for your psi to maintain a more constant level of pressure as long as possible.

    check out the engines from the cars of the WRC rally, they all use this method of recycling the excess pressure back into thier engine. most stock turbo cars use this as well,the GTI, the Volvo, Audi, etc..

    BOV would sound pretty awesome on a PWC, but for performance wise, it wont help, and in some case will make turbo lag worse

  3. #3
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    i been using one on my Honda for about 3 years now. I use it to protect the Over-sized large turbo i have. It keeps the turbo from being dead headed and ruining the compressor blades at 23-24 psi.

    I know Superjim has one on his stocker for about 5 years now no problem.

    shawn

  4. #4
    Water Bum Rodneyae's Avatar
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    Quote Originally Posted by daewootech View Post
    adding a BOV would make this problem worse. not only that but it would provide a point of entry for water if your engine got a good amount of water in the bay or flipped.

    adding a BOV relieves boost pressure from your system, which in turn the turbo/supercharger has to work to replace that pressure back, what you want is a recirculating valve, it has an entry and exit port, the exit gets ported back to the intake system pre-turbo. that recirculates that pressure back into your turbo allowing for your psi to maintain a more constant level of pressure as long as possible.

    check out the engines from the cars of the WRC rally, they all use this method of recycling the excess pressure back into thier engine. most stock turbo cars use this as well,the GTI, the Volvo, Audi, etc..

    BOV would sound pretty awesome on a PWC, but for performance wise, it wont help, and in some case will make turbo lag worse


    You a part right but compleatly wrong about BOV.... Not getting into this. I used to build I boost car for a living, I currently have a vintage nissan Z car boosting 30 PSI and putting 500 HP to the rear wheels. So when it comes to charged systems I know what I am doing, I just wanted to know if anyone has done it to these small displacment engines and if there is any noticable advantage. I do not care about sound I am all about funtional/performance. But Thanks

  5. #5
    Water Bum Rodneyae's Avatar
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    Aslo thinking about using a water/methnal injetion system to lower intake temps more.

  6. #6
    Water Bum Rodneyae's Avatar
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    Quote Originally Posted by NitroShark View Post
    i been using one on my Honda for about 3 years now. I use it to protect the Over-sized large turbo i have. It keeps the turbo from being dead headed and ruining the compressor blades at 23-24 psi.

    I know Superjim has one on his stocker for about 5 years now no problem.

    shawn
    Thanks, But do you notice a differance when letting off the throttle for a second and getting back on it? I have a couple of left over 1st gen mitsu BOV's with flanges laying around. I am thinking about moding one of them to fit. If you crush them in a vise they will hold 32 PSI of boost before they start leaking.

  7. #7
    Water Bum Rodneyae's Avatar
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    Here is a pic of a Mitsu, 1st gen BOV or Recurtion valve looks like. The only advantage of plumbing it back into the system is if you have a mass aif flow meter, it keeps the A/F ratio from dipping rich for a couple of m/s. And there is no noise. A filter can be fitted to one that will keep out water if that is an issue for you. As they are closed until you let off the throtte, to relive pressure. A small amount of water in a charged engine will cool the charged air slightly, giving a slightly cooler, denser air charge, it will also keep down the carbon build up, as you are "steam cleaning" the inside of the engine. But with the water injection you have to keep it too a small amount. I might get the welder and grinder out and install one.



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  8. #8
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    i only have a BOV on my highly modified F13x so i cant really say i see much difference in accell and decell. it just takes off

    4 years ago i started a intercooler project and a year later release one that is about 3x larger and drops the intake charge from 245F to about 95-105F. it really made a difference.

    i got a recording if you need to see it. just start a new tread about those kind of mods.

    sg

  9. #9

    How BOVs Affect Performance

    Hi, as you've been playing with the Nissan Z, you've obviously got a handle on the setup of these things. When i found out that they don't run a BOV as standard i was shocked to say the least.

    The reason you use a BOV is to allow the turbo to keep spinning when you close the throttle. By not using a BOV, the air that was being forced into the engine with the throttle open suddenly has no where to go when the throttle is closed. This creates a pressure wave that travels back down the inlet into the turbo, now this causes several detrimental effects.

    1. it can stop the turbo impeller from spinning which means there will be a significant lag when you get off then on the throttle because the exhaust gasses then have to bring the turbine back up to speed. By using a BOV you vent only the excess pressure in the intake allowing the turbo to keep spinning at speed so that when the throttle opens again the turbo can get straight back to making boost.

    2. It can create massive amounts of wear to the turbo impeller and turbo's bearing. With the shock wave that travels from the throttle back to the turbo impellor, it would put quite a bit of pressure on the impellor shaft bearing. This can lead to the turbo failing via a water leak around the shaft into the intake. (I've seen this happen to a guy who had a really crap setup on a Nissan 240sx, running Way to much boost for the stock BOV, 28 PSI, Stock is 7 PSI) I'm in the process of buying a F12X so i haven't had a chance to have a good look at how honda gets round these issues. The only thing i can think of is that they've created a dampening system in the intake to reduce the effect of the surge.

    As to which one to use, the plumb back versions of the BOV with the outlet feeding back into the airbox i feel would be the way to go, as it removes the possibility of water getting into the intake.

    Having said all this i'm coming from a back ground in small capacity turbo charged cars like yourself so whether the amount of air being shifted by these smaller displacement engines is significant enough to cause this is the real question. I can see it assisting, performance wise, where there is need for getting on and off the throttle quickly also in the longevity of the engine/turbo combo. But a BOV is never going to increase power output.

    O yeah, BOV's will not increase lag at all, quite the opposite in fact.
    I may be missing something being marine engines but the aerodynamic theory should trasfer without change.

  10. #10
    Running a BOV from my experience is fine. You would be hard pressed to ever get enough water into the engine compartment for that to be a concern. Also BOV's are closed unless they are releasing boost. So there is almost ZERO way to get water into the motor through a good one. HKS, etc.

    I ran one on one of my R-12X's for about 2 years. Noticed zero difference in spool, but enjoyed the sound. However the stock engine compartment is sealed up so tight it's pretty darn quiet.

    Down side is that occasionally when jumping big waves and releasing the throttle quickly it would confuse the map sensor and die. Pretty annoying.

    Otherwise all good.

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