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boost refrence

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    Senior Member vmaxed's Avatar
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    Default boost refrence

    I need for someone to explain to me real slow how the boost referenced power valves work. How does pressure out of the intake open a vacuum operated power valve? Also if you make say ten pounds of boost at six thousand how do you pick the right size power valve?
    Thanks
    Grady
    "DON'T JUST TELL ME IT WON'T WORK TELL ME WHAT WILL"

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by vmaxed View Post
    I need for someone to explain to me real slow how the boost referenced power valves work. How does pressure out of the intake open a vacuum operated power valve? Also if you make say ten pounds of boost at six thousand how do you pick the right size power valve?
    Thanks
    Grady
    Grady, if you are talking about a manifold referenced power valve for a roots blower setup , the source for the powervalve under the carb is plugged, redrilled and has external lines down to the manifold. Then manifold vacuum still holds them shut. This has to be done because a blower will draw hard enough on a carb to suck the powervalves closed and lean the engine out. The only other alternative is to jet up and plug the PV. You will need a vacuum guage to test the engine for the perfect powervalve.
    If you are talking about a blowthrough carb with a true boost referenced powervalve, these carb companies take a regular powervalve apart and put the spring on the opposite side of the plunger were it actually holding the powervalve closed, and then they use a boost signal to open them. I havent seen the version that CSU uses but I understand that its easily adjustable as to when and how much it opens. The C&S gets its signal through a hole in the carb stud and its reasonably easy to adjust as well.
    This vid gives a good view of a boost referenced PV


    Here is a link with a bunch of pics explaining the external referencing for a roots blower.
    How to boost reference your holley style carb - Third Generation F-Body Message Boards
    Last edited by Hass828; 01-15-2013 at 07:40 PM.
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    Senior Member vmaxed's Avatar
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    Default first time

    Doing my first blower set up and it's all a learning curve. Doing a 8:1 355 with a 671 and it has two 600 double pumpers that are boost referenced. It's going to be a hyd roller street ride so power valves will be a plus. Thanks.
    "DON'T JUST TELL ME IT WON'T WORK TELL ME WHAT WILL"

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by vmaxed View Post
    Doing my first blower set up and it's all a learning curve. Doing a 8:1 355 with a 671 and it has two 600 double pumpers that are boost referenced. It's going to be a hyd roller street ride so power valves will be a plus. Thanks.
    then you will be externally referencing them to the manifold. There's more than one way to do it but the most common is in the link I posted at the end of my last post.
    "if we keep doing it the same way we always do..we will always get the same results"
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    Senior Member vmaxed's Avatar
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    Default I see now

    I didn't understand how it worked. That explained it. It doesn't care what the pressure is, the P/V just opens when it sees a negative difference in inches of vacuum. I think I said that right.
    Thank
    Grady
    "DON'T JUST TELL ME IT WON'T WORK TELL ME WHAT WILL"

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    Quote Originally Posted by vmaxed View Post
    I didn't understand how it worked. That explained it. It doesn't care what the pressure is, the P/V just opens when it sees a negative difference in inches of vacuum. I think I said that right.
    Thank
    Grady
    Grady,

    If you want to see how this is plumbed, etc., you can take a look at Piazza's carbureted blower engine. One can work with the jetting and the power valve restriction size to obtain a real nice fuel curve. Clean cruise and proper fuel enrichment when your in the throttle.

    Gear

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    Senior Member vmaxed's Avatar
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    Default learning

    Gear I didn't even know the hose barbs from the metering blocks needed to be tied together and plumbed to the intake below the blower till I talked to Ryan Saturday night. But I still couldn't grasp how blowing ten psi into the metering block would allow the P/V to open. There aren't many offerings for a Hyd. roller SBC blower motor either. This will be a learning experience
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    gn7
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    Quote Originally Posted by vmaxed View Post
    I need for someone to explain to me real slow how the boost referenced power valves work. How does pressure out of the intake open a vacuum operated power valve? Also if you make say ten pounds of boost at six thousand how do you pick the right size power valve?
    Thanks
    Grady
    Grady, first you have to keep in mind that roots blown boost is not RPM sensitive. Its throttle position sensitive. You can hit max boost at 1000 rpm if the throttle is wide open. Engine speed means nothing. Load causes you to open the throttle, and opening the throttle will bring on the boost if its open enough.
    Like Hass posted, on a roots, the PV will never open. Its closed by vacuum, not opened by pressure. Its not boost that opens the valve, its the absence of vacuum that allows its own spring to push it open. Vacuum holds it shut against the spring.
    On a roots deal, from idle to flat out, the valve will always remain closed. Its not a matter of it closing and leaning out the motor like Hass posted(he knows better ), it only that it will never richen up.

    Now the IF, you need one.

    If you take any given engine and put it in a 30ft deep V, chances are you almost cannot drive the boat even at a slow cruise that it will have manifold vac. It will almost always have either very low vac, or be zero/neutral, or in slight boost. If you have a 4.5" PV installed, and the manifold is running at 3.0 at slow cruise, the valve is open.

    If you take the same motor and put it in a 18ft flat v drive, it might cruise with 5" of vac in the manifold. MIGHT!

    I have never been in a blower boat that the vac was sufficient to keep a PV closed during cruise, but I guess they do exist.

    You need to drive the boat like you normally do, read the MANIFOLD vac/pressure at your normal cruise speed and see what the vac/pressure is. If your have 5" of vac, then a 4.5 or 4" PV is what you need. If your really really need to have a PV, and your vac is 3.5, there are PVs that low, but I have never bothered with one that low.

    I think you will be surprised how little time your boat is in manifold vac.



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    Quote Originally Posted by vmaxed View Post
    Gear I didn't even know the hose barbs from the metering blocks needed to be tied together and plumbed to the intake below the blower till I talked to Ryan Saturday night. But I still couldn't grasp how blowing ten psi into the metering block would allow the P/V to open. There aren't many offerings for a Hyd. roller SBC blower motor either. This will be a learning experience
    WHOA. Do not confuse a hose barb sticking out of a metering block on a stock Holley as a external/manifold boost referenced PV. Its not!!
    On a stock Holley there MAY be a hose barb in the metering block, but that for timed spark advance on dizzys that use it.

    When they MODIFY a Holley for boost referenced PV, they just use the same spot on the metering block to put the hose barb, but its internally channeled to the PV. Its an entirely different deal

    IF you are talking about the port for a modified Holley with boost reference, then YES, you tee the two together and then to the manifold.



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    Senior Member vmaxed's Avatar
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    Default port

    GN these carbs have the vac ports threaded, tapped and plugged. The ports are slotted on the metering blocks to use the factory threaded port on the block.
    Thanks
    "DON'T JUST TELL ME IT WON'T WORK TELL ME WHAT WILL"

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    Quote Originally Posted by vmaxed View Post
    Doing my first blower set up and it's all a learning curve. Doing a 8:1 355 with a 671 and it has two 600 double pumpers that are boost referenced. It's going to be a hyd roller street ride so power valves will be a plus. Thanks.
    So this blown SBC is going in a street car ?
    If it is a power valve might be the ticket for you on a easy cruising run
    like Gn said get a vacuum gauge and see where your at
    If you ain't the lead dog the view is always the same !

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    gn7
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    Quote Originally Posted by vmaxed View Post
    GN these carbs have the vac ports threaded, tapped and plugged. The ports are slotted on the metering blocks to use the factory threaded port on the block.
    Thanks
    Thats great Grady, but that does not mean they are boost referenced, it means they have a timed spark port that was common as dirt on Holleys.

    It makes modifying them a "little" simpler, but they still need to be boost referenced if you are going to run PVs.
    There are 10 times as many threaded metering blocks out there as not. It means ZERO!

    I have modified a few Holleys for boost reference, and have no idea what "slotted ports on the metering block" even means. Never modified a metering block in my life for a referenced PV.



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    Last edited by gn7; 01-15-2013 at 10:08 PM.

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    Quote Originally Posted by BigSteve View Post
    So this blown SBC is going in a street car ?
    If it is a power valve might be the ticket for you on a easy cruising run
    like Gn said get a vacuum gauge and see where your at
    Agreed. If its a street car, a PV is the setup for sure. Light load cruise is easily accomplished in a car.



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    Senior Member vmaxed's Avatar
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    Default referenced

    GN I didn't explain that right, they were sent to a carb shop and referenced. But that's the way the set them up was to use that port on the side of the metering block. But my dumb ass thought it was all internal till I was told different. Then it blew my mind to blow boost back into the carburetor. The cam options are so limited in a Hyd roller for a SBC. I also thought they would have more lobe separation. We will learn maybe not on the first one but we will. It's just old kids playing huh?
    "DON'T JUST TELL ME IT WON'T WORK TELL ME WHAT WILL"

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